Ch Col Education

JOURnflL OF MARCH 1984 Ch col Education

Published by the DIVISION OF CHEMICAL EDUCATION OF THE AMERICAN CHEMICAL SOCIETY Before you order chemicals again,

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Matheson belongs in the modern laboratory. fcgflatheson ••Gas Products World Leade30 Seavier rwn SpecialtDrive, Secaucusy Oase, sK JS .0709 Equipmen4 t Circle No. 18 an Readers' Inquiry Card Volume 61 Number 3 March 1984 A71 YOUR ACCESS TO EXCELLENCE BEGINS HERE.

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U.S, Domestic prices only. HEWLETT PACKARD Circle Reader Service Number 34 for more information J. J, LAGOWSKi, Editor University of Texas at Austin March 1984 Volume 61, Number 3 Austin, Texas 78712

Assistant Editor: JOURflffL Of Oebora Ann Blttaker

Editorial Assistants Linda Davis Kyle George V. Oilver Chemical Education Rebecca Chambers Marie S. Stephens Owned and Published by the DIVISION OF CHEMICAL EDUCATION OF THE AMERICAN COMICAL SOCIETY

JAMES V. DEROSE Publications Coordinator Articles in this Issue ADVERTISING MANAGEMENT CENTCQM, LTD. P.O. Box 231 25 Sylvan Road South The G. N. Lewis Symposium Weatport, Connecticut 06881 (203)226-7131 185 Reflections on the Electron Theory of the Chemical Bond: 1900-1925 (For list ol offices, see page A78) Anthony N. Stranges NEW PRODUCTS 191 Abegg, Lewis, Langmuir, and the Octet Rule William B. Jensen Shirley SJeratzki 201 G. N. Lewis and the Chemical Bond Linus Pauling Journal of Chemical Education Centcom, Ltd. 204 The Triplet State: An Example of G. N. Lewis' Research Style 60 East 42nd St. Michael Kasha New York, N.Y. 10165 (212) 972-9660

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SECONDARY SCHOOL EDITOR 217 Photoelectrochemical Solar Cells John T. McDevitt Mickey Sarquis 221 Thermodynamic Inefficiency of Conversion of Solar Energy to Work Miami Unlversity-MidcHetown Mlddletovm, OH 45042 Arthur W, Adamson, James Namnath, V. J. Shastry, and Vida Slawsort 22S The Evaluation of Empirical Resonance Energies as Reaction ASSOCIATIONS EDITORS Vasu Dev Enthalpies wlih Particular Reference to Benzene California Association of Chemistry Teachers Philip George, Charles W. Bock, and Mendel Trachtman Percy Ehrllch 246 The Basic Elements of Writing a Scientific Paper: The Art of Scientific New England Association of Chemistry Teachers Style Carol Potera 248 Scenarios In Science Sharon J. Sherman and Alan Sherman BOARD OF PUBLICATION Division of Chemical Education D. W. Brooks W. B. Cook D. A. Davenport Features I. D. Eubanks M. H. Gardner D.Kotb 183 Editorially Speaking J. W. Moore W. J. Stratton 230 Report of the Polymer Core Course Committee: Inclusion of Polymer Topics in Undergraduate Inorganic Chemistry Courses The Cover 237 Textbook Forum: Who is Anti-Markovnikov? J. M. Tedder The spectral distribution of energy from tfie 251 Tested Demonstrations edited by George L. Gilbert son is used on this month's cover to draw 267 Letters our readers' attention to several articles in A83 Safety in the Chemical Laboratory edited by Malcolm A. Renfrew this issue which discuss the problems of Experiments Integrating Evaluation of Chemical Hazards into the converting this energy to useful work. Chemistry Curriculum J. T. Pierce, S. M. McDonald, and M. S. Scogin A89 Topics in Chemical Instrumentation edited by Frank A. Settle, Jr. col education Choosing the Right Instrument: The Modular Approach; Part fl Howard A. Strobei A113 Book Reviews

Secondary School Chemistry

216 A Simple Aid for Teaching the Theory of Aiomic Structure Hung-cheh Chiang and Chirtg-Hwei Tseng 228 A Place for Chemists: Analytical Chemistry Michael D. Seymour 236 Discovering Watson's Crick in High School Chemistry Mark Whitman )LAR 239 Goals Why Teach Organic Chemistry Leallyn S. Ciapp ERGY The Place of Organic Chemistry in the High School Curriculum Mary C. Johnson (Continued on page A74)

Volume 61 Number 3 March 1984 A73 241 Profiles in Chemistry: Neoprene and Nylon Stockings: The Legacy of Wallace Hume Carothers Carol Cummings Capture a 242 The Density of Solids Dale Burgess 243 Use of the Computer for Chemistry Instruction Robert Suder Teacher 249 Thumbnail Sketches: Is Sugar from Sugar Beets the Same as Sugar from Sugar Cane? W. Conard Fernelius and you 250 Safety Tips: Peroxides Can be Treacherous Miriam C. Nagel 255 Filtrates and Residues: Spectrophotometry: Mechanics and Measurement Susan M, Dieht-Jones capture a 266 What's Happening in Your Part of the Country?

Generation The haif-billion dollar academic market for scientific products is composed of professors who 252 Chemical Storage of Solar Energy Usfng an Old Color Change teach, who buy in volume, and who Demonstration L. Gene Spears, Jr. and Larry G. Spears read... 257 A New Method of Separating 210Pb from Ra-DEF for a Radioactive Equilibrium Experiment C. M. Wai and J. M. Lo 259 Growth and Decay: An Experiment Demonstrating Radioactivity Relationships and Chelate Solvent Extraction Separations D. M. Downey, D. D. Farnsworth, and P. G. Lee 262 Phosphorus Determination by Derivative Activation Analysis; A Multlfaceied Radiocnemical Application E. W. Kleppinger, E. H. Brubaker, R. C. Young W. D. Ehmann, and S. W. Yates 264 HPtC Analysis of Chlorophyll a, Chlorophyll b, and ^-Carotene in Coilard Greens: A Project for a Problem-Orlenled Laboratory Course Augustine Silveira, Jr., Jerry A. Koehler, Edward F. Beadei, Jr., and Pearle A. Monroe

190 The Amazing Periodic Table James E. Fintiolt 258 A Simple Method for Cleaning Mercury Benjamin Jenkins and Ian D. Jenkins Sell Today/ 261 Double Balloons—Long Term Protection for Sensitive Materials Robert C. Duty Insure Tomorrow In addition to constituting a huge market themselves, the professors who read the Journal of Chemical Education help to mold the brand preferences of succeed- tyr Experiments, iabofalory exercises, lecture demonstrations and other descriptions ol the use ol chemicals, appa- ing generations of scientists. ralus and instruments are presented In THtS JOURNAL as initiative 0' new. novel of (rnproveo" Idaos or concepts in chernlsliy instruction, ancs are directed a! quanted teaenws, Altlicsign every effort is made 10 assure and encowiage sale practices and sale In a major study recently con- use at chemicals, the JOURNAL OFCHEMICAl EOUCATtoncannot assume lesponsiblity lor uses made ot its published materi- ducted for the Scientific Appa- ala. We strongly urge afi those planning 10 use materials from our pages to make cho«*s and to develop procedures tor Isburatc- ratus Makers Association by • ry end classroom saiely In accordance will? local needs and sitwitiore. Copeiand Economics Group, Inc., they state".., CEG has found that the equipment and apparatus a scientist uses in the training process tend to be the types and brand names that he seeks when Manuscripts 'or publication. Docks lor review, and correspondence regarding papers, proofs, and orders forreprlnte should t>g sent 10 the he assumes a research position in office of the Editor: J. J. LagoWBki, Journal ot Chemical education. Deptr 01 Chemistry, Univgrstty of Texas, Austin. Ten. 7B712. Manuscripts Tor trie Secondary-Softool Section can be serrt directly to: Ms. Mlcfcey Sarquls. High School Editor, Journal of Chemical Education, Miami, industry or government." Urmers%.Mat»etQ™, 4200 East Unfters%BM..M^^ 1981* page SQ36 for corracl format and 6tyte guidelines. Subscription pries tot Individuate: U.S.A. $20.00 par year, all other countries $35.00 per year. Subscription price lor Call 215-667-9666 libraries, instllutleng ami companies: U.S.A. $40.00 par year; all other countries $45.00 per year. Single conies $6.00 US, $6.40 Foreign. Volume |12 copies lor a calendar year) $55.00. Single copies ol Issues available lor the preceding ... and get the full story on 15 years only. Orders for subscriptions, single copies, remittances and changes ol address should be sent lo Journal ot the huge academic marketplace Chemical EAicationi Subscription and Book OroW Department. 2«h and Northampton Sts.. Easton, Pa. 180*2. Subscribers requesting an address change must give 6 weeks notice, submit label with oM address, and submit new address with zip for scientific products. Ask for code. Foreign remittances must be made by international money order, bank draft payable at a U.S. bat*, or UNESCO Jim Byrne, Advertising Sales coupons. Manager, Chemical Education. rJoclfllEnsforcOBtafiaf jDtffnals lost IrrtnamflHscanbeBUowedifl'lBss&uchclaJEnsarB received within sflcty (60) daya of The date ol lasue; no claims can bs alkiwed tor Issues lost BS a raautt of inBuRlciont nollca of change ol address. SecomWlass postage paid at MoOB, Pa. and addJtianaF mailing otflce. Three cumulatrye indexes are available: W-¥ear CumulallW! Mm, Volumes t to 25:10-Yew Cumulali™ fcidw, Volumes JOURTIALOF 36-35; tO-Yeai Cumulative Index, Volumes 36-45, The selling price ot each cwnulatlYe Index, including postage and handling costs, is S9.50 US and $9.90 foreign. Prepaid orders should be addressed to Subscription and Book Order De- partment Journal ot Chemical Education. 20tft and Northampton Streets, Easton, PA 18042. Chemical Education ©Copyright 19S4 oy Division of Chemical Education. American Chsrnlcal Sectary . Advertising Management: Centcom, Ltd. A74 Journal of Chemical Education How much computing power

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You can get enough to linear systems of equations. Sparse, locations throughout the world and diagonalize a 100x100 disk-resident matrices with up to take advantage of remote diagnostic several billion non-zero entries can be capabilities, comprehensive docu- Hamiltonian in 1.8 seconds. factored at speeds of over 10-million mentation and software support. You can aiso compute a million spin floating-point operations per second. updates in a second on a 3-D Ising A 2,000 x 2,000 symmetric matrix can To learn more. model or solve a tridiagonal system of be factored in iess than 11 seconds. 300,000 equations in one second. A math library with more than 400 Call us, or write to find out how The FPS-164 Scientific Computer highly-optimized subroutines for basic cost-effective scientific computing is from Floating Point Systems gives you and advanced mathematical opera- on an FPS-164. Our toll free number that kind of computing power for a tions is also available. is(800) 547-1445. fraction of the cost of a large main- frame or supercomputer, Its 64-bit, parallel, pipelined architecture, 58 Proven Reliability and FLOATING POINT megabytes of memory and speeds of Support. SYSTEMS, INC. up to 12-mi!lion floating-point opera- Floating Point Systems has estab- tions per second gives you the lished an impressive record for prod- capability needed for solving very uct reliabiiity and service. Customers P.O. Box 23489 large problems. Portland, OR 97223 can use service facilities located at key (5031641-3151 TLX: 360470 FLOATPOiN BEAV

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COLLEGE MARKETING • 866 THIRD AVENUE • NEW YORK, N.Y. 10022 Circte No. 17 on Readers' Inquir Advertising in this issue ON COUPONS IN ADS The companies listed below Readers who do not want to damage evidence their interest In chemical education by their presence as advertisers. their issue by cutting out coupons found This advertising brings to oir subscribers information about new books, new in some advertisements are requested and established laboratory equipment, and apparatus and instruments for to make a photo copy of the coupon for both teaching and research. Get acquainted with the advertisers in your use in inquiring about items mentioned In the ad. Journal. Do not hesiitate to write for their catalogs and literature. Use the Readers' Inquiry Cards found on the white insert at the back of this issue. When contacting advertisers by letter or phone, be sure to mention the Journal of Chemical Education.

INDEX TO ADVERTISERS HI THIS ISSUE

CIRCLE CIRCLE INQUIRY NO. ADVERTISERS PAGE NO. INQUIRY NO, ADVERTISERS PAGE NO.

1 Academic Press A100 xx Shapely Molecules A114 . 2 Addison-Wesley Publishing Company ASS xx Spectrex Corporation A114 A-W Advertising Associates 29 Springer-Verlag A84 xx American Chemical Society A111, A112 xx Thorn Smith, Incorporated A114 3 Brtnfcmann Instruments OBC 25-28, 28 John Wliey 8 Sons. Ino A80-A81, AB8, A97 Lavey/Wolft/Swift, Inc. 605 Advertising Group 4 Burgess Publishing Company A90 Burgess-Beckwith 5 Carolina Biological Supply Company IFC Advertising Management for the Journal of Chemical Education « Cross Educational Software A114 CENTCOM, LTD. 35 Floating Point Systems, (no A7S Thomas N. J. Koerwer, Presfdent 7 GHian Instrument Corp A92 James A. Byrne, Vice President S. M. Sachs & Associates, inc. Alfred L. Gregory, Vice President Clay S. HWden, Vice President 34 Hewlett-Packard Company A72 Benjamin W. Jones, Vice President Pirtne, Garvin, Harbors & Hock, Inc. Robert L. Voepel, Vice President Joseph P. Stenza, Production Director xx Houghton Mifllirt Company ASB-A99 Houghton Advertising 25 Sylvan Road South 9 institute for Scientific Information A91 P.O.Box 231 Greene Towne Associates, Inc. Westport, Connecticut 06681 (Area Code 203)226-7131 10 instrument for Research a Industry A85, A114 Telex No. 643310 Kenyon Hoag Associates ADVERTISING SALES MANAGER xx JSS Software A114 James A. Byrne 33 Kontes Scientific A92 ADVERTISING PRODUCTION MANAGER Lab-AO Associates Joseph P. Stenza 14 Laboratory Craftsmen, Inc A10O SALES REPRESENTATIVES 15 Laboratory Devices A100 NEW YORK: John F. Raftery, Centcom. Ltd., 60 East 42nd St., New York, H.Y. Robert W. Lesleur & Associates 10165. Telephone: 212-972-9660. 16 Lab Safety Supply Co A84 PENNSYLVANIA: John F. Raftery, Centcom, Ltd. GS8 8ldg., Suite 425.1 Bet- janesville Ad Agency mont Ave., Bala Cynwyd, PA. 19004. Telephone: 215-667-9666. CONNECTICUT: John f. Raftery, Centcom, Ltd., 25 Sylvan Road South, P.O. 17 MacMlHan Publishers A76-A77 Box 231, Westport, CT 06881. Telephone: 203-226-7131. Telex No. Ftamm Advertising, Inc. 643310. OHIO: John F. Raftery, Centcom, Ltd., 325 Front Street, Suite 2, Berea, OH. IB Matheson A71 44017. Telephone: 216-234-1333. Kenyon Hoag Associates ILLINOIS: John F. Raftery, Michael J. Pak, Centcom, Ltd., 540 Frontage Rd., NorthtieW, IL. 60093. Tetephone: 312-441-8383. 30 Mettter Instrument Corporation A82 SAN FRANCISCO: Pay! M. Butts, Centcom, Ltd., Suite 112, 1499 Bayshore McKinney, Inc. Highway, Burlingame, CA 94010. Telephone: 415-692-1218. LOS ANGELES: Ctay S. Holden, Centcom, Ltd., Newton Pacific Cenler. 3142 IB Ohaus Scale Corporation tBC Pacific Coast Highway, Suite 200, Torrance. CA. 90505. Telephone; Jarman, Spitzes s Felix 213-325-1903. UNITED KINGDOM: Reacting, England—Malcolm Thiele, Techonmedia, Ltd., xx Programs for Learning, inc A114 Wood Cottage, Shurlock Row, Reading RG10 0Q£, Berkshire, England. 20 Sargent-Welch Scientific Co A7S Telephone: 0734-343302. Lancashire, England—Technomedla, Ltd., c/o Meconomics Lid., Potytech Advertising Meconomics House, 31 OKI Street, Ashton Under Lyne, Lancashire, 31 Saunters College Publishing A86-A87 England. Telephone: 061-308-3025. Doyle Dane Bernbach, Inc. CONTINENTAL EUROPE: tntemationaS Communications Inc., Rus Mallar 1,4800 Vervlers, Belgium. Telephone: (087) 22-53-85, Telex No. 49263. 21 Sensorex A84 ASIA: Shuji Tanaka, International Media Representatives Ltd., 2-29 Toranomor 10346 Agency 1-Chrome Minato-ku, Tokyo 105. Japan. Telephone: 602-0656.

A78 Journal of Chemical Education A way to bore a smooth, uniform, straight, properly sized hole in a rubber stopper —quickly, easily, safely and with any desired orientation.

Required are (1) a Anyone who has bored effortlessly— and even novei cutter grooved to a rubber stopper by hand off-center or at an angle, bring fresh lubricant to knows that it is a case of as desired. the cutting edge and trading hard work for A iarge selection of other areas of the cutter: poor results. At best, the interchangeable cutters stopper interface con- hoje is ragged, non- provides the exact bore tinuously during the uniform and frequently size for every application boring operation and (2) crooked. and corks and rubber a modified dril! press Custom boring need stoppers of any size can which drives the cutter not be so frustrating an be accommodated. Hoie and sets its orientation to experience. With our sizes start at 3 mm and the stopper. Power Boring Machine range to 22 and 32 mm stoppers (and corks) are for stoppers and corks, bored perfectly —with a w.™ij(v,.3rcut bore respectively. straight, smooth, uniform , cormgsts with ofte bored bore—quickly, safely and mandaFly

Put these two together The Power Boring and you have our Power Machine includes six Boring Machine —a real commonly used cutters, skin and temper saver three holders for small which belongs in any stoppers, a bottle of laboratory doing even a lubricant, an ejecting rod, moderate volume of cus- a cutter sharpener and a tom boring of stoppers. 3-wire cord and plug.

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Treats potentkjmetric, galyano- expanded thermodynamic data. ground is covered for each technique, and at static, potentiostatic experiments and includes least one example of its application—taken material on electrode double layer techniques, 780 pp. 1981 from the research literature-—is described rates of processes, first-order reactions, cata- (1-04831-3) $64.95 Cioth in detail. lytic processes, dimerization complexes, polar- (1-09173-1) $37.50 Paper approx. 325 pp. March 1984 ography adsorption, cyclic methods, kinetic (1-89369-2) $34.95 processes, and depolarizer transport. 255 pp. 1983 (1-09028-X) $45.00 INTRODUCTION TO POLYMER OPEN TUBULAR COLUMN VISCOELASTICITY, 2nd Ed. John J. Aklonis & William J. MacKnight GAS CHROMATOGRAPHY FIESER AND FIESER'S Theory and Practice A molecular approach to the fundamentals REAGENTS FOR ORGANIC of viscoelastic behavior in polymers, bridging Milton L Lee, Frank J. Vang & SYNTHESIS, Vol. 11 the gap between introductory accounts and Keith D. Battle Edited by Mary Fieser advanced research-level monographs. This A state-of-the-art treatment of one of the most Covers reagent literature published between updated edition includes new coverage of the wideiy applied methods in analytical chemis- July 1981 and December 1982, citing new theory of reptation, the kinetic theory of rubber try. Provides an integrated, in-depth view of reagents introduced during this period as well ejasticity, and an entirely new chapter on modern practice, summarizes the theory as recent references to reagents included in dielectric relaxation. Presents all derivations underlying this powerful technique, and ana- in detail, and treats concepts and models, previous volumes. The focus is on those paying special attention to assumptions, lyzes the relationship between theory and reagents leading to important new synthetic simplifications, and limitations. applications. pathways. 445 pp. February 1984 295 pp. 1983 (1-88024-8) $48.00 approx. 864 pp. June 1984 (1-88628-9) in Press (1-86729-2) $39.95

ADVANCED INORGANIC! GUIDE TO THE CHEMICAL CHEMISTRY: A Comprehensive PHYSICAL CHEMISTRY OF INDUSTRY Text, 4th Ed. SURFACES, 4th Ed. Products, R + D, Marketing R Albert Cotton & Geoffrey Wilkinson and Employment Arthur W. Adamson Chemistry and Industry called the previous Revised and completely updated editbn of the William S. Emerson editions,". ..the best available..." and with its classic text in the field for more than 20 years. A comprehensive review of f he total industrial thorough revision this fourth edition will prove Covers surface chemistry from the physical chemical picture, helping students prepare for equally valuable. chemist's point of view, dealing with basic the- the transition from the academic to the indus- This latest version of this highly popular ories and models, with many illustrations from trial world. Contains scientific, managerial, manual retains the same comprehensive yet current literature. Features about 20% new and economic material, examining the inter- balanced treatment of inorganic chemistry material, including updated chapters on mono- play of all these components in the operation while bringing you developments since 1966 of molecular films and on high-vacuum or "dry" of the chemical industry. physical methods and concepts. surface chemistry. 352 pp. 1983 1,396pp. 1980 664 pp. 1982 (1-89040-5) S35.00 (1-02775-8) $37.50 (1-07877-8) $42.95

A80 Journal of Chemical Education Wiley-Interscience Chemistry Texts for Spring 1984

TEXTBOOK OF POLYMER REACTIVE MOLECULES THE INTERPRETATION OF SCIENCE, 3rd Ed. The Neutral Reactive ANALYTICAL CHEMICAL Fred W. Billmeyer, Jr. Intermediates in Organic DATA BY THE USE OF An updated revision of the classic, besl-selting Chemistry CLUSTER ANALYSIS polynw science textbook. Surveys theory and Curt Wtentrup D. Luc Massart & Leonard Kaufman practice in a!! major phases o! polymer set- erics, engineering, and technology, including A unique, pedagoqicaily sound text and mono- A user-oriented introduction to clustering polymerization, solution theory, fractionaiion graph describing tne formation, detection, and methods, including both hierarchical and non- and molecular-weight measurement, solid- chemistry of neutral reactive intermediates hierarchical methods. The text shows how slate properties, structure-property relation- (free radicals, dtradtcals, carbenes, nitrenes, clustering can be used to interpret targe quan- ships, and the preparation, fabrication and slrained rings, and anttaromatics). Starting tities of analytical data, and discusses the rela- properties of commercially important plastics, from first principles, it brings the reader up-to- tion of clustering to other pattern recognition fibers, and elastomers, date on the current state of research en these techniques. approx. 550 pp. March 1984 intermediates. 237 pp. 1983 (1-03196-8) $34.95 325 pp. March 1984 (1-87639-9) $34.95 11-07861-1) $49.00

INTRODUCTION TO SAFETY HANDBOOK OF AIR ENGINEERING HEAD SPACE ANALYSIS AND POLLUTION TECHNOLOGY David S. Gloss & Miriam Gayte Wardie RELATED METHODS IN GAS Edited by Seymour Calvert & An overview of safety engineering, examining CHROMATOGRAPHY the broad range of areas and problems thai av. loffe & A.G. VHenberg Harold M. Ertglund confront engineers and other health and Treats the new and rapidly developing inde- A practical, uj>to-da!e handbook presenting safety professionals. Discusses accident pendent field in gas chromatographic analysis essential principles, design methods, exam- conditions and control, toss control, human based on the use of "out of column" phase pies, useful data, and reference information on resource development, management and equilibria and partition coefficients in gas-liq- air pollution and its control. Comprehensive in training, design assurance, health care, and uid systems. Describes new methods of head scope, it offers the best available source of occupational design, space anaiysis for the first time, plus related guidance for the design of cost-effective air approx. 532 pp. February 1984 pollution control systems, (1-87667-4) $50.00 methods based on the equilibrium between liquid and gas states. Describes prtystco- approx. 1,200 pp. March 1984 cKemicai applications of this new method, (1-08263-5) $74,95 DESIGN AND APPLICATION approx. 212 pp. February 1984 OF PROCESS ANALYZER (1-06507-2) $60.00 INTRODUCTION TO SYSTEMS PHOTOELECTRON Paul E. Mix A PICTORIAL APPROACH TO SPECTROSCOPY A comprehensive compilation in handbook MOLECULAR STRUCTURE style of in-line analyzer systems. This "hands- AND REACTIVITY Pradip K. Ghosh on" approach is the first to combine these ana- Robert F. Hout, Jr., Warren J. Hehre & A comprehensive, highly lucid survey of photo- lyzers and their respective sample systems in electron speciroscopy. Discusses applications one text. Treats sample system design, types William J. Ptetro that include the direct determination of atomic of continuous in-line analyzers and their A presentation of the valence molecular orbit and molecular energy levels and structures, theory of operation, and design features and ais of organic, inorganic, and organometailic and the study of solids and surfaces. applications. compounds, illustrating how they may be used to approach problems of chemical structure, 377 pp. 1983 approx. 250 pp. May 1984 stability, and reactivity. Broad in scope, the (1-06427-0) $55.00 (1-86518-4) $45.00 material is fundamental to an understanding of modern chemical structure theory. Includes DAIRY CHEMISTRY AND over 300 pages of computer generated PHYSICS images. Visit the Wiley Exhibit at the Robert Jenness & Pieter Walstra approx. 448 pp. February 1984 ACS National Meeting in (1-89703-5) In Press Written by t\ro internationally known experts, St. Louis-Booths 921-929. this authoritative treatise describes the chemical composition and[properties of milk and its physical structures. Examines the biosynthe- COMPENDIUM OF ORGANIC sis and secretion of miik, the components of SYNTHETIC METHODS, Vol. 5 Order through your bookstore or milk including carbohydrates, salt, lipids, fats, Leroy G. Wade, Jr. write to Nat Bodian, Dept. 4-1744 and proteins, and methods for analyzing these components. Tables and graphs used Presents the new synthetic methods for prepa- extensively. ration of monofunctionaf compounds for 1980, 1981, and 1982. As in previous volumes, sec- FOR BOOK ORDERS ONLY approx. 500 pp. March 1984 tions correspond to most of the possible inter- CALL TOLL FREE (1-09779-9) $59.95 converslons between the major functional groups. In addition, Hits volume contains Save 10% over individual volume examples of new methods ol preparation of 1 (800) 526-5368. prices: difunctional compounds formed into pairs of the major functional groups. In New Jersey, call collect COMPENDIUM OF ORGANIC 552 pp. January 1984 SYNTHETIC METHODS: (1-8672&4) $37.50 (201) 342-6707 order code #4-1744 5 Vol. Set Edited by I.T. Harrison and S, Harrison CHEMISTRY AND ECOTOXICOLOGY OF volume 1, I.T. Harrison & S. Harrison 529 pp. 1971 (1-35550-X) $36.95 POLLUTION \felume 2, I.T. Harrison & S. Harrison D.W. Cormeil & Gregory J. Miller 437pp. 1974 (1-35551-8) $31.95 Describes and analyzes the distribution and WILEY-INTERSCIENCE \feiume 3, L.S. Hegedus and t.G. Wade mechanisms of chemical pollution and its a division of John Wiley & Sons, Inc. 495pp. 1977 (1-36752-4) $31.95 effects on aquatic and terrestrial environ- 605 Third Avenue, New York, N.Y 10158 V3lume4, LG. Wade ments. Includes chemical physical process of 497 pp. 1980 (1-04923-9) $32.50 pollution, deoxygenation, and eutrophication, In Canada: 22 Worcester Road *iume5, LG.Wade thermal pollution, and pollution monitoring. Rexdale, Ontario M9W1L1 552 pp. 1984 (1-86728-4) $37.50 approx. 400 pp. February 1984 Prices subject Io change and Higher in CanatJa. Complete 5-VblumeSe! (1-80966-7).. .$155.00 (1-86249-5) $40.00 092-4-1744

Circle No. 28 on Readers' Inquiry Card Volume 61 Number 3 March 1984 A8i The New Mettler AE100. Just the capacity I need at what I can afford. 20 rnA currtinl I

Now there's a Mettler electronic analyti- pouring speed until the target weight output option and your AE is ready to cal balance for weighing 100 grams or is reached. transfer information. less. The new AE100 joins the higher Because it's so easy to use, weighing capacity AE163 and AE160 analytical on an AE goes three or four times faster Scaled down price. introduced last year. It has the same than on a mechanical balance. And Like other AE balances, the AE100 is big features of the other Mettler AE's, with much more accuracy. It even designed with a simplicity of circuitry And at a smaller price, jyst $1995. adjusts itself to environmental changes that keeps the price down. About as that would throw off other balances. affordable as a mechanical, For more Greater productivity with less effort. information write to Mettler Instrument The AE's foolproof single control bar Data processing. Another Corporation, Box 71, Hightstown, NJ design makes it easy to operate. A sim- big advantage. 08520. Phone (609) 448-3000. ple touch on the bar does most of the The AE has another great advantage work for you. From locking in tare to cal- over mechanicals. The ability to inter- ibration. And the exclusive DeltaDisplay * face with computers and other peri- automatically adjusts itself to your pherals. Just snap on a Mettler data TfUUZUUL Circle No. 30 on Heade'S' Inouiiy Card /cifety in the edited by MALCOLM M. RENFREW University of Idaho chemkoS Moscow, Idaho 83843

Experiments Integrating Evaluation of Chemical Hazards into the Chemistry Curriculum

J. T. Pierce, S. M. McDonald, and M. S. Scogin University of North Alabama, Florence, AL 35632

One way of making students aware of the As much as possible we use experiments that Traditional industrial hygiene sampling need for regular monitoring of laboratories is have been evaluated by the National Institute has relied upon the use of small sampling to offer an introduction to the science of in- for Occupational Safety and Health pumps that could either be attached to a dustrial hygiene as part of the chemistry (NIOSH). The methods described here are worker or placed in an area of interest. Such curriculum. Although laboratory safety and designated by NIOSH as P & CAM 127 {or- pumps individually cost several hundred industrial hygiene may be discussed in a va- ganic solvents) and S4 (hydrogen sulfide). dollars but are sometimes available on loan riety of laboratory settings, opportunities for References from NIOSH outline the pro- from a local industry. Those pumps selected students actually to sample and analyze cedures for both sampling and analysis of should be capable of delivering air flowrates contaminants are rare. We propose the use of hydrogen sulfide and organic solvent vapors as indicated in references (1-3). In this work two experiments tJiat demonstrate important in air, as well as many other substances {1-3). we used Du Pont Model P-30 Constant Flow points concerning the desirability and the Vendors' information may also be useful, Samplers. Pump calibration is easily ac- mea»s of regular iaboraUiry monitoring. particularly technical bulletins {4). Should complished using an inverted buret in the During the past year we have undertaken difficulties arise concerning the availability form of a "soap bubble" calibrator in line as to monitor our own laboratories and have of equipment or the interpretation of refer- shown in Figure 1. Further information on sponsored senior industrial hygiene projects ences it is likely that an industrial hygienist flow calibration is sinnmarized in common directed to that end- We feel that these ex- in the area wiil be able to assist. Organizations references (5, 6). in our work the hydrogen periments have broader applicability and that can provide the names of local industrial suifide was collected as cadmium sulfide may be used as "whole class" experiments. hygienists include the American Academy of when laboratory air was impinged in a cad- Two promising areas for monitoring ap- Industrial Hygiene (certified industrial hy- mium sulfide solution. Arabinogalactin peared to be the estimation of hydrogen sul- (Sigma Chemical Co., St. Louis, MO) was fide levels in the general chemistry laboratory added to the impinger solution to prevent the during qualitative analysis and the determi- decomposition of the cadmium sulfide col- nation of the concentration of organic vapors lected. It may be possible to use inexpensive associated with organic chemistry laborato- plastic impingers for this application (Cole- ries. Parmer Co., Chicago, IL). The collected sulfide was spectrophotometrically determined One of the problems that besets those using a methylene -blue- type reaction (N, charged with laboratory monitoring is the (b) N-dimethyl-p -phenyienediamine and ferric "selection" of suitable analytes given the chloride solutions). large number of candidate materials. Given limited time and resources it may be desir- Activated-charcoal-filled tubes were used able simply to select a few representative for the collection of organic solvents. Care contaminants during preliminary atages. should be taken to insure the air makes con- With the advent of microprocessor-controlled tact first with the larger of the two charcoal gas chromatography the ability to monitor sections of these adsorbent tubes. After large numbers of gases and vapots is en- sampling these tubes were opened, and the hanced. The methods we have selected allow first charcoal layer was deaorbed and ana- the students to perform the sampling and Personal lyzed, A gas chromatograph equipped with analysis themselves relatively inexpensively. Somptins flame ionization was employed. A variety of Pomp columns suitable for common organic materials may be used and an electronic integrator Figure 1. Calibration of impingsr (a) and adsorbent aids the analysis. Since this was a quantita- tube (b). tive form of gas chromatography the solvent Hush technique was employed as shown in Figure 2. The laboratory's ability to carry out such analyses proficiently may be checked by a proficiency analytical testing program such as the one currently carried out by NIOSH; J. T. Pierce is an associate professor of in- samples are sent quarterly and results must Oustria! hygiene ai the University of North gienists) and the American Industrial Hy- Alabama, and S. M. McDonald and M. S. giene Association (both at 475 Wolf Ledges Scogin are senior Industriai hygiene stu- Parkway, Airon, OH) and the American dents. Conference of Governmental Industrial Hy- gienists (6500 Glenway Ave., Cincinnati, OH). (Continued on page AS5)

Volume 61 Number 3 March 1984 A83 pH ELECTRODE

STUDENT PROOF? . . . WELL, ALMOST! CATALOG OF SAFETY • ITS pH RESPONSIVE GLASS BULB IS RECESSED INTO EQUIPMENT ITS 1/16" THICK EPOXY & SUPPLIES BODY SO BREAKAGE IS MINIMIZED. ITS SEALED, GEL-FILLED The nation's most complete source of safety equipment and REFERENCE NEVER MODEL NEEDS REFILLING. supplies for the protection of S200C people, facilities and the COMBINATION environment. Let our experts NO PERFORMANCE pH ELECTRODE SACRIFICE; FAST 12mm DIA BY help you select the products to FULL RANGE 150mtn LONG meet your safety needs and NERSTIAN $40 regulatory requirements. RESPONSE When ordering specify Type of connector or make and mode] To BB' your >rBB c°py. of pH meter circle (he reader's service number or call /'i " lleei Seaboard Circle 906BO USA TELEX714095-434: 1S3124 3

1 Ciickt No. 21 on Readers inquiry Card . 16 on Readers' Inquiry Card

Mandelkern's An Introduction to Macromolecules is now

better than ever.

AN INTRODUCTION TO An Introduction to Macromoiecules offers up-to-date knowledge on the basics of polymers, knowledge MACROMOLECULES relevant to many areas of science, technology, and Second Edition industry—and everyday life. Leo Mandelkern, Florida State University, Professor Mandei kern's An Introduction to Tallahassee Macromoiecules can help make teaching that From reviews of the first edition: introductory course easier, and more interesting for "The overriding quality of this book...is the com- both you and your students. ...We'd like you to bination of concise treatment and lucidity of consider it for class adoption. Your request should exposition...(It is) exceptionally good reading..." be on department letterhead, and should contain —Journal of Chemical Education course title, enrollment, current text, and the date by "A thorough delight..." —ASM News which you must make your text decision.

Once again, Professor Mandelkern provides students Order your examination copy now. with an excellent introduction to the properties and 1983/161 pp. /! 16 illus./paper $16.95 functions of all classes of biological and synthetic 0-387-90796-3 macromolecules.

New York Berlin Heidelberg Tokyo Springer-Verlag ]175 Fifth Avenue, New York, New York 10010 Attn: Susan Paul

Circle No. 29 on Readers' Inquiry Can) A84 Journal of Chemical Education values for hydrogen sulfide1, do not indicate Literature Cited overexposures, and, although other studies (1) "N1OSH Mama! of Analytical Methods," Vol. I, 2nd /ofety of academic laboratories have shown similar ed., 1977. results (7), inter-laboratory variation pre- (2) "NIOSH Manual of Analytical Methods," Vol 2, 2nd vents meaningful geaeraiization. ed, 1977. (3) "NIOSH Manual of Sampling Data Sheets," 1977. Our laboratories were equipped with two (4) Vendors' information; Du Pont Occupational and En- 6-ft fume hoods which were not used during vironmental Health Products, Wilmington, DE; Su- this work. We have since installed individual pelco, Inc., Bellefonte, PA. CSB flush air (5) Brief, R. S,, "Basic Industrial Hygiene," Exson Corp., work station exhausters ao that each student New York, 1975. has access to ventilation. (6> "The Industrial Environment—its Evaluation and Although the specialised nature of labo- Conteol," National Institute for Occupations! Safety and ratory environments makes the application Health, 1973. {7) HerUein, HI, F,, in "Analytical Techniques in Occupa- of Occupational Safety and Health Admin- tional Chvmistiy," Anieitcan Chemical Society, Wash- istration standards awkward, it is still in- Figure 2. Solvent flush technique. cumbent upon laboratory managers and educators to provide a healthful environment for learning. The experiments we have discussed not only provide useful data for as- 1 Editor's note: this high concentration of be returned within fifteen working days. sessment of risk but may also instill an ap- H2S demonstrates the need for caution when Selected results from our work are shown preciation of the possible presence of airborne using thioacetamide outside of a fume hood, contaminants. in the table. These results, excepting the (M.M.E.)

Resulls of Monitoring Contaminants in Academic Laboratories

3 Type Conditions Location Time (m) Volume (m ) Weight (mg) TWA" Contaminant TLVOB

Personal Benzocaine preparation Organic teaching lab 180 0.024 <0,126

Area Thloacelamlde generation General chemistry 15 0.001 5.13 2465 H5S 21 ofH?S teaching lab (short-term exposure limit)

' Vaaws measurBd suprassetl as Hme-ivBiBfttBd averages (mg/rrr5). B 3 S Threshold Limit Value* expressed as ttme-wetghted averagea (mg/m ) (TLVH ifcreshoSd Umit Values for Chemical SulstHnces and Physlca! Agenfs In ths Wo* Environment (or 1983-84, Amarican CojifBtenoa of GovammBntal industrial Hyaienteis). Have you triid these handy <&*> lad aids?

LEAD DONUT THERM-O-WATCH to stabilize tippy the multi-purpose controller abware for temperature, pressure or liquid level

LEAD BRICK tos".ibiiize tippy ringstands and a variety of GLOVE-BAG for work LAB-GUARD with air sensitive materials Safety Shields

1 NAME I I ORGANIZATION- I Getyour | I I ADDRESS .„ I CITY- STATE ZIP I

108 FRANKLIN kVENBE f PHONE Instruments for Research and Industry CHEtTB(H*lt.P*.tSO!! I {215)379-3333 Circle No. 1D on ftsadgrs' Inquifj Card Volume 61 Number 3 March 1984 A85 Announcing the Revision of a Best Sefler! SACJNDERS GENERAL CHEMISTRY, Second Edition HAS THE and GENERAL CHEMISTRY WITH QUALITATIVE ANALYSIS, Second Edition FORMULA By Kenneth W. Whitten and Kenneth D. Gailey, both of The University of Georgia, Athens This best-selling text (used by over 100,000 students FOR nationwide) for engineering and science majors is again available in two versions. General Chemistry, Second Edition, provides balanced coverage of descriptive SUCCESSFUL chemistry and principles, with an emphasis on descriptive material. The Qualitative Analysis version offers clear descriptions of procedures, reactions, and equilibria for the qualitative analysis laboratory. CHEMISTRY Standard Version — Available 1984, 880 pages {approx.), hardcover. ISBN 0-03-063567-5 Qualitative Version — Available 1984, 992 pages {approx.!. hardcover. ISBN 003063827-5

Introducing a NEW Principles-Oriented Text by a Highly Successful Writing Team...

PRfNCIPLES OF CHEMISTRY By Raymond E. Davis, University of Texas, Austin, Kenneth D, Gaiiey, and Kenneth W. Whitten, both of The University of Georgia, Athens This principles-oriented general chemistry text for engineering and science majors offers lucid, detailed explanations of basic concepts, abundant illustrative examples that are-solved and explained in detail, and a wide selection of carefuily graded end-of-chapter exercises. Descn'ptive chemistry is introduced early and integrated with principles throughout, Available 1984. 928 pages (approx..), hardcover. ISBN 0-03-060458-3

An all new Laboratory Manual... EXPERIMENTAL GENERAL CHEMISTRY By W.T. Lippincott, University of Arizona, Devon W. Meek, The Ohio State University, Kenneth D. Gailey, and Kenneth W. Whitten This comprehensive laboratory manual contains thorough descriptions of underlying concepts plus an excellent balance of 36 principles-oriented and descriptive experiments, The book comes with its own Instruc- tor's Manual and can be used with any chemistry text. Available 1984, 416 pages {approx.). hardcover, ISBN 0-03-060463X

A86 Journal of Chemical Education majors alike, the principles of physics, biology, and chemistry that underlie environmental phenomena. OTHER Drawing on the comments of users and reviewers, the authors have rewritten three-quarters of the text and reorganized its content, expanding the book by six QUALITY chapters. Available 1984. 560 pages fapprox.). hardcover. ISBN 0-03-069482-5 TEXTS CHEMICAL PRINCIPLES, Alternate Edition By William L. Masterton, University of Connecticut, FROM Emil Slowinski, Macalester College, and Conrad L. Stanitski, Randolph-Macon College Maintaining a slightly higher level of presentation than SAUNDERS the standard Fifth Edition, the Alternate Edition presents a steady flow of chemical principles with an emphasis on 1NTRO1XICTION TO CHEMISTRY theory. The text is clear, concise, and logical allowing By William L. Masterton, University of Connecticut, and students to read and understand the material. Features Stanley M. Cherim, Delaware County College include approximately 1,300 end-of-chapter problems This book is written for the student taking a one- emphasizing real-life applications of chemical principles, semester or one-term course in preparation for the year and worked-out examples, each one immediately fol- course in general chemistry. Assuming little or no pre- lowed by a parallel exercise. The text also features an vious background in chemistry, it combines a clear, optional section on descriptive chemistry presented lively presentation with a wealth of illustrative learning within the context of qualitative analysis. aids. The authors emphasize systematic methods of 1983, 791 pages, hardcover, ISBN 0-03-062726-5 problem solving by including practice exercises, sample problems and worked-out examples in every chapter. CHEMISTRY, MAN AND SOCIETY, Fourth Edition Available 1984. 480 pages (approx.). hardcover, By Mark M. Jones, Vanderbilt University, David O. ISBN 0-03-069458-2 Johnston, David Lipscomb College, John T. Netterville, Williamson County Schools, and James L Wood, INTRODUCTION TO GENERAL, Resource Consultants Inc. ORGANIC AND BIOCHEMISTRY A comprehensive, up-to-date text that demonstrates By Frederick A. Bettelheim and Jerry March, both of the importance of chemistry in students' daily lives, while Adelphi University developing the science of chemistry and its applications This new text teaches principles of general, organic on a non-mathematical basis. The text features ample and biochemistry in a manner easily accessible to non- illustrations, seif-tests, marginal notes throughout, end-of- majors — especially students of health science. A dear, chapter questions, and end sheets that give the 25 most concise presentation examines the chemistry of the used chemicals and the periodic table, with atomic human body. Numerous problems at the end of each weights and numbers. chapter and worked-out examples in the text enhance 1983, 600pages, hardcover, ISBN 0-03-062716-8 the Seaming process. More than 150 boxes supplement the theoretical material to show students how chemistry affects health care. Available 1984. 73b pages (apprax.), hardcover. HOW TO ORDER: ISBN 0 03 061548-8 For examination copies, please contact your local Saundef s College Publishing sales representative or write on your college letterhead to: Karen S. Miaier, Dept SI ENVIRONMENTAL SCIENCE, Third Edition By Jonathan Turk, Dillingham, Alaska, Amos Turk, City College of the City University of New York, with £>OSAUNDER. BoxS 36 COLLEG, LavaltetteE, Hew PUBLISHIN JerseyG 08735 contributions by Karen Arms, Cornell University • This generously illustrated and highiy readable text Include your course title, enrollment, and text currentlyn i use. To presents a clear, comprehensive introduction to environ- expedite shipping, please include the ISBN (International Standard mental science. Throughout, the authors marshal data Book Number) for eachm ite requested. that engagingly illustrates, for science and non-science Si-8/83

Circle Ho. 31 on Readers' Inquiry Card Volume 61 Number 3 March 1984 A87 YOU CHALLENGED US TO MAKE A BETTER TEXTBOOK. WE MET THE CHALLENGE.

Brady & Hoiums FUNDAMENTALS OF CHEMiSTRY is "one of the most improved Second Editions I've seen during 20 years of reviewing first-year chemistry textbooks...a remarkable effort that has resulted in an interesting text with a mainstream content." —John DeKorte North Arizona University

Brady & Holum's FUNDAMENTALS OF CHEMISTRY, Second Edition provides a more thorough, challenging and stimulating approach to general chemistry for science majors than ever before. Yet it's as readable and accessible as ever. A Better Now of Topits Two new, logically developed chapters on chemical reactions—the first, on ionic reactions in aqueous solution; the second, on redox reactions of various kinds • Former Chapter 2 on gases has now been moved back to Chapter 9 • The new sequence of thermodynamics, kinetics and A Complete Learning Patkage equilibrium allows for more logical thematic develop- • Teacher's Manual, Solution Manual, Student Study ment and permits the linkage of equilibrium to A G in Guide, Laboratory Manual, Teachers Laboratory Manual, Chapter 16 on equiSibrium Transparency Masters, plus an all-new Microcomputer- \zed Test Generator for the Apple il Plus/lie and IBM PC, A More Challenging level of Material which offers 500 multiple-choice questions • More quantitative material, including bond energies and • Valuable computer-aided supplements designed to help heats of reaction, integrated rate taws for first and sec- students review chemical concepts and hone their ond order reactions, temperature dependence of rate problem solving skills: Computer-Aided Instruction for constants, calculating activation energies, ionization of General Chemistry by Wiliiam Butler & Raymond polyprotic acids, determination of ion concentrations Hough (both of the University of Michigan) and The from cell potential measurements, and more Chemistry Tutor Balancing Equations and Stoi- • New and more challenging in-chapter worked examples, chiometry by Frank R Rinehart (College of the Virgin practice exercises following the examples, and end-of- Islands) chapter review exercises {0 471-87548-1) 1984 960 pp. Two New PedagogUal Approaches To be considered for complimentary copies, write Lisa Berger, • A progressive approach toward problem solving mat Depl, 4-1651, or contact your local Wiley representative. For features five strategically placed sets of review exer- CAi Information, write to Bill Rosen, Dept. 4-1651. Please cises, entitled Integration of Concepts, which tie include address, course title, present enrollment, and current together concepts discussed in groups of reiated text and supplements. chapters • Chemicals in Use—An innovative addition to topics in descriptive chemistry, featuring 19 two-page discus- JOHN WILEY & SONS, Inc. sions of major chemicals and chemical processes 605 Third Avenue. New York, N.Y. 10158 !n Canada- 22 Woreliester Road located between chapters Rexflale, Ontario M9W 1L1

4-1651

Circle No. 25 on Bandars' Inquiry Card A88 Journal of Chemical Education topic/ in edited by FRANK A. SETTLE, JR. Virginia Military Institute chemical in/trumentotion Lexington. VA 24450

Choosing the Right Instrument: The Modular Approach Part II

Howard A. Strobel Duke University, Durham NC 27706 Instrument Specifications: Which Modules Determine What? In Part I (which appeared on page A53 of the February issue) the rooduiar approach to Table 2. Modular Clusters In Representative Instruments instrumentation was described as an effective way to ease the process of selecting an ap- Modules in Modules In propriate instrument for a particular mea- Generalized UV-VIS Modules in surement as well as to develop an under- Instrument Speclrophotometer pH Meter standing of an instrument's behavior that would lead to its more effective use. Further, Signal (Continuous source) pH eeli with attention was directed to the characteristic source iMonochromator I reference and giass cluster of modules at the "front end" of an Cluster of electrodes instrument as those to study in reaching a Characteristic Sample Sample eel! {self-source. decision about which instrument to buy or Modules module sample celt. use for a determination. How well can we re- and late instrument specifications, which repre- Detector Photornultlpller detector) sent a major part of the data furnished for tube review by a prospective user or purchaser, to Cluster ot Amplifier \ Amplifier / Amplif ler the behavior of modules? Or to put the Processing question more sharply, how often is a speci- Modules Signal processing >I Processing { Processing fication fixed by a single module? Since we modules 1 modules I modules shall now look critically at these matters, in Readout / . Readout V Readout

Reference Character- istic Continuous Chopper ^ ^ Detector- cluster source Monochromator and beam transducer splitter Sample

Computation Photometric Readout module (ratioing) module

Figure 4. Line diagram of modules of a double-channel spectropholometer.

Table 2 the terms characteristic cluster and their instruments so that no module will limit modules, the separate channels are appro- processing cluster are defined and illustrated performance as the "weakest link in the priately rejoined. One such arrangement is by application to a spectre-photometer and chain." shown schematically in Figure 4. The two pH meter, A detailed analysis of the charac- Even where the design departs from the different signals failing on the detector are teristic modules of each will be given single-channel pattern, as in double-channel "sorted out" in the processing modules and below. instruments, the modification is usually a compared. As is evident from Figure 4, the To tackle the queries about specifications minimal change. For instance, to construct characteristic cluster of modules is essentially effectively, we need to insure that complex- most double-channel layouts, a sii^le-chan- unchanged. The chopper becomes part of the ities of design which are beyond the scope of nel instrument is opened up at the sample processing set of modules. tills presentation can be ignored. Fortunately, module. Usually a chopper which alternately Most other changes in design have to do most instruments, like the one in Figure l.are directs the "signal" from the preceding with impositions of automatic control. For of single-channel design. For these instru- module to a reference-cell channel and sam- ments we shall assume that manufacturers fjJe-cell channel performs the function. Im- are employing modules of equal quality for mediately beyond the reference and sample (Continued on page A90)

Volume 61 Number 3 March 1984 ASS in/trumentotlon rangeimportan, precisiot of thesn oef arwavelengte likelyh to setting be wavelengt, spectablisTh-heh spectra the maximul rangme of wavelengt the sourche rang wilel o alsfo the es- absorbancetral slit widt, hstra (resolution)y light, an,d precisio scanninn gin speed %Toinstrumentf. th oer rang.e Wher or ae stilhighel greater intensitr rangye in is par desiredt , addeexampled to, a stabiliz feedbacek th eor outpu controtl o loof apn wa opticaythesWha bleet instrumen connectiont sspecification can wes anmakd ethos betweee fochoicadditionarne isl madesource,s th wile loutpu be requitedt of the. sourcWhatevee musr t modulsourcee. Tharee uisaffeetedgeneral ;characteristic the feedbacsk o loof thpcritericonstituene a seetm modules to fal?l Othein thre performanc processinge catechromatobe- focuserd fo orn goo thed entranccouplinge. slit of the mono- insures that fluctuations in output are minigory- : they are factors such as scale expansionTh,e monochromator is next. The wider its putemizedr .contro A similal as rwil resull bet isdiscusse securedd later with.oreadou comf analyte-t in, anabsorbanced availabilit, %T,y of firs to ran concentratiod seconentrancd ne and exit slits (widths are usually To examine the degree to which instruderivatives- . precisioequal),n th ine %T. greater th Aes S/N is wel lrati knowno and, ' inthe a omenf individuat specificationl modules derivse w froem ca nspecification considersturn iLen.t Thuse tak firset th ise th characteristie continuouc smodule sourcesamonoehromato .int the expensre a o fbette resolutionr S/N. Th ratieo wide is gainer itsd twsomoe instrument detail thes pardetailet played ind Tablby modulee 2. Fosr stanClearlyin th thete it,s th outpute mor,e th eintens greatee anr dthe th signai/noise more anslitsconed,- thu thes greatethe poorer alsor it is resolutionits spectra.l Th slite width specificationUV-VIS spectre-photometers will be of interest, a lon. gTh elis tmos cisio(S/N)oftn in %T ratio ofr thabsorbance spectrophotometere will be enhanced:persinqualit pre-yg. elemenand sizte (usuall of thye a monochromato grating) andr optic dis-s wilficiencl alsyo an ddirectl reducye enhanc the levee resolutiol of strany an lighd tef -(at wilthel fixexit th slit)e resolution. In essence, S/N, the ratio monochromato, and leverl of See these and other titles at Booth 836 rangstraye light provide. Itd ma byy th alseo sourc reducee an thde thu fulls spectra fix thel during the ACS convention! range practically available. NEW! theWha samplint of gthe modul othere characteristi and detectorc modules? In th,e £Introductio Russdi Hardwick,n to Chemistry UCLA. Emphasizing a problem solving approachcuvettsimples, thiest o thorougcasr ecell hth.e texCell samplints give thasgt modulhold esampl wilel b aned a piesa detaile, exercised introductios andn problem toth es fundaments are used) t oconcept helps student and theories understans ofd beginnin the basig cchemisby concept.s anreferencExam andd -transmissio hoew shouldn b characteristicse matched in. Apatsh Fai lengtt Ih Bythey, an cadn nucleabe applier chemistrd toy th eare chemica Includedl world. Januar. Separaty 1984,66e chapter8 pagess on, iHua organi, clothc chemistry. Supplementa, remindebiochemlsl d- us, coupling between modules materials: Insbuctor's Guide, Student Study Guide, Transparency Masters. thshoule outpud facilitatt ofe th ethe detecto passagre goe ofs signal to the. Sinc traine of Fourth Edition processing modules, the detector must not Chemistry for Changing Times froonlmy threspone sampld toe thbuet alsintensito transducy of ethe it to signa anl chemisayJohn, an W.d applie Hill,s them toUniversity everyday fife.H' s writte onf Wisconsin in a relaxed, conversationa • Riverl stylacteristicelectricae with Falls. las output of detector. Thi Somss successfue ar othee higlr htexdesire tsensitivity coverd schar the,- principles of chemicaminimuml wastes of technical, the jargonuse o.f Ne thwe mol materiae Inl ochemican lisksl ancalculationsd benefit,s ari odf scienca newe an chapted technologyr olonw "Sports ,noise:, and a short response time. Materials.The Chemica* instructor'l Connection.s Guide"; StudenFourtht Editio Studyn GuideJanuar;y Laborator 1984,57y6 manua pagesl, illus.- Chemica, clothl. SupplementaInvestigationmultiplieBeforsler considerin tube usegd ihonw the wei spectrophotoml the photo-- foBanr kChangin - ag se tTime9 of 45, 0Fourt multiplh Editione choic, bey Items Lawrenc; neew W Transparenc. Scott, yJoh nMaster Ws. Hill- a, ansedt o Petef 20eter0 Mutor of; Tabl Teste 2 meets these requirements, let master sheets. sponsus looek to a tligh itt a sas a na functioopticanl detector of wavelengt. Itsh re- General, Organic, and Biological Chemistry: Foundations of Life will be multiplied by (convoluted with) the DM Felgl, SL Mary's College, ffofre Dame, Indiana.frointensitm thye versu source-monociironiator-sampl J.W.s wavlengt Hill,h functio nUniversity available celle ofWisconsin - Rioer presentFails.s the Writtebasicns forof thchemistre 'shorty 'in Introductor an integratedy cours,e coheren for nursint mannerg and, i healt 983h, 38scienc4 pagese majorscombination, iBus., thi,s tex.t By choosing a photomuitiplier doth. Student Study Guide and Instructor's Guide available, availabletube wit,h goo thde sensitivit broadesyt ospectraf detectiol responsn is ine- Chemistiy and Life: An Introduction to Genera!, Organic, and Bio-sured from 190 nm to beyond 800 nm. The logical Chemistiy higher its gain and the lower its noise, the J.W. Hill. DM Feigi Appropriate for a fulhyear chemisby majors courseconcentratiobette,r thi sthe textn possibilitgive levelss a.y balTh -oef workindetectogr ahats trac the tionanced an doffer integrates medicad presentatiol and biologican of generall applications, organic, an, dand stud biologicay aidsl. chemistrySecond Editio. Thne secon1983,77strongesd 3edi -pagest influenc, e on the limit of detection Sllus., cloth. Student Study Guide and Instructor's Guide available. surementof measurements will .als Dynamio depencd aspect stronglsy of o nmea th-e Second Edition detector. If the spectrophotometer must scan Chemistiy and life in the Laboratoiy: Experiments in General, rapidly, the detector must have a fast re- Organic, and Biological Chemistiy sponse. V.L Heasley and VJ. Chiistensen, both of PointcleaWhar picturt Lamaise gaine thadt froth College.me mai then brie opticaf analysil Q£. specifis is- Heasley, a Bethany estNazaivnes and careers In College. nursing, and healt hTh eand 33 life experiment sciences.s Secon in thids Editiomanuanl 1963 are, designe 264cationd pages to relats, illus.oef ttho,e students UV-VI'S inter spectrophotomete- r in paper. Instructor's Guide available. ifact bty result itsfro characteristim the performancc modulese "buil. Onlty into if" the Laboratory Methods in Organic Chemistry performancsubsequente module will thse caus instrumene deterioratiot as an whol ine laboratoiS. Marmor,y program. The California first experiments are presente Slated (Jm'uersfli with detailej - Domingued step bzy Hills. step instructionsfai Thil tos. tex livte offer usp a to class-tested this "advanc, flexiblee billing." Graduall1961,56y7 studeni pagess, illus. are, required doth to. Instructor'desig ns mor Guidee of available the step.s in the experimental proceduresmoduleTowar. ds thwilel enalsdo obfe th examinede section., its process To order your complimentary copy- ptease contact: surprisinglThe modulay simplr diagrae asm show ofs th ien pTablH emete 2.r In is- f~ir\ Burgess Publishing Company yieldspectiosn th eof resul the ttabi thaet an itds characteristiits performancc emod als-o t D ) 7108 Ohms Lane, Minneapolis, MN 55435 ules determine the specifications of the LV (612)831-1344 overall instrument The ceil is simultaneously (Continued on page A92) Circle Mo. 4 on Readers' ln

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Circle No. % on Headers' Inquiry Card Volume 61 Number 3 March 1984 A93 of individual modules even in sophisticatedinterferences reduce the ability of an instru- In/trumentotlon instruments. ment to resolve signals from substance of The gains in having a microcomputer ininterest an , or whenever the number of species instrument are those already suggested andin samples increases, upgrading the sampling are well known to readers: greater ease, modulpre- e in some way will be necessary. Recall cision, and flexibility in use of an instrumenthatt what may be termed extra-instrument and improved efficiency of data collectionmethods such as extraction of a substance of way that the S/N of the beam fallinangd o processingn . We will want also to consideinteresr t into a favorable eofvent have long sample and reference calls is constant these gains when reaching decisions about usbeeen employed and are still available for with wavelength. By such means autoand- purchase of instruments. sample preparation. Where an instrumental matic completion of a measurement is or- solution is desired, chromatographic systems dinarily assured during unattended oper-The New Hyphenated Instruments and devices such as mass spectrometers now ation. Is the modular approach applicable when offer their versatility, ease of use, and effi- an instrument has a plethora of modules? In ciency for "sampling." It is clear that this 3) Computer Operationthe pasandt few yearControl.s increasing numbers of answer is attractive since hyphenated in- ' For nearly complete control and automacoupled- , or as Hirschfeld has termed them, struments are appearing in increasing num- tion one or more microprocessors {micro"hyphenated- " instruments (7), with almost bers in research and other laboratory set- computers) is wired into an instrument tings. (or connections are made to a minicomtwic-e the usual numbers of modules have puter). Nearly always programs for operappeared- . The first widely used hyphenated ation are entered by the manufacturerinstrument may have been a gas chromato- By application of insights from a modular into the read-only memory associated graph-mass spectrometric {GC-MS) device, analysis we see clearly how great is the con<- with the computer. The programs includbuet MS-MS, LC-MS and many other coupled tribution of this new class of hyphenated in- provision for the user to interact will) thinstrumente s have since been developed. steuments in enhancing analytical power. For computer. According to the program Consideration of one of these apparently a more complete discussion of these devices called up, a microcomputer prompts thcomplee x instruments seems worthwhile to the reader is referred to Hirschfeld's paper user to supply information about the kindemonstratd e the- general validity of the (7). of measurements to tie made and themodular approach. Conclusions samples. The program indicated by theseIt proves helpful to begin by asking where data provides for appropriate operationthe instruments are joined. Take the GC-MS To understand the relative advantages of of modules and data acquisition. Subseas- a representative example. Its layout is different instruments it is valuable to be able quently the user, or more commonlysketche, a d in line-modular form in Figure 5. to view them as modular systems. Such a view second built-in microcomputer or a laboNot- e that the output of the GC is the input of calls for a qualitative knowledge of (1) the ratory computer processes the data anthde MS. We can conclude that the GC re- types of modules that comprise roost instru- extracts desired enejnical information. solves samples into their components and ments, (2) the performance characteristics of that the MS produces the spectrum of each representative modules, and (3) the close of these in turn. Since the ability of the Some redesign of an instrument will, of correlation between the specifications for chromatograph to separate components is modules in the characteristic cluster of in- course be required to effect computer controlclearl. y being exploited, is it not reasonable to struments and those of the resulting instru- Sensing devices such as position encodersuggess t that it is functioning here as a state- must be inserted to furnish data to the comof-the-ar- t sample module for the mass spec- ments. With this background, users of puter. Devices that the computer can actuattrometere ? Perhaps "sampling module" would chemical instrumentation can ask appropri- such as stepping motors must also be added ate questions that will help them reach de- Carrier gas Controlled source Sample Separation : of carrier gas injection column diverter ~\ port Vacuum system

Processing Mass lonization Detector Readout module analyzer source i i i i

Figure 5. Line diagram o! modules ot a GC-MS hyphenated instrument. to allow program control of scanning and be a name more descriptive of its role in this cisions as to which instruments to use, buy, other operations. A good account of the de- example. Can we describe the role of a sam- or lease for particular measurements. velopment of a sophisticated instrument with pling module? For a UV-V1S spectropho- The range of instruments examined program control was given by Barnard (6). tometer, for example, we begin by stating that should, of course, reflect kinds and number We return to the query: How does the ad- the sampling module holds the sample solu- of measurements to be made, the types of dition of microcomputers affect instrument tion. But even the dissolving process can systems to be examined, and the level of ex- performance? For an answer let us look both usefully-be regarded as "part" of the module. perience of persons who will use the instru- at the characteristic and processing clusters Indeed it will need to be so considered ments. Vet within that range the simplest of modules. In the characteristic cluster whenever dissolving or diluting is mecha- instruments that have the desired sensitivity, currents, slit widths, etc. will now be set by a nized, which is likely to be increasingly the accuracy, and operating features will be the computer program instead of the user or case with sophisticated and sensitive instru- best choice. There will be fewer parts to give manufacturer. In the processing cluster the mentation. The trend is certainly toward trouble, spurious instrument responses will microcomputer will take the place of several performing a greater number of operations on be more easily noted and traced to their modules. Important gains in processing per- samples in instruments themselves. source with greater ease, and maintenance formance will result (in signal massaging, will be simpler and less expensive. UsuaEy data collection, and computation). Even in Yet a still sharper focus on the role of the the initial cost will be lower also. Fourier transform spectrometers a computer sampling module is warranted. Consider the characteristics of an ideal sample. For most To assist in the decision-making process, provides processing by shifting the domain we also gain much by developing a working of signals encoded with analytical informa- measurements it would be ideal to have all "molecules" in the sample well separated to knowledge of widely used detector-trans- tion (from the interferometer in the IR ducer modules, signal-generator modules, spectrometer and from the detector in the insure their separate reaction witli "signal." Further, interfering substances should be and sampling modules. It is these types of NMR spectrometer). Recall that a shift of modules that serve in the clusters of charac- domain, from analog to digital, was already masked or reduced to minimal concentrations to reduce spectral interferences and the kinds teristic modules and that largely determine provided to accommodate the digital micro- instrument specifications. computer. Yet every module will still interact of chemical interferences often termed a with signals through its transfer function and matrix effect. input and output characteristics. Thus, we When will a regular sampling module meet can conclude that instrument specifications these goals and when will we be well advised Literature Cited always depend ultimately upon performance to select a hyphenated instrument with its (6) Barnard,!1, W., Anal. Chem., 52,1172, i state-of-the-art sampling module? Whenever (7) Hiraehfeld, Thomas, Ami. Chem., 62. 397A, (1980). J. CHEM. ED. 801 READERS INQUIRY CARD 1 Please print or type the following clearly: Have you MARCH 1SS4 INITIALS LAST NAME This card CANNOT be processed alter used our SEPTEMBER 1984 TITtE DEPT. Cards with READERS' Incomplete SCHOOL OB FIRM infotmatiort INQUIRY cannot be processed. CARD STREET ADDRESS OR BOX IF USED recently? ^ CITY STATE ZIP CODE (mandatory by P.O.) TELEPHONE NO. It was designed 12 3 4 5 6 7 8 9 10 11 12 13 14 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 42 43 44 45 46 47 48 49 50 to give you 51 52 53 54 55 56 S7 58 59 60 61 62 63 64 67 68 69 70 71 72 73 74 75 8 76 77 78 79 80 81 82 63 84 85 86 87JL I? 92 93 94 95 96 97 98 99 100 better service 101 102 103 104 105106 107 108109 110 111 112 113114 115 116 117118 119 120121 122 123124 125 126 127 128 129 130131 132 133134 135 136 137 138 139 140 141 142 143 144 145146 147 148149 150 161 152 153 154 155156 157 158159 160 161 162 163 164 165 166 167 168 169 170171 172 173174 175 176 177 17B 179 180181 182 183184 185 186 187 188 189 190 191 192 193 194 195198 197 19a199 200 The following is a partial list NO POSTAGE STAMP of suggested NECESSARY IF MAILED IN THE abbreviations UNITED STATES you may use in filling out BUSINESS REPLY CARD this card FIRST CLASS PERMIT NO. 21 7 CLiNTON. IOWA

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Circle No. 26 on Readers' Inquiry Card Volume 61 Number 3 March 1984 A97 The chemistry

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Volume 61 Number 3 March 1984 A99 MEZLrTEIMR® The Best Melting Point Academic Press offers experience Apparatus for Less in chemistry. MEL-TEMP" is an integrated capillary melting point apparatus with heating rale continuously controlled by variable transformer. Excellent viewing NEW! CHEMISTRY, Second Edition provided by built-in light and 6-power Bailar, Moeller, Kleinberg, Guss, Casteliion, tens. Attractive sllvertone base is 4"x 5" and includes 6-foot grounded and Metz power cord. This new edition emphasizes descriptive Heats to 500°C. • Accepts chemistry without sacrificing basic principles. One to Three Samples • Rapid Heating and Cooling • No Chemistry, Second Edition, correlates chemical Heat Transfer Fluids concepts with descriptive chemistry, stresses patterns of chemical reactions, and shows only*lWJ P Does not Include m.p. students how to analyze problems with a capillaries or Iriermometer heuristic method that uses dimensional ACCESSORIES analysis as a guidepost. D-SIXfC thermometer in !°C Chemistry with Inorganic Qualitative Analysis, graduations. 76mm. imm. $!2.00

Second Edition, by Moelter et al., is also graduations, borosfcate glass, nitrogen filled, 76mm. imm $15.00 available. Vial of 100 txwosiNcate gtess (ii.9- capiMras 100mm lone, ssatefi one end S3.00

NEW! ORGANIC CHEMISTRY Write tor bulletin 8OA Stephen J. Weininger and Frank R. Stermitz LABORATORY DEVICES P, O. Box 68, Cambridge, MA 02139 Organic Chemistry features an early introduction of molecular structure and its Circle No. is on fteadars' representations. Spectroscopic methods, including 13C nmr, and bio-organic examples, ARE YOUR STUDENT ORGANIC LABS FLAMELESS? treated at the molecular level, are used THERMOWELL - POWERMITE throughout the text. NEW . . . Powermite heat control models SS-4F (top) and EB-1F NEW! STUDENT ORGANIC MOLECULAR are designed for recessed (flush) installations in wall MODELS panels 0.5 to 1.2" thick. Use in new fab construction or in re- Academic Press introduces two sets of modelling old iabs for a neat, molecular models: framework convertible to ball unobtrusive power source. SS-4F (600 w) Is solid state, and stick, and framework convertible to space- EB-1F (1000 w) is an on-off pro- filling. Both sets feature coior-coded framework portional control. Base plate is satin stainless steel. Both are atoms, coSor-coded plastic rods for terminal priced at S47 each. Write for atoms cut to the appropriate length, connectors details. that ailow or prevent rotation, and p!ug-on, Thermowell flask heaters and Powermite heal controls coior-coded, space-filling units of exact scale. are preferred for use in college tabs because of per lor ma nee, durability and increased safety. Our equipment now serves BIOPOLYMER MOLECULAR MODELS over 1000 colleges and universities. Write for our free catalog of molecular models of nucleic acids, proteins, and carbohydrates.

For more information or examination copies, write to Academic Press, College Division, Orlando, FL 32887 or cat! collect r (305) 345-2466. LABORATORV C/=?>CVF TS/VI P O BOX 148, BELOIT. Wl 53511

Circle Ho. 1 on Realtors' Inquiry Card Circle Ho. 14 on Readers' Inquiry Card A100 Journal of Chemical Education out of the editor> bo/ket

JAMES A. GOLDMAN

New Apparatus ami Equipment externally controlled by computers and other working principles, specific features and devices. A microprocessor spectra controller technical specifications of the SORPTY 1750. which can change wavelength and range at The Instrument provides gas adsorption Meter Spectropholometer preset times, as well as store scanned spectra, measurements and specific surface area is available. It allows base-line correction, analysis. The SORPTY 1750 is the only true wavelength switching, spectrum subtraction, single-point BET instrument designed for rou- and plotting after Ihe chromatogram is com- tine applications where results of surface area, pleted. density and cheml-sorption measurements are Circle #42 on Readers' Inquiry Card required within minutes. Circle #44 on Readers' Inquiry Card

Chromatography Integrator Gas Chromatogr aph

A low cost, compact spectrophotometer thai features 8 nm bandwidth, solid state detector and electronics, and a diffraction grating monochromator has been introduced by Se- quoia-Turner Corp. The Model 320 Spectre- photometer has a continuous wavelength range of 330 nm to 1000 nm to cover all routine UV and colorimetric tests. This range can be extended to 210 nm with an easily instaiied Far UV accessory. This wide range is achieved by a monochromator having a plane diffraction grating in.an f7 Ebert mounting. The monochromator utilizes a single casting to maintain alignment of the optics, sample, and solid state detector. Two controls simplify operation and a large analog meter provides easy readability in Absorbance and Percent Transmlttance. Perkin-Bmer's new Model 8300 Gas Chro- Circle #41 on Readers' Inquiry Card matograpfi Is a compact, moderately priced Perfcin-Elmer's Model LCI-100 Laboratory instrument ideal for routine or process labo- Computing Integrator is a low cost chroma- ratories. The system incorporates built-in data tography data handling device. A simple, sin- handling with 12-ln. video screen display and gle-channel chromatography integrator, the post run manipulation of data. Easy inter- LCI-100 offers flexibility in handling reporting change between injector and detector types functions and can teplot and reintegrate Continuously Variable HPLC Detector facilitates the analysis of a wide range of chromatograms. It Is preprogrammed for high samples. The Model 8300 is available in two high speed data acquisition, reduction and versions; the 8310 for packed column opera- reporting. Key features of the LCM00 include: tion; and the 8320 for dedicated capillary ail standard chromatogjaphy calculations (area systems. The Model 8300 provides enhanced percent, area normalization, external and in- performance through such features as auto- ternal standardization), multi-method/multi- mated bleed compensation: real time display peak file storage with 128K bytes RAM, a of a chromatograph; and integral data handling choice of reporting peak height or peak area, facilities. The system is controlled by an ad- run-timed events to customize data handling, vanced microprocessor, with user-interaction a full alphanumeric keyboard, an interactive through the video display unit and simple Liquid Crystal Display, and a full size printer/ keyboard with eight "soft keys." Screen plotter. graphics and integral data handling options Knauer introduces an inexpensive, fuiMeatured Circle #43 on Readers' Inquiry Card ailow the Model 8300 to be developed into a spectra] detector for HPLC. Servo selection complete chromatography and data process- enables wavelength to be digitally set from Ing system. The screen graphics permit a 190-600 nm in 1-nm steps. Perfect for ana- chromatogram to be displayed in real time on lytical and preparative applications, this unit Microstructure Instrumentation the screen and replotted at the end of the run offers a compfementally wide range of cells using variable screen widths and attenuations. Erba Instruments, the U.S. sales and service Hard copy printouts can be obtained by con- from micro to prep. Key front panel features organization of Carlo Erba, manufacturer of include event mark, auto and manual zero necting the Model 8300 to any coventionai pen elemental analyzers, microstructure instru- recorder or to a printer/plotter. At the end of offset, and eleven measuring ranges (from ments and gas chromatographs, released a 2.56 to .0025 A.U. in binary steps). The an analysis, the built-in data handling system brochure highlighting the newest member In can take over to display results in the form of 87.00's design Incorporates a high pressure a family of specific surface area analyzers. flow cell that is quickly and easily exchanged The 6-page publication illustrates how the and cleaned, making occasional cell inspec- classical SET method can be automatically tion quite simple. For automated systems all applied for surface area determinations in & {Cuntinued on page A102) front panel features in the standard unit can be multitude of industries. Described are the

Volume 61 Number 3 March 1984 A101 wait mounted for space savings and accom- every application in the lab or in the field where out of the modate fan-fold paper. reference, standard or combination electrodes Circle #47 on Readers' Inquiry Card are needed. editor > bo/ket Circle #49 on Readers' Inquiry Card Micro Gradient HPLC System X-Y Recorder a peak table and allows post-run manipulation o! the data. Circle #45 on Readers' Inquiry Card

Light Element Detector ft A light-element detecting unit for energy dis- persive X-ray analysis, called Econ III, Is available from Edax International, Inc. Chief features of the new Econ III are: its ability to detect Boron (Atomic No. 5); remote window mesa GXADISST W>J!_SVSTEM change lor standand and light element ranges; and motorized controls with built-in protection Introduced by Houston Instrument, the Series against accidental vacuum loss, failure, or In response to the growing interest in narrow 200 X-Y Recorder provides users with both contamination. Design features of the new bore chromatography, Beckman Instruments, performance and reliability in a rugged and Econ III, based on Edax's seven years of ex- Inc. has introduced the Model 344M Micro handsomely styled low-profile Instrument. perience with Econ ii (the first successful Gradient System. This system is designed to Designed for the working laboratory, the Series "windowiess" detecting system for EDS) in- provide optimal performance when working 200 meets the needs of both educational and clude smaller probe dimension for close dis- with 2 mm HPLC columns. At the center of this industrial users. Reliability is enhanced by tances to the specimen (lor tighter X-ray ge- system is the new Model 114M pump featuring Houston Instrument's proven and patented ometry) and an improved election trapping user-seiectable Mow ranges of 0.001 to 1.00 capactive rebalance position transducer. This design for better noise ratios (for improved mL/min or 0.01 to 9.99 mL/mln, resulting in innovation eliminates the wear and electrical sensitivity). Motorized controls improve op- excellent reprodgcibility at tow flow rates noise associated with slide-wire potentiome- erator convenience and reduce Hkefihood of without sacrificing performance at high flows ters. The Series 2000 X-Y Recorder has 11 error during anaiysis. when they are required. A system organizer switch-selected input ranges starting at 1/ Circle #46 on Readers' Inquiry Card incorporates a iow column dynamic mixer mV/ln., and S timebasa ranges to drive the pen which is designed to blend and mix difficult beam at speeds from 200 seconds/in, to 1 solvent combinations effectively at low flow second/in. A slew rate exceeding 30 in./sec- rates. The Beckrnan range of UV/Visible and ond assures accurate data representation. User Designed Chromatography fluorescence detectors Is available with micro Circle #50 on Readers' Inquiry Card Recorder flow cells for optimal efficiency when used with this system. To complete the package, a range of 2 mm I.D. Uitrasphere columns is now available. Three Channel Flatbed Recorder Circle #4B on Readers' Inquiry Card

pH Electrodes

The Linear Model 595 Flatbed Recorder features three channel recording convenience and a large number of standard features. The Model 595 has 22 chart speeds, 10-in. {250 mm) chart width, 100% zero suppression, and 12 input ranges from 1 mV to 5 V. According to the manufacturer, this full size, sturdy re- Linear Instruments has announced the Model corder also features a remote programmable 1210 simplified, low cost recorder dedicated chart drive and an override event marker as for use in liquid or gas cfiromatography. Nearly standard. Other options are available. 3000 chromatographers were surveyed to Circle #51 on Readers' Inquiry Card learn those features which they wanted most, and least, in a recorder. The results were tabulated and the Modei 1210 was built accordingly. Strikingly simple for high reliability Karl Fischer Tltrator and low price, the Model 1210 Chromato- Curtm Matheson Scientific, Inc., has introduced A microprocessor-controlled, precision in- graphic Recorder features a recessed zero a fine of pH electrodes. These products, named strument for water content determinations, adjustment and front mounted, push button Silver Label pH Electrodes, provide these capable of analysing the moisture range from control of power, chart drive and full scale unique features: Porous Teflon tiquid junction, one part per million to 100 percent, Is an- spans. A convenient manual advance/rewind which controis flow rate, resists clogs, inhibits nounced by Mettler Instrument Corp. The knob permits accurate chart positioning for "poison ion" penetration, and eliminates Mettier DL18 Karl Fischer Tltrator provides parallel or overlay runs. Chart drive speed is streaming potential; Stainless stee) caps; precise water content results with speed and 1 cm/mln, but speeds of .25, .5, 2, or 4 cm/ Low-noise cable; Speciai low-impedence extreme accuracy. The DL13 covers the full mln speeds are available through quick and full-span glass formula; and Patented tech- determination range which, until now, could simple gear changes. The 1210 Is a flatbed nology. Manufactured in the United States, only be done on two different instruments: model using 200 mm width paper, but can be Silver Label pH Electrodes are available for coulometers for trace anaiysis, and volumetric

A102 Journal of Chemical Education available to satisfy virtually any production or soon as it is switched on. In this way, the laboratory requirements. All FTS Bio-Cools warm-up time is eliminated. Automatic cali- feature continuous digital temperature display. bration Is standard. And, in addition to obtaining Three programmer models are available: a weight indications in grams, the balance wili single-segment three-function, a fcxr-segmeftt convert them automaticairy to such nonmetric three-function, and a sixteen-segmeni three units as Ib, oz, ozt, dwt, ON and ct on demand. function. The operator can select one digitally The selected unit of weight lights up in the setable temperature, on ramp rate and one display and the results appear In large seven- hold time per segment. The single-segment segment numbers. Still another feature is the programmer offers as a standard an audible optimized integration of measurement values. alarm which sounds when hold temperature This means that the balance always adapts has been attained. The four and sixteen seg- itself to its environment and automatically ment programmers feature a non-volatile calculates the optimum integration time. memory which win store a program for up to Circle #54 on Readers' Inquiry Card six months without electrical power. Ail pro- 1 grammers include an analog voltage output to facilitate future connection of the Bio-Coo! lo a temperature recorder, FTS supplied or other. HPTLC/TLC Developing Chamber The FTS line of Bio-Coo! Controlled Rate Freezers can do it aft: from the most basic on-site regimen to the most stringent laboratory protocol. All have the convenience, reli- ablity and low-cost that only FTS can offer. Circle #53 on Readers' Inquiry Card titrators tor high water content. Operation of the DL18 is quite easy; it is carried out via a "pushbutton dialogue" with the operator. Solvent dosing and evacuation of effluent are Laboratory Balances activated simply with a posh of a button. The result is determined automatically In percent, ppm, or mg of water. Many extras such as *ift compensation, freely selectable stirring time and blank value correction are all standard. The same precision burette that is well-proven An advanced-design Developing Chamber for with Mettler's DL40RC MemoTitrator is also high performance thin layer chromatography standard. By connecting the DL18 to a Mettler (HPTLC) and conventional TLC plates has been analytical balance and GA44 printer, conve- announced by Advanced Separation Tech- nience and reliability can also be increased. nologies Inc. (Astec}. Designated Vega-T 10X Sample weight may be accepted automatically Developing Chamber, the unit is precision and used for final calculation purposes. The manufactured of white FIFE with a laboratory printer will provide a complete record of re- glass cover. Adjustable leveling legs and an suits including date and sample number. The Astec ACCUFLAT levei ensure linear solvent Karl Fischer method of determining water fronts. HPTLC and TLC plates developed in the content Is a procedure that has a permanent Vega-T10X Chamber have exhibited excellent place in today's laboratories. Food, chemical Rf reproducibility in tests at a leading university and pharmaceutical manufacturers all need and in the field. Uniquely, the Vega-TlOX precise information about the water content Chamber has two solvent compartments, one of their products. And so do those in the peat either end, each of 5.0 ml capacity. This troleum and plastics industries. The Mettler permits simultaneous development from either DL18 Karl Fischer Titrator is a cost-effective end of the TLC plate or sequential develop- tool to provide this information. ment. Further, mobile phases can be different in each solvent compartment or the same in Circle #52 on Readers' Inquiry Card both, greatly extending the number of samples Four precision laboratory balances, two of under development, when mobile phases are which are equipped with exclusive Mettter the same or allowing differing mobile phases DeltaRange are announced. These are desig- to be used in, e.g., optimization procedures. Controlled Heating/Cooling nated Mettler models PE380, PE600, PE360Q A feature of the Vega-T10X Chamber is the and PE6000. These units, plus models PE160 unit's versatility. It can accommodate one 10 and PE1600 introduced earlier, are designed X 10 cm TLC plate, up to two 5 X 10 cm to accept LabPac, Mettler pfug-in software. plates simuitaneouly or up to four 2.5 X 10 cm LabPac dedicates the balance to laboratory plate simultaneousiy. in operation the mobile routines such as net lotai weighing, percentage phase(s) is "wicked up" from either (or both) determinations, animal weighing, mean value of the solvent compartments to contact the (x), and standard deviation. Models PE360 and TLC plate sorbent. Capillary action ensures an PE3600 feature DeltaRange, a fine weighing even, constant mobile phase supply and, as range that can be recalled at the touch of a one result, separations exhibit excellent lin- button for weigh! determinations with a 10- earity. Vega-T10X TLC Developing Chambers times better resolution. This makes it possible are supplied with wicks (package of 25) and an to accurately weigh very light components into ACCUFLAT. Replacement wicks, cover heavy containers on one and the same bal- glasses and saturation sheets {used when ance. Model PE360 has a 0-360 g weighing saturated-chamber development is required) range and reads to 0.01 g. Its DeltaRange are ail readily available from Astec and from weighing range is 60 g, reading to 0.001 g. For selected laboratory supply dealers. the PE3600, the ranges are 0-3600 g and 600 FTS Ko-Cooi Controlled Rate Freezers provide g; the readabilities are 0.1 g and 0.01 g. Models a reliable and convenient means of obtaining PE600 and PE6000 have capacities of 610 g Circle #55 on Readers' inquiry Card precisely controlled cooling and heating rales and 6100 g, respectively with readabilities of for a variety of applications. Because the 0.01 and 0.1 g respectively. Compared to Sio-Cooi is mechanically refrigerated, no liquid previous models, the new PE balances show HPLC Contamination Protection nitrogen is required for operation—only a number of interesting technological inno- standard electrical current and a heat transfer vations. For example, a standby circuit makes Two types of guard columns to prevent fiqitid medium such as methanol. Temperature sure that the balance is ready to operate as chromatography samples with non-eluting Ranges to-45°C, -70°Cand -120°Care IContinued on page A1Q4)

Volume 61 Number 3 March 1984 A103 Impurities, and to permit autoolavlng and re- out of the use. Vial closures and seals are sold sepa- 1 rately to accommodate vial re-use. Vials are sold In quantities of 100 with discounts allowed editor) bo/ket on volume orders. Crimpers, decappers and other accessories are also available. All items . are sold from stock for prompt availability. materials trom contaminating HPtC coloms Prices, say the company, are tower than those have been Introduced by IBM Instruments, Inc. from other suppliers. The guard columns are compatible with HPLC instrumentation and cost less than standard arete #58 on Readers' Inquiry Card HPLC versions. The new columns are designed to prolong the life of analytical coiumns without degrading chromatography, reducing the cost Non-slick Valves per sample analyzed. Two types of guard columns are available, with norma! (silica) or reversed-phase (octadecyl) pellicutar packings. Each guard column kit contains 4.5 mm X 50 mm repaokable hardware and 6 g of packing material. Replacement packing is available in 10 g units. Circle #SS on Readers' Inquiry Card

3A Sanitary Metering Pump

of Blood Banks, The American Red Cross and The Federal Food and Drug Administration. A mobile single door unit (model BPL 13) has capacity for 284 of the standard 400 mi capacity packs, double-door units (BPL 21) with 462 pack capacity and four-door models (BPL 41) hofdlng 768 plasma packs all have temperature monitoring safety alarm systems featuring the built-in surveillance module guaranteeing safe storage. Module design includes: a constant LED digital display of interior temperature in tenths of degrees Celsius, a monitor light and audible signal Indicating safe operation, or warning alarm when temperature gets too high, door—ajar warning signal and FMIRP-SAN pumps conform to the 3A Sani- a battery operated power failure alarm, A tary Code of the U.S. Pubiic Health Service. seven-day temperature recording thermometer Designed for high accuracy and dependabiiity, Sew "non-stick" valve from is standard. Durable stainless steel Interior the pumps provide long trouble-free service 3SG Industries construction with removable drawers and four In food, dairy, drug, and pharmaceutical ap- inch Siick polyurethane vapor sealed insulation plications. Because of Its high reliability and MQ Scientific Gases, a division of MG Indus- Insures many years of energy-saving, trouble accuracy. Model RP-SAN is an excellent tool tries, announces a unique diaphragm valve for free operalion. Uniform cabinet temperatures for pumping expensive substances such as cylinders used for high purity, rare gases and of —35°C are maintained by a rapid recovery concentrated vitamins, flavors, odorants, gas mixtures. According to Rudi Endrea, fan circulation system. Jewett blood plasma colorants and other additives commonly used General Manager, "The newly designed valves storage freezers are equipped with safe au- in the dairy, food, and drug industries. The incorporate an easy-to-use, energy efficient tomatic defrost, condensate evaporators and pumps have only one moving part (the piston) handwheel that eliminates the traditional door fasteners with cylinder locks for secu- and do not rely on valves that can clog or problems of freezing and sticking. We have rity. stick—the piston does the vaivlng. The cost Incorporated CGA & DIN type threads for do- effectiveness realized from 1 % or better re- mestic as well as International applications. Circle #60 on Readers' Inquiry Card peat accuracy makes the RP-SAN an excellent Tests show that the valves have proven to be pump for critical metering needs. Standard extremely effective with reactive as well as units are available for flows to 1 liter per min- nonreactive gases. In our opinion, this will ute and pressures to 100 pslg. eliminate a big headache for many users." Strip and Platen Heater Features of the V6 diaphragm-type valve in- Circle #57 on Readers' Inquiry Cartf clude smooth operation, superior airtlghtness, • significantly lower gas losses, high gas tight- ness and a long service life. The soft-to-the- Autosampler Vials touch handwheel provides a positive grip and is resistent to thermal and mechanical stress. Phase Sep announces a complete selection MG valves are stocked and distributed from of borosilicafe glass vials for LC, GC, AA and over 50 locations throughout the U.S. other autosamplers. Original equipment Circle #59 on Readers' Inquiry Card equivalent replacements are available for all commercially available autosamplers, according to company. A variety of vial size and types are offered, compatible with original Blood Plasma Storage Freezers manufacturer specifications. Screw or crimp The Jewett Refrigerator Co., Inc. has intro- Watlow Eiectric Manufacturing Co. has intro- type closures are available with a broad range duced three models of blood plasma storage duced the Thincast Strip and Platen Heater, a of seal and septa materials to ensure com- freezers equipped with constant security and cast-In aluminum heater, designed to produce patibility with application and auto sampler surveillance system modules. Each meets or efficient, uniform heat up to 800 degrees F. type. Vials are made of borosilicate glass to exceeds the strict temperature standard re- The heater is just 1/2-in. thick, yet provides the prevent sample contamination from glass quirements set by The American Association exceptionally long life for which cast-In heaters

A104 Journal of Chemical Education are known. Ideal for extruder die heads, heat The manufacturer offers technical assistance sealing machines and heating and cooking on its toll free applications line. surfaces, Watlow's new Thincast Heater is Circle #64 on Readers' Inquiry Card available in widths of 1.5 to 6 in. and lengths from 8 to 22 In. It is available with welded stud terminals or flexible lead wires. Ceramic ter- Refrigerated Composite Sampler minal covers are available and standard lead length is 10 in. Circle #61 on Readers' Inquiry Card

Lauda Circulators

toring of any liquid or other environment requiring controlled temperatures. The units are equipped with rechargeable nicad batteries that are maintained at full capacity through a trickle charge system. These batteries take over in the event of power failuure to signal the problem and continuously survey tempera- American Sigma recently announced the in- tures. An included hermetically sealed relay troduction of the 6300 Refrigerated Composite aiiows simple connection to a master remote Sampler. The semi-permanent 6300 utiijzes station as an alternate mode of Installation, or a high speed peristaltic pump for sample col' the TPM may be paired with Hie TPMR remote lection. The %-in. ID intake lines are cleared monitor up to \ mile away. before and after every sample ... the post- Brinkmann Instruments Co., Division of Sybron Circle #63 on Readers' Inquiry Card sample purge is adjustable in duration from Corp., announces the line of Lauda constant 10-90 seconds. Liquid Is discharged under temperature circulators, including immersion, pressure to the 5 gallon polyethylene com- heating and refrigerating models, most with Rotary Mechanical Homogenlzer posite container. The sampler may be oper- digital temperature readout, Additional features ated on a timed-cycle basis or in proportion to includes a variable over-temperature safety the flow rate. The sample liquid Is held during shut-off which can be set to any temperture the collection period in a refrigerated com- within the operating range of trie circulator, partment maintaining a 4-1CC range. For independent of the set point temperature. If outdoor use, the 6300 is available with a overheating occurs, an aSarm sounds and weatherproof fiberglass enclosure which may power to the circulator is cut off. Several be optionally equipped with insulation and 500 models also feature protection against low watt heater. liquid level operation and duplex pumps for circulation to open external systems. Heater Circle #65 on Readers' Inquiry Cant wattage automatically adjusts to maintain the set temperature with an accuracy of up to ±0.01°C, regardless of load. Zero cross-over Mercury Collector swItching/HFI suppression eliminates the possibility of electrical interference with other sensitive laboratory instrumentation. Energy- efficient refrigerating models offer up to 75 % savings in power consumption compared to conventional cooling systems. A microprocessor-based programmer accessory is available for heating and refrigerating models.

Circle #82 on Readers' Inquiry Card Heat Systems-Ultrasonics announces a complete line of rotary mechanical homogenizers Temperature Monitoring Systems and accessories. The Astramixer units mix, The Jewett Refrigerator Co., Inc. has intro- emulsify, disperse arid homogenize by high duced a line of 15 Temperature Monitoring and intensity or mechanical and hydraulic shearing Chemtrix, Inc., announces a unique item that Temperature Power Monitor systems. Not only action. Included in the line are two laboratory no laboratory which is concerned about safety does the TPM system monitor temperature and size units. The micro mixer is available with should be without, the Mercury Collector. power failure condition, but in the event of three different rotor/stator sets; 7 mm, 12 mm When a mercury spill occurs, the foam-lined power toss, it continues to watch temperatures and 21 mm, allowing processing of samples lid is placed on top of the mercury and pressed while signaling the source of the problem. A from 250 microliters to 1 liter. The standard f irmiy. The special foam holds the droplets until steady or flashing red light along with preset faboratory unit is available with 35 mm and 45 the lid is screwed onto the plastic collector; audible alarm signals, Indicate varied alarm mm rotor/stator sets for processing 100 ml whereby, the mercury Is released to the bot- conditions with particular frequency pitches; through 20 liter batches. An In-line attachment tom of the collector for safe disposal. the factory set units insure accuracy within allows processing up to 5 gallons per minute Circle §66 on Readers' inquiry Card ±.2° centigrade. Designed for Blood Bank on a flow thru basis. Also available are industrial scale units capable of 6000 gallons on a Refrigerators and Plasma Freezers, the TPM (Continued on page A106) unit is easily adaptable for continuous moni- batch basis and 1785 gpm on a flow thru basis.

Volume 61 Number 3 March 1984 A10S thai are hard to clean by conventional meth- of the Isolab Ouik-Sep iuer-tipped polystyrene out of the ods. Made of stainless steel, the tanks of the column. Column volume is 6.S mL (total), with cleaners have capacities ranging from one pint 6.0 cm barrel height, interior diameter is 8.0 to two gallons with 40 walls to 200 watts of mm. The bottom of the column barret is flat, editor > bo/ket cleaning power. Larger models have bottom- not tapered, providing less opportunity for mounted drains and are available with mixing in the tip. Available empty, with plastic heaters/timers. filter disc (average pore size 50 jum), or glass OH McLeod Gage, Titling Type Circle #68 on Readers' Inquiry Card microtiber fitter disc (S8S no. 24). For use with aqueous systems only. Circle #71 on Headers' Inquiry Card Ultrasonic Homogenlzer/Cell Disrupter

Tissue Holder Ever reach for tissues Just to find that they're either out of reach or buried underneath something? Not any morel The handy Isolab Kimwlpe Holder, wall or cabinet mounted, provides ready access to the standard size 3 (5%-in. X 3-ln. X 4 /4-in.) Kimwipe box. Circle #72 on Readers' Inquiry Card

Liquid Dispensing The Micro-Pipex Is a light, hand-held instrument for conveniently dispensing liquids from glass capiiiary rnlcroplpets without using a mouth tube. Liquid is drawn into or dispensed from the pipet by rotating a thumbwheel. A fast-release button ailows suction by capillary action alone or quick delivery of pipet contents. The Isolab Micrc-^ipex gives smooth and B. Braun •r.strur'ients announces the Braurt- precise control over what has been a tedious Somc 2000, a high energy, ultrasonic ho- procedure. A mercury-free, oil MoLeod gage, tilting type mogenizer and cell disrupter. Consisting of a Circle #73 on Readers' Inquiry Card has been added to the Gilmont tine of labora- generator, transducer and a wide selection of tory instruments. The degassing design is probe tips, the main unit occupies 70 space- similar to the earlier patented design break- saving square In. of bench space. Modulation through of the oil swivel type. A high diffusion of the voltage waveform is a unique feature of pump oil takes the place of the conventional the instrument. The acoustic wave from the New Literature mercury and Its attendant toxicity. At the same probe tip is a function of the voltage waveform time, the sensitivity ol measurement Is im- energizing the four piezoelectric elements of Hazardous Waste Chart proved. Principal design features of the gage the transducer. The result is less generated are: Teflon valve on closed end simplifies heat and longer running periods. ... up to a filling and cleaning, Additional teflon valve continuous half hour. Isolates gage from system. Sensitivity range Circle #69 on Headers' Inquiry Card from 1 miHitorr to 2 torr, Accuracy: ±2% of reading or £1 mm of scale, whichever Is larger. Accuracy achieved with larger preci- Ultra Low Volume Cell sion bore capillaries and adjustment of bulb volume to ± 1 %, Buift-in rotary check vafve for personnel/gage safety. Corrosion resistant plastic for long life, High vacuum Viton O-rings for all seals, Requires only 10 ml of diffusion oli, and Cicumfereotial acryilc housing for gage protection.

Qrcte #67 on Readers' Inquiry Card

Ultrasonic Cleaners

Ultra low volume flow-thru capillary cells are now available from Harrick Scientific Corp. for liquid and gas chromatography studies. These cells have a gold-plated 3 mm bore and lengths of 5 or 10 cm, with volumes of 0.35 and 0.7 cc, respectively (other lengths can be specially made). Windows are removeable and sealed Anyone who collects, stores or transports to ttie tubulatlon via miniature O-rings. Con- chemical waste must determine if the waste struction Is such that there is no dead volume. is considered hazardous under the provision These light pipe celis can be used in most of the Resource Conservation and Recovery spectrophotometers with appropriate 4X Act, and if the waste Is considered hazardous, beam condensers. it must be identified with a RCRA number. This Chemtrix, Inc., Introduces a complete line of Circle #70 on Readers' inquiry Card Information can be found in the Federal Reg- industrial ultrasonic cleaners which can re- ister but only with difficulty. To make It easier move oil, tar, agar, food, rust, ink, blood, etc. to obtain this information. Lab Safety Supply from giassware, laboratory equipment, surgi- Plastic Column Co. has published a chart that makes this information more readily available. This 17-in. cal and dental instruments, electronic com- Valves, needles, etc. with iuer fittings wlft snap X 22-ln. chart aids in identifying the classes ponents, precision parts and many other items srtugfy In place on the specially designed tip

A106 Journal of Chemical Education of chemicals that are considered hazardous, supporting data of the 400 most commonly and provides the actual hazardous waste used solvents. It is the most comprehensive number for over 650 chemicals. This chart book available on organic solvents and serves helps in the identification of hazardous wastes as a convenient and practical desk reference and speeds op paperwork procedures requited which Is invaluable to chemists in solvent under RCRA. Identif ication and analysis. Information for each Circle #74 on Readers' Inquiry Card solvent is arranged on two pages in a large, easy-to-read format with the Infrared spectrum Macro lo Micro appearing on the page directly opposite the Split-Beam Spectrophotometer supporting chemical data. The spectra are h HPLC Columns presented in a transmittance vs. wavenumber format over the spectral region 4000 to 400 H 1 cm" , and all are clearly labeled with the i-f Featuring: source of sample and the sample preparation m Custom Phases technique used. Ail spectra are prepared in Sadtler's own laboratories, under the direction of Sadtfer's spectroscopists, using standard preparation and evaluation techniques which insure that these reference spectra are of the best possible quality. Each compound Is listed by its Chemical Abstracts name or its most readily recognizable name, together with frequently used synonyms. In addition, the CAS Registry Number and the NIOSH Number are given when available. Also, Hie data page provides the molecular formula and literature shape, and pore diameter and to define and values of physical properties such as melting select by structure the desired stationary point, boiling point, flash point, density and phase. The fi Chromega Microbore HPL Col- refractive Index. Additional information re- umns are available in most Chromegabond garding use, solubility, f tammability and toxiclty packings and come In standard lengths of 30 appears for most compounds, and nearly ail cm, 50 cm, and 1 meter. of the solvents are depicted by a conventional Circle #76 on Readers' Inquiry Card drawn structure and by the Wlswesser Line Notation. The compounds in The Infrared A full-cofor 8-page brochure detailing the Spectra Handbook of Common Organic Sol- HPLC Siomedlcal Applications Spectronlc 1001 split-beam spectrophoiom- vents are indexed both alphabetically and by An exciting set of applications is available from eter is available from Bausch & Lomb. in the molecular formula, allowing for the rapid lo- KBL Instruments, Inc., describing their line of split-beam optical system of the 1001, a small cation of any spectrum. In addition, the sol- Ion Exchange and Gel Filtration Columns. fraction of the abundant energy is split off and vents in the Handbook are classified Into four Chromatograms are optimized for high reso- used as a reference beam to give the instru- main groups; hydrocarbons, compounds hav- lution, rapid analysis, linearity, and selectivity. ment a level of stability previously associated ing only one type of characteristic atom or Compounds separated are proteins, peptides, only with double-beam spectrophotometers. functional group, compounds having more than and amlno acids on a preparative and analyt- High energy thai begins with high-intensity one type of characteristic atom or functional ical scale. The instrumentation required to source (amps is conveyed to each sample wiln group and deuterated compounds. optimize results is discussed and ranges from minimum loss by way of silica-coated toroidal state-of-the-art pulse-fee solvent delivery mirrors and a Bausch & Lomb holographic Circle #76 on Readers' Inquiry Card systems to LKB's "intelligent fraction collector. grating. As a result, the 1001 provides stable Complete systems can be operated automat- readings throughout the wide 190-950 nm ically using the HPLC controller and new au- wavelength range, and accurate measurement Ioin|ector. of samples from near 0A to beyond 3A with no Scientific Spectroscopy dilution. A high-resolution 2 nm spectral The Harrick Scientific Catalog of 1R-VIS-UV Circle #79 on Readers' Inquiry Card bandwidth and low stray radiant energy con- Accessories presents a complete line of tribute accuracy and fine-structure definition. spectroscoplc products. Crystals, polarizers, The brochure discusses typical communica- solid/liquid-gas sampling and other transmis- Gas Chromatographs tions with the 1001 with graphic iilustrations. sion accessories, specular external and in- A 16-page four-color brochure describes The user-friendly, duai function membrane ternal reflection as wed as diffuse reflection Varian's Vista 6000/6500 Gas Chromato- keyboard allows alphanumeric entries to be attachments, vacuum chambers, beam con- graphs. Key features of both the 6000, with its made easily. The "keys" have been carefully densers, and skin analyzers, for both disper- powerful built-in microcomputers, and the organized so that any user will be commanding sive and Fourier Transform UV-vislble and dual-column 6500 Satellite Chromatograph are the instrument comfortably and confidently infrared spectrophotometers. Other products covered in photographs and Illustrations that within a short period of time. The 1001 can be include plasma cleaners, pyrolysis chambers, complement the informative text. Expansion preprogrammed for various test types and spectrometer systems and much more. Many capabilities, modular construction, unique CRT operations. The internal RS-232-C computer products are new and listed for the first time. and keyboard features, and convenience- interface accessory further expands the Harrick Scientific also specializes In custom designed, large column oven, separate pneu- capabilities of the 1001 by permitting two-way instrumentation—designs to fit any spec- matics compartment and universal injector and communication between the instrument and trometer and meet all custom needs. detector bases are described in detail. Six virtually any computer. This brochure on the Circle #77 on Readers' Inquiry Card detector choices, a versatile injector system, Spectronic 1001 spectrophotometer provides and advanced capillary systems also are de- technical data; discusses product features and lineated, as is the optional 18080 AutoSampter routine test procedures; describes the indi- that provides total automation. vidual keyboard functions; lists custom sam- HPLC pling accessories, test types, and operations; A HPLC Brochure featuring mlcrobore tech- Circle #80 on Readers' Inquiry Card and provides samples of the display prompts nology and custom synthesized HPLC phases for a specific test program format. and packings is available from ES Industries. Included in this latest company literature is a Refractometers complete line of Chromega HPLC Columns, Circle #75 on Headers' Inquiry Card Sixteen-page, fully Illustrated catalog of Packings and Accessories for a wide range of complete line of refractometers, including preparative, analytical, and micro analytical hand-held, Abbe, and digital Instruments, Is Common Organic Solvents !R applications. In addition, the brochure intro- announced by NSG Precision Cells, Inc. The The Infrared Spectra Handbook of Common duced a line of Microbore HPLC Columns and Organic Solvents is a compilation of the in- a service for custom packings. This new ser- {Continued on page A108) frared spectra, physical constants and other vice makes It possible to specify particle size,

Volume 61 Number 3 March 1984 A107 technical manuals, and other reference and Wafer Analysis out of the training materials. Thomas Scientific announces their 1984/85 Circle #83 on Readers' Inquiry Cant Water Analysis Catalog. The catalog contains editorjr bo/ket 248 pages and Is the most comprehensive water testing catalog available. It is arranged Recorder alprianumerically for easy reference, and A four-coior brochure from Houston instrument contains over 2,500 items and over 600 pho- describes the extensive built-in intelligence, tographs and illustrations. Featured In the touch-panel controls and dependable me- catalog are LaMotte water testing kits, instru- refractometers are used for measuring the chanical features of the 4500 Microseribe. ments, and associated apparatus, individual sugar content of all types of food products. Photos and accurate descriptions define Hie test kits, multlparameter kits, portable meters, Also included are a series of clinical refrac- features which give the 4500 Microscribe and reagent systems are offered for more than tometers for determining serum protein and enhanced capability at a lower cost than a 60 chemical parameters. The catalog also urine specific gravity. Separate tables list the basic strip-chart recorder. Microprocessor contains a listing of virtually any piece of lab- Brlx and refractive Index and provide a guide control joins Hi's patented capacitance servo oratory apparatus or reagent, representing for selecting the correct instrument. rebafance system to assure flexibility and re- over 135 different manufacturers, needed in Circle #81 on Readers' Inquiry Card liability unprecedented In strip-chart recorders. the water/wastewater testing field. As a new In addition, an automatic self test function and feature, all prices in this catalog will be held dayiight-readabie liquid crystal display (LCD) firm by Thomas Scientific until January 1, IR/FTtR Accessories continuously Inform the operator of recorder 1985. parameters and status. The brochure contains thorough performance specifications, as well Circle #86 on Readers' Inquiry Card Extending as details o! genera! features and accessories. Viscometers and Rheometers Circle #B4 on Readers' Inquiry Card Capabilities Calibration Devices for Instrumentation Tracer Atlas, Inc., specialists in H;S measurement and instrumentation, has recently compiled and published a catalog revealing their line of calibration equipment. This catalog offers an overview of the devices including principles of operation and typical applications for each instrument. Technical fiefd services offered by the company are also mentioned. This easy to read, informative catalog pictures each device clearly. The products In the catalog include: kits for liquid and gas sample preparation; a pocket size generator for HES sampies; a standard reference gas generator; a gas calibration cylinder; and a linear motion Barnes Analyticai/Spectra-Tech has published syringe-drive for injecting gas, liquid or solid a 16-page 1984 Catalog titled Extending IfV sampies. A Spanish edition is aiso avail- FTIR Capabilities. The Catalog, which de- able. scribes more than 1,000 IFt and FTiR ac- A 24-page, fuff-color catalog details the Fann cessories, is reported to be one of the most Circle #85 on Readers' Inquiry Card Instruments product line of viscometers, comprehensive laboratory purchasing guides consistometers and related rheological In- of its kind ever produced. For the sake of strumentation for industrial, commercial, sci- troubie-fee reference, the Catalog Is divided Ultramlcrobaiance entific and academic applications, tn addition into eight main sections, according to Spec- A six-page brochure from Perkin-Elmer de- to direct-indicating viscometers, recording and tra-Tech, The sections are internal Reflec- scribes the ultramicrobalance, the AD-6 Au- high-temperature rheometers, consistometers tance; External Reflectance; Micro Sampling; tobalance, highlighting instrument features and and accessories, the new Fann catalog in- Temperature/Pyrolysis; Solid Sampling; Liquid benefits that simplify micro-weighing tasks cludes frequently needed viscosity computa- Sampling; Gas Sampling; & Crystals & Prisms. now more than ever before. The AD-6 offers tions and conversion factors. Information in the Spectra-Tech Catalog in- 0.1 microgram sensitivity with 5 gram ca- cludes guidelines on accessory use, prices and pacity, and nonvolatile memory for up to 899 Circle #89 on Readers' Inquiry Card other facts "designed to make selection as sampies. All operations are microprocessor easy as possible," the company stated. Spe- controlled through simple keyboard com- cial pages feature detailed reports on two of mands, which means weights can be stored, Minimize Gas Stream Contaminants Spectra-Tech's newest developments: the recalled, factored and statistically analyzed Scott's comparative study determines that CIRCLE for FTIR work with aqueous solutions; faster and easier. regulators with stainless steel diaphragms and the Collector for research with DRIFTS Circle #86 on Readers' Inquiry Cam minimize gas stream contaminants. Laboratory (Diffuse Reflection Infrared Fourier Transform Report E-R83-1 gives details of the study Spectroscopy). where three two-stage regulators were tested, Laboratory Water Systems including Scott's Model 18 high purity regu- Circle §82 on Readers' Inquiry Card A catalog on laboratory water purification lator. systems Is available from Millipore/Continentai Circle #90 on Readers' Inquiry Card Water Systems. The catalog (CG150) includes AA Spectrophotometers Accessories a review of current standards for laboratory Varian Associates' complete line of ac- reagent grade water, as well as descriptions cessories and supplies for its atomic absorp- of the company's complete line of products Miscellany tion spectrophotometers is deiineated in an and services for the laboratory. Included are 18-page color catalog. Photographs and de- water systems specifically designed for ap- scriptions of the AA support materials are plications requiring organic-free (less than 50 Six Millionth Substance in CA accompanied by ordering information, and ppb) water for such applications as critical Chemical Abstracts Service has recorded the listings on replacement parts, and spare board HPLC, and ultrapure, pyrogen-free water for six millionth chemical substance In the files of kits and cables, information aiso is included on use in sensitive biological areas. its Chemical Registry System. The total In- available audio-visuai training programs, Circle #87 on Readers' Inquiry Card ciudes al! unique chemical substances Indexed

A108 Journal of Chemical Education in Chemical Abstracts since January 1965, These Include: peak detection algorithms in the when the Registry began operating as an ad- software for negative peaks; changing the junct to Indexing operations at CAS. The six baseline treatments; and altering bunching millionth substance to be registered, 2-cy- factors within a specific run. ciohexyl-3-methyl-4-(pentylamino)-E!-cyclo- A routine customized for ion chromatogra- penten-1-one, was disclosed in a West Ger- phy allows the operator to designate the man patent application filed by Masayoshi baseline so that negative excursions In the Mlnai and Tadashi Katsura of Sumitomo chromatogram—typical in ion chromatogra- Chemical Company, Ltd., of Japan. It was one phy—do not affect the baseline and peak- of 360,000 new substances added to the detection treatments. Quantltatlons by internal Registry file in the past year. The patent ap- or external standards are possible, and final plication also describes 66 other cyclopen- results displaying area percent reports, re- tenone derivatives synthesized by the inven- plotted chromatograms with baselines and tors. Including reactants involved in the syn- peak names are included in the software. A!) theses, CAS Indexed 137 substances from the raw data is stored on disk for easy recall of patent document. stored runs, or alteration of baselines for new calculations, in addition, the chromatograms CAS developed the Chemical Registry can be recalculated with different Integration System in the early 1960'a to provide a means parameters and calibration curves. Special for determining whether a chemical substance routines in the software allow the user to recall reported in the scientific literature had been and graphically compare stored ion chro- indexed previously In Chemical Abstracts and matograms, subtract chromatograms and retrieving ihe previously assigned index name perform ratio calculations. The rOelson Ana- if i! had. The system now performs about 6000 lytical Model 4416 data system includes substance identifications each working day in hardware, A/D interface, and software for ion support of Indexing operations at CAS. The chromatography. Registry also is the basis for the CAS ONLINE search service, which makes It possible to Circle #93 on Readers' Inquiry Card search the file of 6 million substances by name or structural characteristics to retrieve structure diagrams, names and bibliographic cita- tions for substances of interest. General Chemistry Software A software program for high school, college University Microfilms Circle #91 on Headers' Inquiry Card and university students named "Introduction to General Chemistry" has been given a 1983 International Learning Computer Software award. The Software Programs COMPress program is designed as a supple- UV Software Notes, written by Perkin-Elmer ment to an introductory course in General Chemistry for students with no previous personnel and users of Perkin-Elmer instru- Please send additional information ments, computers, and software are available. Chemistry background. By simulating Chem- The typical UV Software Note describes a istry experiments on the computer, students specific application, usually quite small and not are exposed to realistic laboratory situations fray- Journal O! Chsmica] Education covered by Perkln-Eimer price listed software, whldi saves time and the cost of actual ex- and includes simple instructions on how to run periments. Additionally, the program allows the program. Programs are formatted for the students to gain experience in collecting and Perkin-Elmer model 3600 Data Station and are interpreting data. Extensive use of color ani- written in either the BASIC or OBEY language mations tn an interactive format keeps student of the Perkin-Eimer Computerized UV (PECUV) interest high. "Introduction to General Chem- application software. Current programs in- istry" is presently a seven-disk series. "We clude: 1) A program for Hard Copy Printout on plan to add six disks to the series in 1984," the PR-100 Printer, 2) A program to Labei a said Thomas L. Sears, General Manager of Spectrum, 3) Wavelength Programming for COMPress. "We are proud of the industry Lambda 3, 4) User Programming with Lambda recognition for this program and the program 5, and 5) First Order Kinetics. authors, Professor Stanley Smith, University of Illinois, Dr. Ruth Chabay, and Dr. Elizabeth Circle #92 on Readers' Inquiry Card Kean." All entries for Learning Computer Software Awards are judged by a committee of teachers, subject specialists, computer State- Ion Chromatography Software educators and instructional media devel- opers. A dedicated software package developed for Zip. Ion chromatography applications has been introduced by Kelson Analytical. Inc. This Circle #94 on Readers' Inquiry Card software is offered as part of the standard chromatography software package for Nelson Analytical^ 4400 series multi-instrument data Educational Computer Labs 300 North Zeeb Street systems, which are based on the HP 200 se- Fisher Scientific Company, Educational Ma- Dept. P.R. ries desktop computers. Data from up to 10 ion terials Division, located In Chicago, Illinois, has chromatographs (20 detectors), or conven- installed fifty-two Commodore 64 Computer Ann Arbor, Mi. 48106 tional gas and liquid chromatographs can be Laboratories in selected elementary, junior U.S.A. processed on the same system simulta- high, and senior high schools in the District of neously. Each ion chromatograph is connected Columbia Public Schools. These laboratories to the Model 4416 data system through a will be used for teacher training and computer 30-32 Mortimer Street Neison Analytical intelligent Interlace—a literacy instruction for students. Thirteen !abs Dept. P.R. 20-bit precision analog-to-digita! converter. were in use this summar for a Summer Com- This interface collects the analog signal from puter Camp Program. Each laboratory consists London WIN 7RA the chromatograph and stores it in digitized of ten Commodore 64 computers and monitors England form. Data sampling rates for this system which are networked to a common disk drive range from one point per 10 seconds to 100 via the MUPET networking system that allows points per second. With the chromatography students to share a common disk drive and software installed, the Mode! 4416 system lets printer. AM computers are individually housed the operator construct ion chromatography and secured to computer furniture. methods for the specific application required. Circle #95 on Readers' Inquiry Card

Volume 61 Number 3 March 1984 A109 Publications of the DIVISION OF CHEMICAL EDUCATION, A.C.S. SAFETY IN THE CHEMICAL LABORATORY TESTED DEMONSTRATIONS IN CHEMISTRY Vol. 1—Edited by N. V. Steere This 6th edition contains all the "Tested Demonstrations in General Chemistry"by H. N.Alyea, which appeared in J.Chem. Ed. in 1955 This paperback report contains alS of the contributions to the monthly and 1956; "Demonstration Abstracts" compiled by Professor Alyea feature, "Safety in the Chemical Laboratory" which have appeared from all the demonstrations which appeared in J, Chem. Ed. from in J. Chem. Ed. from January 1964 through January 1967. Paperback, 1924 through 1959; 168 "Chem. Ed. Tested Demonstrations" edited 132 pp., US $10.35, Foreign $11.25- (Postpaid) by F. B, Dutton, and a complete index of all the contents. Paperback, 236 pp., US $10.35, Foreign $11.25. (Postpaid) Vol. 2—Edited by N. V. Steere Contains ail of the articles from the "Safety in the Chemical Labo- ratory" column which have appeared from February 1967 through TOPS IN GENERAL CHEMISTRY—3rd Ed. January 1970.1971 Paperback, 132 pp., US $10.35, Foreign $11.25. (Postpaid) (Tested Overhead Projection Series)—H. N. Alyea Vol. 3—Edited by N. V. Steere This reprint contains all the installments published in the J. Chem. Ed. from January 1962 through June 1967. Included are articles on Contains at! of the articles from the "Safety in the Chemical Labo- the construction of inexpensive overhead projectors and the basic kit ratory" column which have appeared from February 1970 through of simplified TOPS devices. Paperback, 144 pp., US $8.35, Foreign January 1974.1974 Paperback, 157 pp., US $10.35, Foreign $11.25. $9.25. (Postpaid) (Postpaid)

Vol. 4—Edited by M. M. Renfrew CHEMISTRY OF ART (Offprint) Contains all articles from the "Safety in the Chemical Laboratory" column from January 1974 to January 1980, and, in addition, all other A series_ of articles published in the 1980 April issue of the J. Chem. relevant material on safety published in the J, Chem, Ed. during ihe Ed. designed to increase teachers' knowledge of the chemistry of art. same period including special articles, notes, letters, and book reviews. The papers include the topics color, light, ceramics, safety and metal The papers have been grouped by subject area and an extensive index artifacts. Paperback, 28 pp., US $3.50, Foreign $3.90. (Postpaid) prepared. Updated material provided by original authors. 1981 Pa- perback, 150 pp., US $11.60, Foreign $12.50. (Postpaid) CHEMISTRY OF ART—A SEQUEL (Offprint) ITERATIONS: Computing in the Journal of Contains twelve articles which appeared in the April 1981 issue of the J. Chem. Ed. In general, these articles contain more descriptive Chemical Education—Edited by J. W. Moore chemistry and are more technologically oriented than Chemistry of The first 16 articles from the Computer Series together with a dozen Art described above and will function well as a complementary set more full-length descriptions of computer applications from the 1979 of teaching materials. 1981 Paperback, 44 pp., US $5.00, Foreign $5.40. through April 1981 issues of J. Chem, Ed. are contained in this vol- (Postpaid) ume. It covers all aspects of computer and calculator applications in classrooms and laboratory from introductory to advanced level. There is a wide variety of short descriptions of specific computer programs, STATE OF THE ART SYMPOSIA OFFPRINTS and a bibliography that lists all computer-related articles that have appeared from 1959 through 1980. 1981 Paperback, 144 pp., US Since 1980 the Division of Chemical Education has been presenting $11,60, Foreign $12.50. (Postpaid) a series of symposia at ACS national meetings on selected rapidly developing areas of chemistry. The symposia are designed to bring critical information and ideas to a state where it may be used by J. CHEM. ED. CUMULATIVE INDEXES teachers immediately. All symposia have a strong pedagogical emphasis with an introductory focus on background material so that a Vols. 1-25 (1925-1949) 25-ye»r US $9.50, For. $9.90 teacher familiar with mainstream chemistry will be able to understand Vola.2&-35 (1949-1958) 10-year USS9.50,For.$9.90 and use the information presented. Later papers build on the foun- Vols. 36-45 (1958-1968) 10-year US $9.50, For. (9.90 dations laid in the firstpapers . The published proceedings in J. Chem. Ed. of these State of the Art Symposia are available as offprints. Classroom quantities (10 or HANDBOOK FOR TEACHING ASSISTANTS more of each offprint) may be purchased at-a 20% discount from the This pocket-steed booklet is designed for new teaching assistants. It single copy price. gives information on various aspects of the assistant's work, including how to conduct a recitation class, how to conduct a laboratory, how to grade, how i» prepare for recitations and laboratories. 1983 Pa- SOLID STATE CHEMISTRY perback, lots of 10 copies only, US $12.60, Foreign $13.50. (Post- paid) 1980 Paperback, 61 pp., US $5.50, Foreign 55.90. (Postpaid)

COLLECTED READINGS IN INORGANIC RADIATION CHEMISTRY CHEMISTRY VOL. 2—Edited by G. Galloway 1981 Paperback, 96 pp., US $6.50, Foreign $6.90. (Postpaid) This newest reprint collection contains papers selected from among those which have appeared in the J- Chem. Ed, between 1962 ana 1971. Topics included are bonding, periodicity, chemical dynamics, POLYMER CHEMISTRY energy relationships, descriptive and practical, physical and inorganic chemistry, atomic and molecular. Paperback, US $9.10, Foreign 1981 Paperback, 120 pp., US $7.50, Foreign $7.90. (Postpaid) $10.00. (Postpaid) LASERS FROM THE GROUND UP MODERN EXPERIMENTS FOR INTRODUCTORY 1982 Paperback, 6* pp., US $5.50, Foreign $5.90. (Postpaid) COLLEGE CHEMISTRY—Complied by H. A. Neidig, W. F. Keiffer COUNTING MOLECULES—Approaching the Seventy-one articles from the J. Chem. Ed. have been reprinted in Limits of Chemical Analysis this one volume. These experiments were selected because they reflect the exciting changes that are possible in the laboratory work in in- 1983 Paperback, 48 pp., US $5.00, Foreign $5.40. (Postpaid) troductory, college chemistry. The articles are written for professors to use, not as prestyied specific directions, but to be adopted and adapted to their own courses. Paperback, 150 pp., US $8.35, Foreign ELECTROCHEMISTRY $9.25. (Postpaid) 1983 Paperback, 84 pp., US $6.50, Foreign $6.90. (Postpaid) SEND PREPAID ORDERS TO SUBSCRIPTION AND BOOK ORDER DEPT. JOURNAL OF CHEMICAL EDUCATION 20th & NORTHAMPTON STREETS, EASTON, PENNSYLVANIA 18042 ACS

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The Subjective Nature of Science The importance of science as a componentargue ni d the tha existenct sciencee is subjective because its progress is driven Therof mose ist, contemporar however,y considerabl societiese canno disagreement bet seriousl amontobyyg develo choice debatedhighlpy. a .Scientists welsl a chooss thee th methode areass by of whic knowledgh thaet the knowledgy wishe will questionrespecteds thaindividualt arises whewhon thhavee demand thoughst o fdeepl scientifiyabe c abousubset— sought objectivitt tha.ey Thus possibl,y ni mino ther fina one—ol analysisf the, scienc humaen ca conditionn be. seen as traineclashd wit scientistsh the, objectivit obligatioyn become to pursus aes societanatural agoalstoolAlthougss breathing. ho Fof rmanlogi, cwelly -withi scientistn sthe hav contexe acquiret ofd thei somre profession very, powerfu theyl are ratheyetr the explici charactet questionr ofs man ofy ethic societas tol issues less, well-define whicthnohetd rangenecessarilysubjectiv quesse- from aspects of perceived probiemwell-equippesd tha tby face thei rso- training to deal with solutioerationtionsns tha band/oty appea thosr politicser U traine),d generallhav easy thei scientists doer ssolution. no Ats see mni cleaciety reconomiTh amenabl -codee consummatce o fconsid to behavio-e rscientist will refuse to move beyond his/ sciencehas evolve. Thde ove ethors the of ias scienct wfee involve centuriess th toe acceptancguidmaturitinformatiohere ytechnica thene of o thaproceslr th etcompetenc re is-s science oeithefe.r wheYet unavailabln, thes faceed aro witreh exceed the question svery thse situation requirin levelgs o fwhen jectioentifiimpersonacn finding ofl criteriathse so reporte, athasdt wel thefindingyl as are thofe availabl other publisec oton presentatiojudgmentth th pre-establisheee publi nentir.c eo Thusfd turnscien sci-,s- eve ton science—rightl when ay scientist' or swrongly—fo trainingr dictate informesd that aftetificr communitycritical revie.w The by latte thosr eis knowledgeablusually, aned nipreferablythprecisionae th scientificalle limit, field—s donthay otef- sam acceptabluncertainte traininey commen gof shoulanytd responsecanno productse be and/oan mad rappraisae the witl inferh of- involverefereess, symposiu organizemd skepticis chairmenm, tha andt subject editorss. reporte Ad enceparTh findingtse of drawn strainin theg. etho ofs scientists is not totally devoid of skills that levelScientisttos continuin sof ar uncertaintge criticaexpecteyld ni revie tow thei poinr wit findinght ou nsot anth deassuranc limitationni amighe th e sensotsf ewelinference finalityand/o lof brs.e responsibilit usefuly ni is addressin amongg societa the lhighl issuesy .desirabl Fore example traits, debtednesthey draws .to The othery sare whos alsoe expectework—whethed tor acknowledg publishetoessencthat gede earte o ottheif rhone scientifir thde in-c tbottoom responsibilit a fin oefy things edg derivee. ni Scientists fromthes trainin a tenndg inne to orf persis neescientistsdt unti. Thle tributioSciencunpublished—haen isbuild, thuss upo,contribute an communa thde wortokl thei enterpris ofr othersaccomplishmentse ni. whicFurthermoretheyh. understan every, d scientistcon th-es tru aree natursupposeed of to the be proble mable befortoe expres thems. These characteristics of science are the basisadmithei fort threservation errore widel. That'sy fullsy no antd a honestly bad lis,t an dof traittos be tob eprepare ablde toto bring helbed mad opinioen for tha at "sciencfundamentae ils subjectivit objectivey" ni yet science ato poin. bea Somtr als eoon hav casocietane l problems. JJL

Volume 61 Number 3 Marc18h3 1984 In thf/ Ixrue

G. N, Lewis Symposium Even the direct use of solar energy in the form of heat energy has its technical problems, particularly in those areas The last four papers of the proceedings of the G. N. Lewis where fairly large amounts of heat energy have to be stored Symposium appear in this issue. The papers by Stranges to compensate for the unpredictabilty of the energy source, (page 185J, Jensen (page 191), and Pauling (page 201) each Spears and Spears (page 252) recycle an old favorite, the treat a different aspect of the development and acceptance demonstration which uses C0CI2 to illustrate the facile change of the Lewis theory of bonding, The fourth paper, by Kasha in coordination number by some transition metals, and use (page 204), relates the details of Lewis' last major investigative its endothermie reaction as a heat storage device in an ex- work—research with Kasha to confirm their ideas on the periment that can be performed at the advanced high school triplet states of molecules. or first-year college level. All of the papers in the G. N. Lewis Symposium in the last three issues have been designated by a drawing of Lewis that is adapted from an original that appeared in CHEMTECH. We wish to thank the artist, Alan Kahan, and CHEMTECH Organic Chemistry for ailowing us to use this drawing as our Symposium logo. Organic chemistry covers such a wide range of compounds and, by extension, theoretical and experimental approaches Solar Energy that it is one of the key building blocks of the undergraduate Solar energy has captured the imagination of a large aeg- curriculum. It appears in many guises, from theoretical ment of the population which is interested in alternatives to treatments involving thermodynamics to practical applica- fossil fuel resources. The existence of a "free" source of energy tions of natural products that are intimate parts of our daily is very seductive, particularly to those who perceive oar cur- lives. Several articles in this issue are about one of these many rent energy sources as either an environmental or economic aspects of organic chemistry. threat. The heat generated by these latter perceptions con- Before it is decided whether a particular reaction or theory stitutes a secondary energy source in itself; however, the is appropriate for the organic course, it is necessary to examine teacher of chemistry can exploit this intense interest to shed what the objectives of the organic course as a whole should be. some light on difficult concepts involving semiconductors and In this month's Goals feature (page 239), two authors, Clapp thermodynamics as well as on the limits of science to solve and Johnson, from a university and a high school, respec- social problems. Three articles in this issue focus on one of the tively, give their views on the values as well as the contents of technical aspects of solar energy utilization and include dis- the organic course at each of their institutions. cussion of practical applications and limitations. The recognition of the bond resonance, in benzene is the very There are two modes of solar energy use which are of current heart of much of the bonding theory of organic chemistry. interest: the direct storage and use of heat energy from in- George, Bock, and Trachtman (page 225) evaluate the frared solar radiation and the conversion of light to electrical empirically derived resonance energies as thermodynamic or chemical energy. McDevitt (page 217) in his article reaction energies. Another application of resonance theory has "Photoeiectrochemical Solar Cells" explores the latter mode, been in explaining the anti-Markovnikov addition, In this explaining the role of semiconductors in effecting the energy month's Textbook Forum, Tedder (page 237) points out that conversion and the problems involved in finding processes the explanations of free radical addition to alkenes given in which efficiently utilize the solar spectrum. He also gives di- most texts are often misleading and sometimes wrong, partly rections for preparing a workable photoelectrochemical cell due to the reluctance of authors to develop the more compli- which demonstrates many of the principles involved in this cated, but accurate, picture. complex problem. Teachers looking for some interesting history as well as Adamson, Namnath, Shastry. and Slaw son (page 221) some practical applications of organic chemistry will find take a more basic approach to solar energy by deriving the Cummings' Profiles in Chemistry on Wallace Hume Car- theoretical limitations to the efficiency with which light energy others both informative and useful. Another article with a can be converted to work. They show how application of "real world" biochemistry application is this month's Einstein's law of photochemical equivalence places a limita- Thumbnail Sketches feature in which Fernelius answers the tion on how much of the available spectrum can be used for question: "Is Sugar from Sugar Beets the Same as Sugar from a particular conversion process and how the application of the Sugar Cane?" laws of thermodynamics produces yet another limit on the An experiment which teachesth e theory and application conversion's theoretical efficiency. They conclude that solar of HPLC by expanding the traditional organic exercise on the energy is more efficiently utilized when it is absorbed directly separation of a carotenoid from the chlorophylls of a vegetable for heating purposes. Their approach, which includes chemical is provided by Silveira, Koehlor, Beadel, and Monroe (page examples, would make a useful classroom presentation since 264). Another aspect of the organic laboratory, the dangers it points out clearly that not all of that "free" energy is just involved in unsuspected peroxide formation is aging solvents, laying around waiting to be turned into electricity as some in is discussed by Nagel (page 250} in this month's Safety Tips the popular press would have us believe. feature.

184 Journal of Chemical Education Reflections on the Electron Theory of the Chemical Bond: 1900-1925

Anthony N. Stranges Department of History, Texas A&M University, College Station, TX 77843

Science has so deeply influenced our lives that we some- ories that supported an electrical attraction between atoms times tend to see scientific ideas as something final, something dominated the physical sciences. But near the middle of the eternal and static. In reality, scientific ideas are human cre- century these theories began to dimmish in popularity among ations with their own history, and their historical study often chemists. The reasons for their fall are several, but the one of contributes to a more complete understanding of modern most importance was the rise of organic chemistry. Chemists science. The electron theory of the chemical bond is one of the increasingly studied substances of vegetable and animal origin many important ideas that became a part of modern science. and were content only to analyze the number, kind, and ar- This essay will examine its history (1). rangement of the atoms, usually carbon, hydrogen, and oxy- The first electrical theories of the chemical bond accounted gen, in those substances. They paid no attention to the force successfully for the large number of inorganic compounds that holding these atoms together. chemists and physicists knew were clearly electrical in be- The rapid rise of the chemical industry, particularly in havior. When applied to the much larger number of organic Germany in the second half of the 19th century, made evident compounds, they proved inadequate. The bond in organic organic chemistry's newly acquired prominence. German compounds did not receive a successful interpretation until chemists carried out analyses and syntheses of dyes, drugs, 1916 when G. N. Lewis (1875-1946) at the University of Cal- and petrochemicals, all organic substances, without assuming ifornia, Berkeley, announced his theory of the shared electron any electrical theory of attraction. A simple line represented pair. Lewis showed further that the formation of electrical the bond uniting atoms in these compounds. The British compounds was only a special case of hia more general theory. chemist, William Tilden (1842-1926), pointed out this 19th His theory remains to this day the foundation of modern century development much later in a lecture before the Lon- chemical bond theory. don Chemical Society (5)

Nineteenth Century Ideas on Electrical Combination We have a universally acknowledged system of combination ex- Quite early in the 19th century, natural philosophers, the hibited by atoms without necessarily forming any hypothesis on chemists and physicists of that time, had agreed that all the nature of their attractive force. bodies—solid, liquid, and gaseous—consisted of atoms. They Organic chemistry had diverted the attention of chemists cailed a body that contained atoms of one kind, an element; from any theoretical explanation of the bond between atoms. a body composed of two or more different kinds of atoms was The excitement of discovering new compounds was, appar- a compound. Natural philosophers also recognized at this time ently, sufficient justification for not considering such a spec- that an electrical force held the atoms together. Construction ulative problem. At the same time, organic chemists revealed of the first electrical battery and the discovery of the electric the fundamental weakness of the electrical theory of attrac- current by the Italian Alessandro Volta (1745-1827} in 1800 tion. They showed that in organic compounds, the most established that a chemical reaction between different kinds prevalent bond was the bond between two carbon atoms. But of atoms produced an electric current (2). A demonstration carbon atoms were all alike, and, therefore, they should not of the opposite effect followed almost immediately. William have the opposite charges required to attract and bind one to Nicholson (1753-1815) and Anthony Carlisle (1768-1840) in another. London showed that an electric current could separate a The physicists, unlike most chemists, never abandoned compound into its atoms. They found that the compound, their belief in the electrical properties of atoms. But their water, consisted of two gases: hydrogen and oxygen (3). After investigations centered mainly on the atom's kinetics, the other investigators, chiefly Humphry Davy (1778-1829) at the fields of force around an atom, and the question of whether Royal Institution in London and J. J. Berzelius (1779-1848) the atom had an internal structure, as spectroscopy seemed in Sweden, succeeded in decomposing numerous chemical to suggest. compounds with an electric current, the identity of the attractive force as electrical seemed complete. An electric cur- Of course, the increasingly empirical direction which rent separated a chemical compound into its elementary chemistry had taken in the last half of the 19th century constituents; an electric cell produced its electricity only with troubled both physicists and chemists. In 1881, Hermann von an accompanying chemical change. Helmholtz (1821-94), in a well-received annual Faraday Ad- dress before the London Chemical Society called for a return The model which illustrated most clearly an atom's elec- to the earJier electrochemical ideas of Berzelius which sug- trical behavior assumed that certain atoms were naturally gested the identity of the attractive force and electricity. "I electropositive, others electronegative, and that the attraction think the facts leave no doubt," Helmholtz said, "that the very between them explained the well-known attraction of unlike mightiest among the chemical forces are of electric origin. The charges in large bodies. Berzelius in 1811 developed a much atoms cling to their electric charges, and opposite electric more elaborate electrical theory of attraction. He imagined charges cling to each other" (6). each atom to consist of one or more electric poles; the positive The Swedish chemist and later Nobel Laureate, Svante and negative electrical charges resided in opposite parts of his Arrhenius (1859-1927) in 1887 argued that his electrolytic atom like the poles of a magnet Attraction between atoms experiments with aqueous soJutions also indicated that the resulted from neutralization of the opposite electrical charges atom's attractive force was electrical (7). Arrhenius showed at the poles (4). that, in solution, electrically active molecules were identical Electricity was the rage of the early 19th century, and the- with chemically active molecules. He had reduced chemical

Volume 61 Number 3 March 1984 185 and electrical activity to the same cause—the presence of In Germany, the chemist Richard Abegg (1869-1910) by charged atoms. But in spite of the reasonable arguments of 1904 had already developed an electrostatic theory of atomic Arrhenius and Heimholtz, conclusive evidence on the role bonding that was identical to Thomson's (15). His "rule of played by electric charges in the union of atoms was still eight" gave some indication of the maximum number of lacking. Indeed, the evidence did not appear until 10 years electrons involved in atomic union (15). Abegg observed that later. the same atom in its different compounds had either a positive In that year, 1897, J. J. Thomson (1856-1940), the physicist or. a negative charge and that the sum of the two was often who directed the Cavendish Laboratory at Cambridge Uni- eight. Chlorine had a -1 charge in sodium chloride (NaCl) and versity, England, demonstrated in his research on the elec- a +7 charge in perchloric acid (HC1O4); nitrogen's charge was trical conductivity of rarefied gases that atoms were not, as -3 in ammonia {NH3) but +5 in nitric acid (HN03). Accord- previously believed, indivisible. Instead, they contained ex- ing to Abegg, most atoms thus had available for bonding ceedingly light particles of electricity (8). These sub-atomic anywhere from one to eight electrons. Abe'gg's rule was the particles, later called electrons, were removable and carried first publication dealing with the number of bonding electrons a negative charge (9). As the 20th century dawned, it became (valence electrons) an atom contained and enjoyed great increasingly clear that all atoms contained one or more iden- popularity among physical chemists. tical, negatively-charged electrons and that the electron, be- Indeed, the efforts of Noyes, Abegg, and other physical cause of its small mass, rather easily moved from one kind of chemists to move chemistry away from its empirical and de- atom to another. scriptive state generally received a warm reception although G. N. Lewis in describing the origin of his electrical theory of Early Twentieth Century Theories of Electrical Attraction the atom wrote (16) J. J. Thomson lost little time in pointing out that the electron was responsible for an atom's electrical attraction. He I went from the Middle-west to study at Harvard, believing that at that time it represented the highest scientific ideals. But now I proposed his theory in papers published in the Philosophical very much doubt whether either the physics or the chemistry de- Magazine (10) and in the Silliman lectures which he gave partment of that university furnished real incentive to re- while visiting Yale University in May of 1903 (11). An at- search A few years later J1902], I had very much the same traction between two atoms, Thomson said, resulted whenever ideas of atomic and molecular structure as I now hold, and I had one of the atoms donated an electron to the second atom. As a much greater desire to expound them, but I could not find a soul one of the atoms now contained an extra electron, it was sufficiently interested to hear the theory. There was a great deal negatively charged; the other atom, having lost the electron, of research work being done at the university, but, as I see it now, carried a positive charge; and the two oppositely charged the spirit of research was dead. atoms then attracted one another. Thomson's theory of attraction was, of course, similar, though on a sub-atomic level, The opponents of the new theoretical or physical chemis- to the long-established law of attraction that governed the try were clearly a minority, however. Their opposition was also macroscopic behavior of bodies. short-lived. Lord Kelvin (1824-1907) refused to accept that interactions between atoms were electrical. He was an avowed Other physicists, among them Oliver Lodge 0851-1940) opponent of the electrical theory of matter applied to chem- in Britain and Johannes Stark (1874-1957) in Gottingen, istry and believed in a Boscovichian law of force as the ulti- discussed the electrical structure and attraction of atoms in mate explanation of the behavior of chemical atoms. Kelvin their publications. Lodge wrote in his monograph, "Modern agreed with Roger Boscovich (1711-87) that atoms were really Views on Matter" (12): points or identical centers that reacted according to an oscil- ... it becomes a reasonable hypothesis to surmise that the whole latory law in which the force between atoms varied (with of the atom may be built up of positive and negative electrons in- distance) from an attractive to a repulsive force (17) terleaved together, and of nothing else; an active or charged ion having one negative electron in excess or defect, but the neutral We might be tempted to assume that all chemical action is elec- atom having an exact number of pairs. The oppositely charged tric, and that all varieties of chemical substance are to be ex- electrons are to be thought of on this hypothesis as flying about plained by the numbers of eiectrions required to neutralize an inside the atom, as a few thousand specks. atom or a set of atoms; but we can feel no satisfaction in this idea when we consider that great and wild variety of quality and af- In his 1903 publication, "Dissoziierung und Umwandlung finities manifested by the different substances or the different ehemischer Atome," Stark suggested that chemical union 'chemical elements;' and as we are assuming the eiectrions to be resulted from the sharing of an electron by a pair of atoms in all alike, we must fall back on Father Boscovich, and require him a molecule. He represented the sharing with electrical b'nes to explain the difference of quality of different chemica] sub- of force that ran from the electron to each of the bonded stances by different laws of force between the different atoms. atoms. The electron attached itself with a larger number of lines to the more negative atom and with a smaller number to In the United States, the well-known chemist Edgar Fahs the more positive atom (13). Smith (1856-1928) at the University of Pennsylvania looked upon physical chemistry as something that chemists should Chemists who belonged to the new school of physical acknowledge rather than believe in (18). Louis Kahlenberg chemistry also examined the atom's electrical behavior. These (1870-1941) at the University of Wisconsin remained skeptical chemists believed that their science required more than pre- of electronic theories (19) paring new compounds and cataloguing their behavior. Like the physicists, they placed before themselves the much higher The eiectron theory considers electricity itself to be material in ideal of gaining a clear insight into the electrical atom and the character and to consist of corpuscles or electrons that weigh forces acting within it. about 0.0005 as much as a hydrogen atom. This theory has devel- Wiliiam A. Noyes (1857-1941) then at the Bureau of oped from a study of radium rays and the discharge of electricity Standards, expressed the physical chemists' conviction in an through rarefied gases. The electrons are considered to be nega- address he delivered to the International Congress of Arts and tive electricity itself. Positive electrons appear to be much more Sciences in St. Louis in 1904 (14) difficult to isolate. J. J. Thomson has recently attempted to construct a theory that the atoms of the various elements are com- Chemists should not be content with rounding out organic chem- posed entirely of electrons, and has shown that, on the basis of istry as a descriptive science nor even with adding to the numbeT such an assumption, the properties of the elements would exhibit of empirical rules which enable us to predict certain classes of periodicity aa indicated by the periodic system. The electron phenomena. We must instead, place before ourse!ves the much theory has not yet been tested as to its vaiue in the study of chem- higher ideai of gaining a clear insight into the nature of atoms and ical changes. molecules and of the forces or motions which are the real reason for the phenomena which we study. Thus, by the close of the first decade of this century.

186 Journal of Chemical Education mainly through the efforts of J. J. Thomson in England, before abandoning his search in 1921 (22). Harry Fry invented Richard Abegg in Germany, and an outstanding group of new types of electrical compounds called electromers which physical chemists at the Massachusetts Institute of Tech- he claimed proved the existence of charged atoms in organic nology which included G. N. Lewis, chemists and physicists compounds. According to Fry, electromers were compounds had arrived at the following picture of the structure of whose atoms had the same arrangement, but opposite elec- matter: trical charges (23); 1) matter consisted of divisible atoms, 2} every atom contained one or more nearly weightless, negatively H*—-Cl H —*C1 charged particles called electrons, 3) every atom contained a second kind of particle, considerably heavier than the electron, that accounted for most of the atom's "Cl Cl' mass and had sufficient positive charge to balance the electron's negative charge. cr—-NV--C1 cr—-N:—*ci 4) the transfer of electrons produced the attractive force holding electromers of hydrogen chloride and nitrogen trichloride atoms together. The use of the electron to account for the bond between Julius Stieglitz argued that the elusive charged atoms of or- atoms gave rise at this time to considerable debate between ganic compounds were different from those of inorganic physicists and chemists. The issue was whether an atom's compounds and incapable of isolation (24). electrons were stationary or in motion; in other words, was the Tne evidence was, however, overwhelmingly against the atom's electronic structure static or dynamic? Certain physical positive-negative theory when applied to organic compounds problems, those relating to atomic spectra, as well as the (and to certain inorganic compounds which chemists and physicists' fundamental problem of accounting for the atom's physicists had shown not to consist of charged atoms). Stuart stability clearly dictated a dynamic atom. The planetary atom Bates (1887-1961) at Illinois (25), Roger Brunei (1881-1924) that Niels Bohr (1885-1962) proposed in 1913 dealt essentially at Bryn Mawr College (26), and G. N. Lewis, by then at with these problems (20), As it happened, the chemists' major Berkeley (27) summarized the evidence in their papers on the goal, to explain the union of atoms, received from G. N. Lewis chemical bond. They pointed out that polar compounds in 1916 a clever and resourceful, but expedient, solution which generally liberated their charged atoms in solution and were did not question the atom's structure and thus the ultimate electrolytes, while nonpoiar compounds were not. Polar structure of the chemical bond. compounds, when compared to nonpoiar compounds, usually When J. J. Thomson put forward his theory that a bond had higher dielectric constants, larger dipole moments, and between two atoms occurred when one of the atoms donated greater specific inductive capacities. They argued that the two an electron to the second atom, chemists in the United States classes differed so significantly in their physical and chemical and abroad gave it a favorable reception. Among his earliest behavior that one could not possibly claim any similarity in American supporters were K. George Falk (1880-1953) and their electrical structures. But Lewis alone in 1916 proposed his school at Columbia University, William A. Noyes at the the first successful alternative theory of the electron's role in University of Illinois, Harry S, Fry (1878-1949) at the Uni- nonpoiar bond formation (28). versity of Cincinnati, and Julius Stieglitz (1867-1937) at the University of Chicago. In numerous papers published mainly in the Journal of the American Chemical Society from 1909 The Contribution of 6. N. Lewis: The Shared Electron Pair to 1917, they carried out a systematic application of Thom- In his theory of bond formation, Lewis assumed that instead son's theory to numerous chemical compounds (21). of the electron's complete transfer from one atom to another, The theory was often called the positive-negative theory as in the positive-negative theory, only a partial or incomplete because, as a result of combination, each of the atoms in a transfer of two electrons, one from each of the combining compound always contained either a positive or a negative atoms, occurred. The two atoms shared a pair of electrons charge. It worked exceptionally well for polar or inorganic between them. The electron pair attracted and held to it the compounds, those resulting from the union of a metai with a resulting positive cores of the combining atoms but belonged nonmetal. In forming the compound, sodium chloride, for to neither. This eliminated the formation of oppositely example, the metal, sodium, transferred one of its electrons charged atoms in compounds whose physical and chemical to nonmetallic chlorine. The sodium was now positive, Na+, properties gave no indication that they contained charged the chlorine negative, Cl~, and the resulting attraction of two atoms. With his theory of electron sharing, Lewis had over- oppositely charged atoms held the compound together, come the major shortcoming of the positive-negative theory Na+—~C1. Since chemists could demonstrate experimentally when applied to nonpoiar compounds. with electrolysis the actual presence of positive sodium and negative chlorine atoms in sodium chloride, the theory's H+—-Cl H:C1 fundamental postulate seemed verified. (A) (B) electron structures of hydrogen chloride (A) according to the positive-negative theory (B) according to Lewis, where each dot represents a shared elec- IT—"Cl cr-—icv--ci IT-X:--H I tron -a Lewis also pointed out that his theory could account just iiydrogen chloride methane carbon tefcraehloride as well for the formation of polar compounds, those known to Examples of Electron Structures According to the contain oppositely charged atoms. For each bond formed Positive-Negative Theory between two atoms in a polar compound, one of the atoms always had a much stronger attraction for electrons than the It was the application of the positive-negative theory to the other, and according to Lewis, a much greater share of the compounds of organic chemistry or to nonpolaT compounds electron pair. Indeed, in the extreme case the electron pair that led to serious difficulties. Atoms with positive and neg- belonged to it completely. This atom, therefore, appeared ative charges should have existed in those compounds also, negative, the other, positive. The positive-negative theory of but every attempt to establish their presence proved a failure. combination was then only a special case of Lewis' more William A. Noyes tried for 20 years to isolate these atoms general theory.

Volume 61 Number 3 March 1984 187 The reason why the Lewis theory required two electrons in wick (1873-1952), Ralph H. Fowler (1889-1944), and Thomas forming a chemical bond and not some other number was a Lowry (1874-1936), gave a favorable reception to the shared direct consequence of the static atomic model Lewis had electron pair (3.5). Sidgwick applied the theory successfully adopted. By 1916 chemists recognized that moat chemical to a previously troublesome class of chemical compounds compounds contained an even number of outer or valence called coordination compounds and wrote a well-known electrons monograph that contained a masterly presentation of Lewis' ideas (36). Number of Valence fotai Number of Valence But the greatest exponent of the Lewis theory was Irving Electrons in Atom Electrons in Molecule Langmuir (1881-1967), a research chemist at the General NH3= 8 Electric Company in Schenectady, New York. In the two-year H-I period, 1919-1921, Langmuir wrote extensively and lectured C = 4 widely on the Lewis theory in the United States and abroad H = l (37). His interesting and convincing personality and his admirable methods of presentation clearly aided the theory's acceptance. Indeed, following Langmuir's popularization of S0 = 24 the Lewis theory, chemists sometimes called it Langmuir's 0 = 6 3 theory, or the Lewts-Langmuir theory of valence (38).l This CC1, = 32 obvious neglect of Lewis, the author of the shared electron pair Cl = 7 theory, resulted in a long-lasting grudge between the two men. Lewis believed that Langmuir had never observed the estab- Lewis showed that he could easily account for their structures lished rules of priority regarding the origin of the theory (40).2 if each of the combining atoms shared two electrons each time In a letter to Langmuir in 1919, Lewis wrote (43) it formed a chemical bond with another atom. His theory thus provided a satisfying picture of the electronic arrangements ... to be perfectly candid I think there is a chance that the casual in numerous compounds. The Lewis theory also solved several reader may make a mistake which 1 am sure you would be the last other long-standing structural problems that had proved to encourage. He might think that you were proposing a theory embarrassing to chemists, those of ammonium chloride and which In some essential respects differed from my own, or one the oxyacids, and predicted correctly the structures of a re- which was based upon some vague suggestions of mine which had cently discovered class of compounds, the metallic hy- not been carefully thought out It seems to me that the views drides. which I presented were about as definite and concrete as was pos- To express conveniently and clearly his theory of the shared sible considering the condensed form of publication. I thick if any confusion should arise it would be due to points of nomencla- electron pair bond, Lewis proposed a new electronic symbol- ture. For example, while I apeak of a group of eight, you speak of ism now known as electron dot or Lewis formulas. Each pair an octet. of dots or colon placed beside a chemical element's symbol represented the pair of electrons that constituted the bond The dispute with Langmuir had one favorable conse- {28}. In short, the theory's great serviceability accounted for quence; Lewis recognized that chemists had forgotten who had its success, for within 10 years of its introduction in 1916, originated the theory. Langmuir had almost completely chemists had universally accepted the Lewis theory. overshadowed Lewis. This turn of events more than anything else led Lewis in 1923 to publish his classic monograph on the In 1918 F. Russell von Biehowaky (1889-1951) who had 8 studied under Lewis at Berkeley devised a theory of color for theory of the shared electron pair bond. Entitled "Valence inorganic compounds based on the Lewis valence theory. He and the Structure of Atoms and Molecules" (45), Lewis' lucid was also the first after Lewis to use the dot notation to rep- and concisely written book was required reading for chemists resent the chemical bonds in a molecule (29). The following in its day. A monograph which Lewis claimed in the preface year Joel HOdebrand (1881-1983), Lewis' longtime colleague would soon belong "to the ephemeral literature of science," at Berkeley, adopted the Lewis theory and electron dot became instead a classic in the history of chemistry. "Valence" notation in his textbook, "Principles of Chemistry" {30). In contained not only all of the ideas Lewis presented in his 1916 1920 two other Berkeley colleagues, Wendell Latimer paper but also those which very likely would have appeared (1893-1955) and Worth Rodebush (1887-1959), used Lewis' before 1923 had World War I not occurred. Its contents in- theory when they introduced the idea of a hydrogen bond in cluded the Lewis theory of acids and bases (the electron pair their discussion on the association of liquids (31); while Robert acceptor, electron pair donor theory), an examination of N. Pease (1895-1964) at Princeton analyzed in a 1921 publi- double and triple bonds in molecules, and a discussion on the cation the molecular volume of water, ammonia and methane source of chemical affinity which Lewis still believed to be according to the Lewis valence theory (32). magnetic in origin. Even today the fundamental ideas Lewis presented in his monograph remain correct. Other chemists in the United States, among them another Berkeley graduate Ermon D. Eastman (1891-1945), Ernest C. Crocker (1888-1964), Wallace H. Carothers (1896-1937), James B. Conant (1893-1978), and Howard J. Lucas (1885- ' In this regard see Joel Hiidebrartd's comparison of Lewis and 1963), began applying the Lewis theory to the reactions of Langmuir (39). "Lewis was an Indoor man, an omnivorous reader, much organic compounds in the 1920's. Some of the investigations given to reflection, a scientific philosopher. Langmuir frequented the out-of-doors; he observed natural phenomena with a keen eye. In his they carried out were the study of the electronic structures of Hitchcock lectures he told about lying on the ice of Lake George studying double- and triple-bonded molecules, the addition reactions with a magnifying giass a curious pattern of bubbles he had noticed In of the double bond, the addition compounds of ketones and the ice. I could not imagine Lewis doing anything of the kind.... the structures of aromatic molecules (33). Indeed, Lucas and Langmuir's mind was the more inductive; that of Lewis was more de- Archibald Y. Jameson (1902-1935) at the California Institute ductive." of Technology demonstrated convincingly in 1924 that the 2 Langmuir seemed to give Lewis some priority when he wrote in electron pair theory was far superior to the positive -negative 1919(47): 'This theory, which assumes an atom of the Rutherford type, polar theory in accounting for the addition and rearrangement and is essentially an extension of Lewis' theory of the 'cubical reactions of organic molecules (34). In the period 1924-26 atom' " Again, in 1920 Langmuir wrote (43): "This work of Lewis Lucas and his collaborators provided the evidence that led to has been the basis and the inspiration of my work on valence and atomic the extensive development and firm establishment of the structure." electron pair displacement theory (33). 3 Lewis was at first somewhat reluctant to write his monograph on "Valence" as he was already committed to writing his textbook on British chemists and physicists, among them Nevil Sidg- "Thermodynamics" {44).

188 Journal of Chemical Education There is little doubt that by 1932 Lewis' publications on the Within a few years, in 1931, Pauling gave a formal quan- electronic structures of atoms and molecules and their tum mechanical proof to the Lewis idea that a pair of electrons chemical reactions did much to convince the chemical com- constituted the nonpoSar bond (56). Quantum mechanics has munity to acknowledge the superiority of his valence theory. subsumed the Lewis electron pair bond; but because of William A. Noyes, a leading advocate of the polar or electro- quantum mechanics' mathematical complexity, chemists still static valence theory, accepted the Lewis theory in 1921 (46). use the Lewis theory on a working level. It remains today the In 1920 and 1921, K. George Falk published two monographs, foundation of modern valence theory. "Chemical Reactions: Their Theory and Mechanisms" and "The Chemistry of Enzyme Actions," in which he still adhered Literature Cited to a polar theory of valence (47). But by 1924, in the intro- (1) For a complete discussion of this topic aee Stranges. Anthony N.r "Electrons and Va- duction to the second edition of "The Chemistry of Enzyme lems: Development of the Theory, 1900-1925," Teraa A&M University Press, College Station, IX, 1*82. Actions," Palk had also accepted the Lewis theory. The Lewis (2) Volta, Alesaandro, "On the Electricity Excited tjy the Mere Contact of Conducting electron pair theory, he wrote, was proving extremely useful Substances of Different Kinds," Philosophical Transaction* of the Rfyyal Society, as a classifying principle for chemical reactions and in devel- London, Sfl, 403 (19001. The same article appeared in Phil. Mag., 7,289 (1B00). (3) Nicholson, William, and Carlisle, Anthony, "Account of the New Electrical or Galvanic oping new lines of research (48). Apparatus of 9ig. Alow, Volta and Experiments Performed with the Same," Journal of Natural Philosophy, Chemistry and the Arts (Nicholson's Journal), 4,179 (1800); Nicholson, William, arid Carlisle, Anthony, "Experiments in Galvanic Electricity," Conclusion Phil. Mag.,7,3-17 (ISM). (i) BerzeliiiB, J. J-, "Esuai Bur h Theorie des Proportions Chimiqites et sur V Influence By the mid-'twenties, Lewis had placed the electron pair Ctiimiitue de I'Stlectriziti," Paris, 1S1». See also Russell, Colin A., "Berielius and theory of the chemical bond on a firm qualitative basis. But the Development of the Atomic Theory/' in "John Dalton and the Progress of Science," (Editor Caldwell, Donald S. L.), The University Press, Manchester, En- his idea had no theoretical basis until quantum mechanics eland, 1969, established its correctness mathematically. (6) TiWen,WiUiam,"CannijzBroMemomlLsdUire,"J.Cftcrn.Soc.r 101,1677 (19121. In 1925 Wolfgang Pauli (1900-58) in Hamburg enunciated (6) von ilelmholfg, Hermann, "The Modern Development of Faraday's Conception of his famous exclusion principle (49). According to this prin- Electricity," J. Chem. Soc., 38 277 (1881). ciple, no two electrons in an atom could have the same nu- (7) Arrhenius, Svante, "Development of the Theory of Electrolytic Dissociation," in "Nobel Lectures: Chemistry 1901-1912,11 Elsevjer Publishing Company, Amsterdam, merical vsiue for each of the four quantum numbers used to 10S6. describe an electron's energy siate. A pair of electrons having (8| Thomson, .i. J., "Cathode Rays," Phil. Mag., 14,293 (1897). identical values for the n, I, and m quantum numbers, had to (9) G. JohnBtoneStoney(lB26-19n), an Irish physicist, introduced the word electron to represent each of the negatively charged particles he believed oscillated within the have their spin axis, designated by the s quantum number, atom, in his paper "On the Cause of Double Lines and of Equidistant Satellites in oriented in opposite directions to one another, In other words, the Spectra of Oases," Scientific Proceeding* of the Royal Dublin Society, *,ftfl3 (1891). This was BJX ysars before J. J. Thomson actually isolated the electron, the two electrons were paired. Pauli's principle therefore (11)) Thomson, J. J., "Cathode Rays," Phil. Mog., 44,293 (189Ti; "On the Charge of Elec- limited the total number of electrons possible in an atom and tricity Carried by the Ions Produced by Ronlgen Hays," Phil. Mafl., it. 528 (18S8); permitted their correct distribution within each atom. Applied "On the Manses of the Ions in Gases at Low Pressures," Phil. Mag., 48, 547 to the hypothesis of electron pairing in the chemical bond, it (11) Thomson, J. J., "Electricity and Matter." Charles Scribner's Sons, New Yorfc. UOi. (12) Lod&e, Oiiver. "Modem Views on Matter," Clarendon Press, Oiford, 1903, p. 11. appeared equivalent to what Lewis had suggested in 1924. If. {13) Stark, Johannes, "Dissoziierung und UmwandlunB chermscher Atome," F. Viewed tmd the electrons in a nonbonded atom were paired, Lewis wrote, Sohn, Braunschweig, 1903, pp. 3-8. then a pairing also occurred between two electrons in different (14) Nojres. William A., "Present Problems of Organic Chemistry," Science, 30.490 (1904). Quotation ie from p. 501. atoms upon forming a oonpolar bond (50)< Indeed, Lewis' (15) Richard AhegE, "Die Valenz und das periodische System, Ver&ucb einer Theorie der shared electron pair consisted of two electrons in identical MolekUlverbindungen," Zeit. nworg. Chemie, 39,330 (1904); "Valency," B.A.A.S. Report, Leicester Meeting, 77,481. (1907). energy states except for their opposing or paired spins (51). (16) I

Volume 61 Number 3 March 1984 189 (32t Pease, Robert N., "An Analysis of Molecular Volumes Fran tlie point of view of the (41) Lai^muir, Irving, "The Structure of Atoms and the Octet Theory of Valence," r>rae. Lewis-Langmurr Theory of Molecular Structure, J. Amer. Cham. Sac., 43, 991 Nat. Acrt. Set, 6,252 (1919). (1921}. (42) Langmuir, Irving, "The Structure of Atoms and ils Bearing on Chemical Valnnee," -1. {33} Eastman, Ermon £. "Double and Triple Bonds, and Electron Structures in Un&Bturated a/ Ind. and Eng. Chem., 12,368 (1920); Works, VI, p, 98. Molecules," J. Amer.h Chem. Sac., M,438 (16221. Eastman was at Berkeley. Crocker(33) ,Lewis, G.N., letter to Irving Langmuir, July 9,1919, Lewis papers. Ernest C, "Application of the Octet Theory to Single-Ring Aromatic Compounds," (44) Lewis, G. N,, letter to William A. Noyes, September 30,1919, Lewis papers. J. Amer. Chem.,Soc., 44,1618 (19221. Crocker was at M.I.T. Carotiiert, Wallac(46e H.) Lewis. , G. Pi., "Valence and the Structure of AComs and Molecules," The-Chemical "The Double Bond," J. Amer. Chem. Sue., 4fl, 222B {1B24|. Carothers was at the Catalog Company, Inc., New York, 1923. University of Illinois. Conant, Jaroea 8., "Addition Reactions of the Carbonyl Group (46) Noyes. William A., "An Attempt to Prepare Nteo-Nnrofien Trichloride, It. The Conduct Involving the Increase in Valence of a Single Atom," J. Amer. Chem. Sac, 43.1705 of Mixtures of Nitrogen and Chlorine in a Flaming Arc," J. Amer. Chem. Soc., 13, {1921). Conant was at Harvard. Lucas, Howard J,, and Jameson. Archibald Y., 1774 (1921). As late ss 1928, fry had not abandoned the electrostatic ttteoty. "Electrin Displacement m Carbon Compounds, 1 Electron displacement versus \Chemieal Reoiews, 5,657 (192B)J. Alternate Polarity in Aliphatic Compounds," J. Amer. Chem. Soc., 46,2476 (1924)(47. ) Falk, K. George, ''Chemical Reactions: Their Theory and MeehaniamB." D. van Nos- LucaswDsatthe California Institute of TechnoloKyrllE>wardJ.Lucaa, Howard-),, trand Company, New York, 1921k "The ChemisWy of Enzyme Actions," The Chsnical and Moyee, HolJis W., "Electron Displacement in Carbon Compounds, II. Hydrogen Catalog Company. Inc., New York, 1921. Bromide and 2-Pcnttne," J. Amer. Chem. Six., J7,1459 (1925). Lucas, Howard(4B J.,) Falk, K. George, "The Chemistry of Enzyme Actions," 2nd ed., The Chemical Catalog Simpson, Thomas K., and Carter, James M., "Election Displacement in Carbon Company, Inc.. New York, !924, p. 1.7. Compounds. III. Polarity Differences in Carbon-Hydrogen Unions,"*/. Amer. Chem.(49) Paull, Wolfgang, "Ober denZusammenkang des Abachluss der Elehtronengruppen Sac., 17,1462(1826). Lucas, Howard J., "Electron Displacement in Carbon Com- im Atom nut ierKomplexstiuklur der Sprktren," Zeit. PhysHi, 31,766 (1926); "Zur pounds. IV. Derivatives of Benmne," J. Amer. Chem. Soc., 18,1827 (1926). QuantenmBchoTuk des magnetischen Elektrons,"Zeit. Physik, i% 601 (1927). (34) Lucaaand Jameson, "Electron Displacement in Carbon Compounds. I."; as cited in (50) Lewis, G. N., "The Magnetaehemical Theory," Chem. Ren., 1,231 (1924). t.33) ahove; for Jater developments see LIICBB' papers givonabovfl. ffil) Pauling, Linus, "The Shared-Elontion Chemical Bond," Proc. Wat. Acod. Sd., 14,359 (35) SOG "The Electronic Theory of Vatency. A Genera] toiactiaavm," Trans. Paraday Sue,, (1928). W, 451 (1923), for (lie comments of these and the oUwr participant such ae William (53) Heisenberg, Werner, "Mehrkorperpioblem und Beaonanf, in der Quantenraechanik," A. Noyes, Robert Robinson, Charles ft. Bury, 3. J. Thomson and Wilfiam H. Zeit. Physik, 38 [6], 411 (1926); Dirac, Paul, "On tJie Theory of Quantum Meehanira," Bragg. Proc. Roy. Soc,, A, [12 [8], 661 (1928). 1361 Sidgwiek. nevil, "The Electron Theory of Valency," The Clarendon Press, Oifbrd, (53) HeitJeF, Walther, and London, Frita, " Weckselwirkimg neutraler Atorne \ui4 ho- 1827. ' moupoiore Bindung noch der Quancinmechanik," Zeit. Physik, *4,455 (1927). (37) Langmuir, Irving, The Stiucture of Matter in the Collected Worite of Irving Langmuir," YoshiliatMi SuEiura improved the nialnematica of Heitter and London's work." Vber VI, (Editors: Suits, Guy, and Way, Harold K.), Pergamon Press, New Vorb, 1161- die Eigenschaften des Wos^erstof/mQlekata im Gmndzttetande," Zeit. Physik, 4S, (38) Lewis, G. N., letter to Arihur B. Lamb, January 13, 1920, Lewil Papers; Ref. (45), p. 484 (1927). 87. (54) London, Fritz, "Zur Quaittentheorie der hamdnpoiarert Valemzahlen," Zeit. Physik, (39) "Iruing Langmuir's Phuosopny of Science with en Introduction by J. H. Hildebrand," 48,455(1928). in "Langmufr. The Man and the Scientist," Pergamon Preaa, New York, 1M2, p, 234.(55) Ref. (5J), p. 360. This volume was also igsued as Volume XI3 of "The Collected Worke of Irvine (S6> Pauling, Ijniia, "The Native of the Chemical Bond. I. Application of Results obtained Langmuir." from tlie Quantum Mechanics and from a Theory of Paramagnetic Huspectibiljty (40) I-ewis, G. N., !e«er to Arthur B. Lamb, January 13.1920, Lewis papers. letter, G. N. to the Structure of Molecules," J. Amer. ChetK. Soc. 53,1366 (1931). LewistoWiUiam A. Noy^fld July 13,1926, Lewis pajwrs.

The Amazing Periodic Table The study of the periodic table is a vital part of any chemistry curriculum. It m surely the single most important tool available to organize the vast amount of chemicaHnformation known today. The typical introductory textbook describes the periodic table in great detail, but iittle or no attempt is made to point out how amazing it is that such a simple pattern exists in the first place. Students, and instructors, should realize that the relationships portrayed in tJie periodic table represent an incredible degree of order almost without equai in nature. I have developed a useful exercise to dramatize this point for my beginning students. I ask a dozen boys to fine up in front of the class in order of increasing height. The rest of the class is then told to look for patterns. For example, usuaily several boys are wearing glasses, and attention is focused on the students just to the right of each boy with glasses. Careful scrutiny does not reveal any consistent pattern of similarities among this group. After a few more attempts at pattern finding the boys are sent back to their seats with thanks. I then turn to the blackboard and list tic first 20 elements in order of increasing atomic number. The similarities of He, Ne, and Ar are noted. Then the elements just to the right of each of these elements are found to resemble one another, but with very different properties than the noble gases. Next the elements to the left of each of the inert gases are examined, and again they are found to have similar chemical properties. At this point I usually rewrite the list of elements in the usual periodic table format and continue to check for the presence of additional chemical families. At the end of this session students have a good idea of the experimental basis for tile periodic table, and an appreciation of how astounding it is that such unexpected order exists in the world. James Finholt Carlton Coilege Northflekt, MN 5S057

190 Journal of Chemical Education Abegg, Lewis, Langmuir, and the Octet Rule William B. Jensen Rochester insiitute of Technology, Rochester, NY 14623

Contrary to the virtually universal opinion of introductory (Table 1, row 1), he was able to illustrate the entire series using chemistry textbook authors, the octet rule was not invented bivalent oxygen as the test element (Table 1, rows 2 and 3), 1 by G. N. Lewis. Without a doubt Lewis' concept of the shared where the examples for the R.O4 (ssftXg) class were taken from electron pair bond played a key role in giving the octet rule its the triad of elements headed by iron, cobalt, and nickel and present form. However, Lewis himself remained curiously belonging to what is today called group VIII. ambivalent about the importance of the rule, and the recog- Mendeleev's second rule established a relationship between nition of the significance of the number eight in valence re- an element's maximum valence as measured relative to hy- lationships actually has a long history that extends back to the drogen and its maximum valence as measured relative to last quarter of the 19th century and the work of Mendeleev oxygen, asserting that their sum was never greater than eight on the periodic table. Though at first glance such ancient or- and that, indeed, for elements in groups IV through VII (so- igins might seem surprising, a moment's reflection on the called higher types) it was in fact equal to eight, In other necessary relation between valence and chemical periodicity words, if a given element of higher type bad a hydride of the makes this connection quite reasonable. form RH,i, its highest oxide necessarily had a formula of the form RgOe-it (Table 2). Early History of the Octet Rule Though receiving wide circulation through the medium of In 3871 Mendeleev {Fig. 1) published an extended review his extremely popular textbook, Mendeleev's initial obser- on the chemical and physical periodicity of the elements, which, in revised form, served as the core for the chapter on the periodic table in his classic textbook "The Principles of Table 1. Mendeleev's First Rule Chemistry" (1,2). Among the properties discussed was, quite Univalent: DV DV HADV3 TiADV j ri^DV5 HADVg riADV? DrlAfV l naturally, the topic of valencei and Mendeleev enunciated two Divalent: RsO RO RjO3 ROj R2O6 ROa R?07 RO4 rules relating periodicity and valence in which the number Example: K2O CaO B^Oa SIOj P2O5 SO3 ClgO7 OsO^ eight played a key role. The first of these limited the maximum valence displayed by a given element to one of eight possible Table 2. valence types, RXn (where R is the element in question and Mendeleev's Second Ride X a univalent ligand or test element) and, by implication, Hydritfe RH Oxide RjOe-,1 asserted that the maximum possible valence of any element n in the periodic table could never exceed eight. Although CK, C?04 ^ CO2 Mendeleev was unable to illustrate the entire series of maximum valence types using a single univalent test element SHj S2O6 3 S03 CIH CfeO, none OsO, 1 A review of 20 recently published introductory cojlege-level chemistry texts showed that all of them explicitly or implicitly attributeci the octet rtiie to Lewis.

Figure. 1. D. MenOsleev. Figure 2. R. kbegg.

Volume 61 Number 3 March 1984 191 vations on the role of the number eight in valence relations did with various experimental criteria for establishing the relative not receive further elaboration until 1902, when they came to polarity of an element's valence in a given compound. How- the attention of a 33-year-old professor of chemistry at the ever, near the end of the paper Abegg ventured some specu- University of Breslau named Richard Abegg (Fig. 2). Abegg lations on the possible origins of polar valence. Though not was originally trained as an organic chemist, taking a PhD adverse to the concept of both positive and negative electrons, under A. W. Hofmann in 1891 for a dissertation on amido- he tended to favor a unitary theory in which positive charge chrysene. However, shortly after graduation Abegg shifted to was due to electron deficiency, and within this context gave the field of physical inorganic chemistry, doing post-doctoral a simple and prophetic interpretation of his rule (6): work under Ostwald, Arrhenius, and Nernst, and eventually becoming Nernst's assistant at Gottingen. There he special- The sum 8 of our normal and contravalences possesses therefore ized in the electrochemistry of both simple and complex ions simple significance as the number which for all atoms represents and was naturally led to a study of those factors determining the points of attack of electrons, and the group-number or posi- the ability of an ion to form complexes and to speculation on tive vaience indicates how many of these 8 points of attack must the possible electrical origin of chemical valence (3). hold electrons in order to make the element electrically neutral. In 1899 Abegg published a joint paper with Guido Bod- Unlike most other chemists and physicists encountered in lander attempting to correlate the stability of complexes with the history of the octet rule, Abegg is now virtually forgotten, the "electroaffinities" of the constituent ions and these, in though there can be no doubt that his rule formed a key step turn, with the ions' redox potentials (4). In 1902, in the course in the development of both the octet rule and the electronic of a lecture at the University of Christiania, Abegg extended theory of valence (7). The rule was explicitly referred to by all this work to the more genera! problem of the origin and peri- of the pioneers in the field who followed Abegg and, indeed, odicity of chemical valence and postulated his at-one-time- served as the "chemical law of valence" against which they famous rule of normal and contravalence (5). tested their own theories of valence and atomic structure. The Reviving the earlier electrochemical dualism of Berzeiius most likely reason for Abegg's eclipse was his premature death and Davy, Abegg postulated that all elements were capable at age 42 in a ballooning accident, and it is tempting to spec- of exhibiting both a maximum electropositive valence and a ulate on how the history of the electronic theory of valence maximum electronegative valence and that the sum of the two might differ had he lived, especially if he had been able to was always equal to eight (Table 3). The maximum positive modify his initial commitment to an extreme dualism (which, valence of an element was identical to its group number N and given his training as an organic chemist, is not improbable). its negative valence to 8 — N. Whichever of the two valences Interestingly, at the time of his death, Abegg was, in true was iess than 4 corresponded to the element's normal valence Germanic fashion, in the process of editing an enormous (as exhibited in the vast majority of its stable compounds), multivolume "Handhuch der Anorganische Chemie" in which whereas the complementary valence corresponded to ita he was attempting to use his rule as a unifying theme to or- contravalence (as exhibited in less stable, rarer combinations). ganize the descriptive chemistry of the elements (8). For elements in group IV (e.g., silicon and carbon) there was Abegg's rule established an explicit connection between the no natural preference for either of the two valence types and numerical limits of valence and the electronic theory of mat- such elements tended to be amphoteric {a term introduced by ter, then in its infancy. However, it did not attempt to provide Abegg). Abegg was, of course, aware that in practice many an explicit model of atomic structure, contenting itself instead elements failed to exhibit the full range of their potential valences. Indeed, he noted that elements in groups t—III never exhibited their contravalences (thus in effect restricting his Table 3. Abegg's Rule of Normal and Contravalence (6) law to Mendeleev's higher types) and that in the other groups the tendency to do so generally increased as one moved down Gruppe: the group (compare, for example, fluorine, with just HF, to 1 2 3 4 E 6 7 2 iodine, with both HI and IF?). Noimalvalenzen +1 +2 +3 -1 ±4 -3 -2 Kontravatenzen (-7) <-6) <-5> +5 +6 +7 Mendeleev's original formulation of his hydrogen-oxygen rule was without electrochemical implications. His maximum valence was strictly a stoichiometric valence derived from the classic relation atomic weight valence = equivalent weight Within the context of Ahegg's theory, however, hydrogen became a test element for establishing an element's negative vaience, oxygen a test element for establishing an element's positive valence, and their sum a reflection of Abegg's rule of • normal and contravalences. Abegg's views were elaborated in greater detail in a long (50 pages) paper published in 1904 (6). Most of this paper dealt

2 in a short note published in 1902 (Chem, News, 64 (August 8,1902)) the British chemist Geoffrey Martin suggested thai Ihe recent discovery of various intermetaliic compounds by Kurnakov had finally revealed species in which BIB elements of groups l-lll displayed their maximum vaience (or contravalence in Abegg's terminology). Quite independently of Abegg, Martin generalized Mendeleev's earlier observations with the equation and statement: "Hence, V-, + V2 = 8, i.e., the sum of the highest and lowest degrees of valence with which an element acts towards other elements ts a constant whose value Is 8." Martin also noted that "An element tends to act toward radicals of like electrical sign with its highest vafence, but toward radicals of opposite electrical sign with its lowest valence," thus placing an electrochemical interpretation on Mendeieev's rule equivalent to that of Abegg. Figure 3. J. J. Thomson.

192 Journal of Chemicai Education with the vague concept of "points of attack." This deficiency was made up in large part by the work of the English physicist J. J. Thomson (Fig. 3). Ever since his discovery of the electron in 1897 (which for some peculiarly British reason he persisted in calling a negative corpuscle—a term more appropriate to Boyle and the 17th century than to 20th century physics), Thomson had doggedly pursued a workable electronic model of the atom. By 1907 his search had given birth to the famous ptum-pudding model and to at least four valuable concepts which, though no longer used in the explicit forms given them by Thomson, are nevertheless an implicit part of all currently accepted electronic theories of valence: 1) the concept of an electronic shell structure for the atom; 2) the concept that chemical valence is largely a function of only the outermost electronic shell; 3) the concept that chemical periodicity implies a periodic repetition of the outer electronic shell structure; and 4) the concept that the stability of the rare gases is connected with shell completion and that the valence of other atoms can be correlated with an attempt to attain similar closed-shell structures via electron transfer (9). In a manner unusual for a physicist, Thomson was quick to point out the chemical implications of his model, explicitly connecting it with Abegg's rule and in the process enshrining Figure 4. W. Kossel. the number eight as the central numerical deity of chemica! valence (JO). Summarizing his views in 1914, he also added model (though he was fully aware of the Bohr-Rutherford what would, with the gift of historical hindsight, prove to be model) than in accurate experimental counts of the total an interesting caveat {11). number of electrons per atom, data not available to Thomson in 1907. These he obtained from the work of the physicist A. We regard the negatively electrified corpuscles in a atom as ar- van den Broek and used to construct his now famous plot of ranged in a series of layers, those in the inner layers we suppose maximum positive and negative oxidation states for the first are so firmly fined that they do not adjust themselves so as to 57 elements (Fig. 5). This was a plot of the total electron count cause the atom to attract other atoms in its neighbourhood. per atom or ion versus its atomic number, with the values for There may, however, be a ring of corpuscles near the surface of the neutral elements themselves appearing along the diagonal, the atom which are mobile and which have to be fixed if the atom those for the elements in their maximum positive oxidation is to be saturated. We suppose, moreover, that the number of corpuscles of this kind may be anything from 0 to 8, but that when states appearing as extensions below the diagonal, and those the number reaches 8 the ring is so stable that the corpuscles are for their maximum negative oxidation states as extensions no longer mobile and the atom is, so to speak, self-saturated. The above the diagonal. number of these mobile corpuscles isi an atom of an element is equa! to the number of the group in which the element is placed on Mendeleev's arrangement. ... Thus we see that an atom may exert an electropositive vaience equal to the number of mobile corpuscles in the atom, or an electronegative valence * • equal to the difference between eight and this number. Each atom can, in fact, exert either an electropositive or electronegative valency, aad the sum of these two valencies is equal to eight. In this respect the theory agrees with Abegg's theory of positive and negative valency. ... It is possible that the • number of corpuscles which form a rigid ring may Ill depend to some extent on the number in the inner I rings, i.e. on the atomic weights of the elements, and ...ll i that for elements with atomic weights greater than forty (i.e., Ar) this number may not be eight. If this should prove to be the case, the sum of the positive and negative valencies for such elements would not be equal to eight.

Kossel and Lewis The year 1916 saw the publication of two ex- 10 TTtT! i tremely important papers on the electronic theory % of valence. The first, published in the March issue \: ittt of the Annalen der Physik, was by a 28-year-old physicist at the University of Munich named Walter Kossel (Fig. 4). Kossel's paper, or rather fjj ., his monograph (133 pages!), was an explicit attempt to deveiop and extend Abegg's valence views for relatively polar inorganic compounds using the electron transfer model briefly hinted at by Abegg near the close of his 1904 paper (in- ?. J « deed Abegg is explicitly cited by Kossel no less than 20 times (12). In keeping with this goal, ti'tt C 0 , S'A'C i 7 ^ Ana* 5 X la Kossel was less interested in an explicit atomic Figure 5. Kossel's plot o' maximum positive and negative oxidation states (13).

Volume 61 Numbers March 1984 193 This plot allowed Kossel to assess in one stroke the validity larization, Kossei's treatment of coordination compounds of both Abegg's rule and Thomson's suggestion that electron proved quite useful and was popular among European transfer was associated with attempts to attain a closed-shell, chemists up until the Second World War, though it never at- rare gas structure. As can be seen from the figure, both tained a similar popularity among American and British Thomson's postulate and AbBgg's rule held fairly well for the chemists (13). s- and p-block elements (using modern terminology) as in- The second 1916 paper, published one month after Kossei's dicated by the dumping of the oxidation states about the rare in the Journal of the American Chemical Society, was by a gas counts, and the symmetrical disposition of oxidation states 40-year-old, chemist at the University of Berkeley named G. on either side of the diagonal for elements in groups IV N, Lewis (Pig. 6) and, in contrast to Kossel's epic, was quite through VII. However, problems were readily apparent for the terse (22 pages) (14). Lewis had actually begun speculating d-bloek elements. Although the elements up to group VIII on the electronic theory of valence as early as 1902 (about the appeared to attain a maximum positive oxidation state cor- year of Abegg's lecture at Christiania) and had independently responding to a rare gas electron count, in the case of groups arrived at a dualistic electron-transfer model similar to IVA-VIIA (e.g., Ti~-Mn) they failed, in violation of Abegg's Abegg's. However, like Thomson, Lewis had also proceeded rule, to attain the corresponding negative states of their group 3 to develop a specific static model of the atom, which he called B analogs (e.g., Si~Cl), a fact which Kossel felt to be of a great the cubical atom, and had thus apparently also independently significance in differentiating the two classes of elements. arrived at the concept of periodically repeating electronic Beginning with group VIII there was an erratic variation shells and the concept of the relative stability of rare gas in the maximum oxidation state, culminating in a second structures (Fig. 7). asymmetrical clumping of positive oxidation states about the Fortunately Lewis became increasingly skeptical about the counts for the last members of the group VIII triads (e.g., Ni ability of the electron-transfer model to account for the rela- and Pd). Today we associate these dumpings with the at- tively nonpokr compounds of organic chemistry and by 1913 tainment of a pseudo-rare gas (n - l)d10 configuration. was willing to publish a paper stating his belief that two rad- However, since Kossel was using total electron counts, rather ically distinct kinds of bonds were required in chemistry, the than configurations, the 10-valence electron count became polar electron-transfer bond of typical ionic salts and some associated with Ni and Pd instead. This led Kossel to postu- kind of nonpolar bond to represent the valence stroke of late that these elements represented a kind of imperfect or structural organic chemistry (15). Largely for this reason, weakened analog of the rare gases as, like the rare gases apparently, Lewis was unwilling to publish his cubical atom themselves, they bridged the gap between one cycle of re- model. peating maximum oxidation states (e.g., K{I]-Mn[VIII]) and However, some time between 1913 and 1916 Lewis was able another (Cu[Ij~Br[VH]). The striving for a maximum positive to resolve his dilemma by using the cubical atom to arrive at oxidation state correspond ing to either a rare gas or pseudo- the concept of the shared electron pair bond (Fig. 8). The re- rare gas electron count was virtually universal. The striving sulting "simple assumption that the chemical bond is at all for a maximum negative oxidation state corresponding to a times and in all molecules merely a pair of electrons jointly rare gas electron count, however, fel! off rapidly as one moved held by two atoms" not only provided the missing bond to the left of the rare gases and was nonexistent in the case of mechanism for the nonpolar valence stroke, but also allowed pseudo-rare gas counts, thus accounting for the asymmetry Lewis to resolve the dichotomy of two distinct bond types "so in the behavior of the group A d-block elements. In no case did repugnant to that chemical instinct which leads so irresistibly the maximum oxidation state of an element exceed eight. to the belief that all types of chemical union are essentially one The rest of Kossei's paper was essentially an application of and the same," through his realization that the progressively the resulting ionic bonding model to the problems of coordi- uneven sharing of the electron pair between atoms of in- nation chemistry, the autoionization of protonic solvents, and the relative acidity and basicity of oxides. Also included were 3 According to IUPAC notation. some simple calculations using Coulomb's law and an attempt to visualize the resulting bonds in terms of Bohr's atomic model. When combined with Fajans' later work on ionic po-

Li Be B C Figure 7. Lewis' cubical atom (14).

Figure 8. Single and double electron pair bonds viewed using the cubical atom Figure 6. G. N. Lewis. (14,.

194 Journal of Chemical Education ereasingly different electronegativities could yield the ionic Like his predecessors, Lewis had recognized both the im- electron-transfer bond as a limiting case. portance of the number eight in valence relationships (which The idea that a chemical bond could result from the sharing he called the rule of eight) and its correlation with the at- as well as from the transfer of electrons was not unique with tainment of rare gas structures. However, within the context Lewie. The chemists A. L. Parson (16), W. C. Arsem (17) and of the ionic model, as formulated by Kossel, this correlation H. Kauffmann (18), as well as the physicists J. Stark (IS) and was only possible in the case of maximum oxidation states 5+ J. J. Thomson himself (I 1), had suggested similar ideas. The (e.g., P and Cl~ in PC1S). Attempts to construct ionic for- difficulty with all of these proposals, however, was that no mulas for lower oxidation state compounds failed to give ions reasonable restraints had been placed on either the total having either rare gas or pseudo-rare gas electron counts (e.g., number of electrons per bond or on the number of atoms that P3+ in PCI3). The importance of the shared election pair bond could share a common electron. As a consequence the resulting for the octet rule was that it allowed the extension of the rule models were too open-ended to be operationally useful. Lewis, to these lower oxidation state species as well as to purely ho- by restricting both the number of electrons per bond and the monuclear species such as CI2 and Na. In contrast, Kossel's number of atoms so bonded to two, provided the necessary formulation of homonuclear species precluded their obeying restraints to give a workable theory. Robert Kohler, who has the octet rule (e.g., N2) and, indeed, Kossel went so far as to studied the origins of the shared electron pair bond, has sug- suggest that the rule was limited only to polar compounds. gested that the concept resulted from Lewis' attempts to ac- Though Lewis was well aware of the implications of the elec- commodate the electron-sharing concepts of Parson and tron pair bond for the octet rule, their full exploitation was to Thomson within the context of his own dualistic cubical atom be largely the work of Irving Langmuir. model, and that the restraints so necessary to its success were a natural consequence of the geometrical restraints imposed Irving Langmuir by the cubical atom itself (20). Irving Langmuir (Pig. 10) was a 38-year-old research It is worth pointing out that Kosse! had also recognized the chemist at General Electric when he first began to write on the necessity of a nonpolar bond for organic compounds as well subject of Lewis' electron pair bond in 1919 {21). In the course as the concept of a progressive change in bond type. Early in of three short years he managed, in addition to numerous his paper Kossel had noted that the electron-transfer model popular lectures, to publish more than 12 articles, extending, was unsuitable for nonpolar organic compounds and that an refining, and popularizing Lewis' work. Lewis had originally electron-sharing model similar to Stark's would probably be restricted his discussion of the cubical atom and chemical required. Near the end of the paper Kossel proposed some bonding to the s- and p-block elements, feeling that the am- specific models using two-dimensional Bohr-Rutherford ring biguities then present in the chemistry and electronic struc- atoms in which all of the valence electrons (e.g., 10 in the case tures of the d-block elements made attempts to extend the of N2) were held on a common ring placed symmetrically be- model too speculative. Langmuir, in his first and most ambi- tween the two bonded atoms (Pig. 9). As the polarity of the tious paper (66 pages), published in the June 1919 issue of the bond increased, this ring was progressively displaced toward Journal of the American Chemical Society, attempted to the more electronegative atom, and in the ionic limit became remedy this defect (22), Through the use of 11 bask postulates its sole property. covering the arrangement of the electrons in isolated atoms and their preferential sharing in compounds, Langmuir un- dertook to deduce the entire structure of theoretical and descriptive chemistry. The full extent of his ambition is revealed in a popular lecture published in 1921 {23). Langmuir wrote Ar

W HCI

f CaO

* 8N

s*©-

y- Figure 9. The progressive change from ionic to covalent bonding in terms of Kossel's ring atom model ()2J. Figure 10.1. Langmuir.

Volume 61 Number 3 March 1984 195 These things mark the beginning, I believe, of a new chemistry, a Table 4. Examples ot Ungmulr's Octal Equation deductive chemistry, one in which we can reason out chemical relationships without falling hack on chemical intuition I think Species 2* n H i/= ya(8n-2»)+ H Structure that within a few years we will be able to deduce 90 percent of everything that is in every textbook on chemistry, deduce it as you NH 8 1 3 need it, from simple ordinary principles, knowing definite facts in a 3 regard to the structure of the atom. Nt CO 10 2 0 3 Despite his enthusiasm, Langmuir's extension of the static atom (Fig. 11) proved to be short-lived. By 1921 Bohr, on H2CO 12 2 ^ 4 the basis of spectral evidence (24) and Bury, on the basis of + chemical evidence (25), had shown that Langmuir's postulated NaCI 8 1 0 0 Na |ICll]- shell sequence of 2,8,8,18,18, and 32 electrons was wrong as was his postulate that a new electron shell could be started CS2 16 3 0 4 only if the preceding shells were completely filled. In addition, most theoretical physicists, who by this time were firmly committed to a dynamic atom model, were less than impressed by Langmuir's extended static model. The German physicist muir to replace Lewis' more cumbersome "rule of eight") Sommerfeld characterized Langmuir's 11-postulate deductive Se = 2s - 25 (2) chemistry as "somewhat cabalistic" (26), and the English physicist E. N. Andrade was even more blunt (26), where 2e is the total sum of available valence electrons in a species, Ss is the sum of the valence eiectrons required for It is scarcely necessary to insist on the artificality of this picture complete shell formation for each of the heavier atoms (i.e., The electrons in Langmuir's atom have, in fact, so few of the excluding hydrogen), and B is the number of covaient bonds known properties of electrons that it is not immediately clear why between the heavier atoms. Restriction of the heavy atoms to they are called electrons at all. those lying below Ar converts eqn. (2) into the major equation Thus, in actual practice, Langmuir's development of Lewis' of Langmuir's "octet theory" model was restricted to the same atoms as Lewis had originaily discussed. Nevertheless, a number of valuable concepts did Ze = 8n - 2B (3) evolve out of Langmuir's refinements, including the electro- when n is the number of heavy atoms requiting octet com- neutrality principle and the isoelectronic (isosteric) principle pletion. Addition of the covalent bonds, H, to any protons (27), the last of which has been characterized by Kober, in a present gives the final total number of covalent bonds in a recent article, as the "last important nonquantum mechanical species bonding principle" (28), Even more important to the present discussion was Lang- H + B = H + -<8» - 2e) (4) muir's use of his postulates to deduce a general mathematica! expression for the "octet" rule (a term introduced by Lang- Some example applications of eqn. (4) are shown in Table 4

CHJI-T 1,- Stliutt*tiaB Iht I*KiLj*afiu4r Thorny at AT-JEnfe Hiiueture. Figure 11. Langmuir's sxlentted cubical atom models (from Washburn, E. w., "Introduction !o Hie Principles of Physical Chemistry," aid sd., McGraw-Hill. New York, 1921, p. 470.)

196 Journal of Chemical Education and some examples of Langmuir's original structures in Figure introduced by Langmuir. In the latter case, Langmuir further 12. distinguished between those species obeying the octet rule In 1921, in what was essentially his last major paper on the proper (i.e., 2s = 8n) and those obeying an extended rare gas octet theory, Langmuir gave a comprehensive survey of the rule (i.e., s = 18), the former being restricted to combinations limitations of eqn. (4) (29). By this time he had succeeded in among elements corresponding to Mendeleev's higher types reducing his original 11 postulates to three, the third of which and the latter being the first explicit statement of the 18- represented the first explicit statement of the electroneutrality efectron rule much beloved of the organometallic chemist. principle On the other hand, the "incomplete compounds" of Class II failed to obey postulate I and thus the octet rule. In Lang- 1) The electrons in atoros tend to surround the nucleus in succes- muir's opinion this was because shell completion in these sive layers containing 2, 8, 8, 18, 18, and 32 electrons respec- species required, in violation of postulate 3, the buildup of tively. 2) Two atoms may be coupied together by one or more duplets held prohibitively large net ionic charges (and here Langmuir was in common by the completed sheaths of the atoms. generous in allowing charges as high as 6+ and 4— in contrast 3) The residual charge on each atom or group of atoms tends to a to Pauling's later restriction of 2± or lower). Finally, Langmuir minimum. included a class of "exceptional cases" whose bonding apparently required a special kind of electron-sharing beyond Shell completion was desirable because it resulted in a that proposed in postulate 2. spherically symmetrical electron distribution which tended to minimize external electrical fields about the atom. Mini- The Debate mization of the residual charges was also desirable because it minimized the coulonibic energy required to maintain charge Lewis' opportunity to comment on Langmuir's work came separation on adjacent atoms, in 1923 with the publication of his classic monograph, "Va- Langmuir pointed out that the requirements of postulates lence and Structure of Atoms and Molecules" (30), With the 1 and 3 were frequently in conflict and used this conflict to exception of a short retrospective essay written in 1933 (31), rationalize the limitations of his octet equation. His resulting this was essentially Lewis' last major contribution to the classification of chemical compounds is shown in Table 5. electronic theory of valence and represented his matured views Species obeying postulate 1 were termed "complete com- on the nature of the electron-pair bond. pounds" and tended to obey the octet rule either through the Already in his 1916 paper, Lewis, faced with the inability formation of ionic compounds {Class IA) or through the forof the cubical atom to represent a triple bond and the over- mation of "covalent" compounds (Class IB)—another term whelming evidence of organic chemistry that the valences of carbon were tetrahedrally directed, had speculated that the electrons of the cubical atom were drawn together to form a tetrahedron of electron pairs (Fig. 13). By 1923 Lewis had also abandoned his earlier defense of the static atom (32) and was willing to compromise with the dynamical atom models favored by the physicists, suggesting a mode! in which the electrons of the static atom corresponded to the average positions of electrons moving in small directional orbits. In keeping with these views, the cubical atom was presented only in an historical context in the 1923 monograph. Cubical

0 c 0

Figure 13. Lewis' tetrahedrai atom with close-paired electrons (14).

Table 5. Langmuir's Classification of Compounds via the Octet Rule

I. Complete Compounds A) Compounds Without Covalence \B = 0) 1) Electropositive main group elements (W < 3) pius electronegative N 0 elements (N £ 4|, e.g., NaCf, NB, AljQ) 2) Eariy transition elements in their maximum oxidation state plus electronegative elements, e.g.. ScCI3, TaBrs, CrFe 3| Certain halides ol the electronegative elements in their higher oxidation states, e.g., PCI6. SF6 B) Covalent Compounds 1) Armngtheeiectranegatfveelements, where s = B, («> 4), e.g.. C, N, O, F, Si, P. Cl 2) Among the transition elements, where s « 18. e.g., Fe

B) Salts ol the later transition elements, e.g., CrCi3, CuClj, ZnO III, Exceptional Cases A) Triply bonded species, e.g., Hi, CO, CN~ Figure 12, Some of the "cubical atom" molecular structures which Langmuir 8) Hydrogen-bonded species, e.g., HFj~ deduced using his octet equation (27). C) Boranes

Volume 61 Number 3 March 1984 197 Table 6. Lewis' Examples o( Species Violating the Octet Rule

1) Odd Molecules: NO,CISO 3 2) Electron Deficient: NaCH3, BR3, BF3, SOa, HPO3, COa ", NOa",

possibly even MaCi(g) ? 2 3) Electron Rich: F>CIS, SF6. UF6, SIFe -, FtCl6 -

Figure 14. Langmuir's cubteal structure for N2, CO, and CN [27). Lewis even included a chapter in his monograph dealing with "Exceptions to the Rule of Eight" in which he discussed the examples summarized in Table 6. In viewing this list one is struck by the fact that Langmuir's own discussion of this models of molecules, such as those used by Langmuir (recall subject was in some ways more thorough. Although the odd Pig. 12), were used nowhere in the book, extensive use being molecules in Class 1 certainly violate the octet rule, their made instead of the less structurally explicit electron dot supposed scarcity and high reactivity could be used to support formulas, though in several places tetrahedral atom models the stability of the octet just as well as the stability of the were also used. electron pair. On the other hand, all of Lewis' electron-defi- Langmuir's failure to abandon the cubical atom accounted cient examples and most of his electron-rich examples could for his classification of N , CO, and CN~ as "exceptional 3 be (and were) accommodated by Langmuir's octet equation cases." Lacking a triple bond, he was forced to postulate a by using an ionic formulation. Finally, several of the elec- special electronic structure for these species in which both tcon-rich examples were not fair game (e.g., PtClg2", UFe, and kernels were simultaneously enclosed within a single cube of Mo(CN)a4~) as Langmuir had never claimed that the octet' electrons, the remaining two electrons being shared as a nor- rule was valid for elements above AT. mal dupiet between the kernels (Fig. 14), a proposition which Lewis was to later characterize as "ad hoc" (30). Lewis' purpose was, of course, less to find examples which Though, as Kohler has suggested, the cubical atom probably could not be fitted by Langmuir's equation than to find ex- played a central role in the initial inception of the electron pair amples which could be fitted only by postulating structures bond, Lewis was quick to obtain an empirical base of support (usually ionic) which were at variance with their known for the bond, the most impressive evidence being the obser- physico-chemical properties. Indeed, in looking at the posi- vation that virtually all stable chemical species contained an tions taken by Larigmuir and Lewis regarding the octet rule, even number of electrons. Indeed, the few "odd molecule" one receives the impression that Langmuir, in his desire to exceptions to this rule tended to be highly reactive arid fre- emulate the rigor of physics, wished to be guided by the de- quently underwent dimerization reactions to give products ductions of his postulates, whereas Lewis, more open to the with even electron counts, Lewis also became increasingly experimental data base of chemistry, was more willing to be convinced, in large part through the influence of A. L. Parson's guided by the empirical evidence. magneton model of the atom, that magnetic interactions be- There is little doubt that the personal interaction between tween electrons were responsible for the formation of electron Lewis and Langmuir also tended to color the positions they pairs, a thesis discussed at length in a separate chapter of the took regarding the octet rule. Langmuirwas a popular and 1923 monograph and in a review published the next year (59). dynamic lecturer and Wilder D. Bancroft has left us with an These considerations led Lewis to postulate that the formation amusing picture of what it was like to be a member of one of of electron pairs or the "rule of two," as he called it, was a Langmuir's audiences {33). much more important bonding principle than the rule of eight and account, in part, for his evaluation of Langmuir's octet Langmuir is the most convincing lecturer I'have ever heard. I equation. Lewis wrote (30) have heard him talk to an audience of chemists when I knew they did not understand one-third of what he was saying; but thought they did. It's very easy to be swept off one's feet by Langmuir. The striking prevalence of molecules in which each atom has its You remember in Kipling's novel Kim that the water-jug was full quota of four electron pairs in the outermost shell has led broken and Lurgan Sahib was trying to hypnotize Kim into Langmuir to attempt to make the octet rule absolute, and he even seeing it whole again. Kim saved himself by saying the multipli- proposes an arithmetical equation to determine, in accordance cation table ... [so] ... I have heard Langmuir lecture when 1 with this rule, whether a given formula represents a possible knew he was wrong, but I had to repeat to myself "He is wrong, I chemical substance. I believe that in his enthusiasm for this idea know he is wrong, he is wrong" or I should have believed like the he has been led into error, and that in calling the new theory the others. "octet theory" he overemphasizes what is after all but one feature of the new theory of valence. The rule of eight, in spite of its great Naturally Lewis was initially quite pleased with the pub- importance, is less fundamentai tban the rule of two, which calls licity given his theory as a result of Langmuir's lectures and attention to the tendency of electrons to form pairs. papers. However, as time passed and more and more of the publicity accrued to Langmuir instead of Lewis, Lewis became Langmuir, on the other hand, felt that Lewis' neglect of increasingly upset, expressing his true feelings in a letter transition metal chemistry had misled him concerning the written to W. A. Noyes in 1926 (34). necessary instability of "odd molecules," and that their relative scarcity was due less to an inherent instability resulting Perhaps I am inclined to be too caustic in this matter, but I really from their unpaired electrons than to the relative abundance do feel that while people were justified in being carried away a bit of closed-shell species, or in Langmuir's own words (29) by Langmuir's persona! charm and enthusiasm some years ago, to persist, especially as they do in England, in speaking of the Lang- .. . the remarkable tendency, pointed out by Lewis, for roost com- muir theory of valence is inexcusable. pounds to contain an even number of electrons is due merely to the relative abundance of complete compounds compared to in- Another of Langmuir's talents was the ability to coin complete ones. In other words, the even number of electrons in catchy terminology, such as dupiet, isostere, octet rule, and most compounds results from the tendency of Postulate 1 [i.e. covalent bond, and it is not without note that the first two closed-sheii formation! rather than from any more general ten- terms do not appear in the index of Lewis' monograph and dency for electrons to form pairs. that the terms octet theory and covalence appear only once. Thus Langmuir viewed the prevalence of even-electron - In fact I^ewis recommended that the term covalent be dropped count species as a consequence oi1 complete shell formation because Langmuir had "associated this term with an arith- and as a reflection of the octet rule for elements lying below roetrieal equation by which he attempts to predict the exis- Ar, whereas Lewis viewed it (and the octet rule itself) as a tence or nonexistence of chemical compounds" (30). In private Lewis rather humorously expressed his resentment over the consequence of the "rule of two."

198 Journal of Chemical Education manner in which Langmuir had ignored Lewis' own termi- 7. Summary of Major Events In Development ot the Octet nology (34), Rule ... sometimes parents show a singular infelicity in naming their Mendeleev: 1871 children, but on the whole they seem to enjoy having the privi- Eight as a maximum valence rule and the sum of the hydrogen and oxygen lege. valences for higher types. Abegg; 1304 In public Lewis was, of course, less outspoken and in his Electrochemical Interpretation of Mendeleev's rule of eight In terms of electron 1923 monograph gave an evaluation of Langmuir's contribu- gain and loss. tions which can only be viewed as a masterpiece of diplomatic Thomson: 1904, 1907 understatement {30). Concept ot chemical periodicity In terms ot recurring outer electron configurations. Rule of eight as striving for completion of stable rare gas shells. it is a cause of much satisfaction to me to find that in the course Kossel: 1916 of this series of applications of the new theory, conducted with Extension of Ionic model. Eight as a maximum valence rule (or pofar com- ttie greatest acumen, Dr. Langmuir has not been obliged to pounds only. change the theory which I advanced. Hete and there he has been Lewis.- 1916 tempted to regard certain rules or tendencies as more universal in Continuity of bond type and electron pair bonding mechanism tor octet their scope than i considered them in my paper, or than I now completion. consider them, but these are questions we shall have a later oppo- Langmuir 1919-1921 runity to discuss. The theory has been designated in some quar- Elaboration and popularization of Hie Lewis model. Mathematical formulation ters as the Lewis -Langmuir theory, which would imply some sort ot the octet rule. of collaboration. As a matter of fact Dr. Langmuir's work has been entirely independent, and such additions as he has made to what was stated or implied in my paper should be credited to him alone. The debate over the validity of the octet rule did not, of course, end with Lewis and Langmuir. Between the 1920'a and In the final analysis there can be little doubt that Lang- the 1940's a number of vigorous discussions took place in muir played a key role in accelerating the acceptance of Lewis' which not only the validity of the octet rule was questioned electron-pair bond. Robert Kohler, who has studied the in- but the validity of the electron-pair bond itself (35-37), and teraction between Lewis and Langmuir in some detail, has aspects of this debate are still With us {38,39). More recent concluded that by 1920 the chemical community was still, by quantum mechanical calculations, however, have tended to and large, content to use the ionic electron-transfer bond and discount the importance of octet expansion and have rein- that no crisis in chemical bonding was evident which might stated the general validity of the octet rule for the p-block draw chemists to a model similar to Lewis' electron-pair bond. elements (40). In keeping with this conclusion, modern The widespread and rapid acceptance of the electron-pair bonding theory has also provided a satisfactory resolution of bond was rather a consequence of Langmuir's dynamic per- the problems associated with both electron-deficient and sonality and the unique manner in which he spanned both the electron-rich species and has done so in a manner which shows industrial and university chemical communities. As Kohler that neither Lewis nor Langmuir was totally correct in the has written (21) positions they took. Langmuir, in his desire to maintain the octet rule, was willing, in spite of the physico-chemical evi- What made the difference was, of course, Langmuir himself and dence, to postulate ionic structures for many of these species, his personal reputation. The new theory was well received be- whereas Lewis, in his desire to maintain the supremacy of the cause it was "Langmuir's theory" and not because of its intrinsic 2c-2e covaient bond, was willing to propose both hextet and intellectual worth. Once received, of course, its worth become evident. What I wish to stress is that the advantages of the new theo- expanded octet structures. The current consensus maintains ry were not immediately obvious and that had it not been "Lang- both the octet ruSe, on the one hand, and the presence of eo- muir's theory," the rediscovery and adoption of Lewis' theory valent bonding, on the other, by abandoning the explicit as- might well have awaited a real crisis in the theory of bonding. sumption of both Langmuir and I-ewis that the covaient bond must at all times be a localized two-centered bond. Thus Summary, Conclusions, and Prospects electron deficient species have been accommodated via the The major events in the development of the octet rule are closed 3c-2e bond popularized by Lipscomb for the boron hydrides (41) or via the use of delocalized x-electron systems summarized in Table 7, though obviously many additional 2 contributions were made by lesser-known chemists which (e.g., BF3, CO3 "", etc.), whereas electron-rich species (e.g., couid not be touched upon for lack of space.4 These events PCI5, XeFJ have been accommodated via the open 3c~4e bond allow one to draw at least three major conclusions about the popularized by Rundle (42), Pimentel (43), and others (44, origins and development of the octet ruie: 45).

1) Within the context of the dualistic or electrovalent model the The case of the d-block elements is more ambiguous. The octet rule essentially corresponded to a maximum valence rule generalized fare gas ruie first hinted at by Langmuir was in- only. While the striving for a rare gas structure determined bodi dependently formulated by the English chemist N. V. Sidg- which elements could exhibit negative valences and the value wick in 1923 (46). Sidgwick, however, preferred to use total of these valences, in Vac case of the positive valence it merely electron counts rather than valence electron counts and con- determined the maximum value, placing no necessary restric- tions on the lower values. sequently called his technique the effective atomic number rule (EAN). Not until 1934 did Sidgwick explicitly connect 2) The covaient model, by providing a means, via election sharing, of rationalizing both the lower positive oxidation states and his EAN rule with Langmuir's earlier 18-electron rule and homonuclesr species in terms of rare gas structures, substan- derive an equation, related to Langmuir's (though based on tially strengthened the identification of the octet rtiie with the total electron counts), for predicting the structures of poly- formation of rare gas structures. nuclear metal carbonyls and nitrosyls (47). Extensive appli- 3) At no time, within the context of either the electrovalent or cations of the EAN rule to the structures of metal carbonyls covaient model, was it claimed that the octet/rare gas structure were made by Blanchard in the 1940's (48) and the importance relation was generally valid for elements beyond Ar. of the rule exploded along with the field of organometallic chemistry in the late 1950's and 1960's, despite its many vio- lations. More recent theoretical work has provided both 4 Some minor contrRwtians, thouc/i hardly tiy tesser-known chemists, quantitative {49) and qualitative (50) rationales for why the include Die work of Ramsay and Nernst. Ramsay was one of the first 18-electron rule is weaker than the octet rule. to apply Abegg's rule of eight, and Nernst expressed some suggestive views on the saturation of ions. For a discussion, see Stranges {7). Even Langmuir's arithmetical equation is still with us and

Volume 61 Number 3 March 1984 199 in modified form is used extensively in the field of solid-state Table 8. Examples of the Generalized 8 - N Rule chemistry. If one applies eqn. (3) to only the more electronegative or anionit components of a solid-state compound, Structural Array of one obtains Species • 2e, {2ea + fU'Og the Zlntl Atoms C 4 4 8 - 26. (5) P 5 3 S iU*Va] of Pi where 2e includes not only the valence electrons from the tetrahedron fl Se 6 2 8 anionic components but any electrons transferred from the a 7 1 8 CI; discrete pairs cationic components, nB is the number of anionic components Cs Sn S 3 8 (Sri*)4" tettahedra per unit formula, and 2Ba the number of anion-anion bonding CaC? 10 3 8 (IC3Ci)=~lr|pte bonded electrons. In general the anionic components are restricted discrete pair to elements lying to the right of the Zinti line in the periodic CaSfc 10 3 a £ [813/3]1 ~ table (i.e., groups IV-VII, again shades of Mendeleev's higher lap 6 2 8 types). Rearrangement of the equation and redefinition of 2Ba CaP 7 1 8 P^~ discrale pairs = 6H, gives Na/ S 0 8 Isolated l~

A Anionic Z-lttft atwns to italics.

(19) Stark, J.r "Diasoziierung und UnvandlLiiiH Chexnigcber Atome," ^ This is called the generalized 8 — N rule and is the subject of 1903, and many o&er papets and monographs. Stark'a work on the chemical bond is summarized inBu8glirR-,&"n"Eef. Chemisch.CkgmiBch-tech, Vartrdge, 19,(1913), an extensive literature (51-56). The equation can also be and in Hahn, D. A., and Holmes, M, E., J. Amer, Chart. Soc, 87,2611 (1915). applied to the structures of pure elements lying to the right (20) KohJer,R.E.,Hist.Stad.Phys.Sd.,i,343fIWl).S,431 (1B75);Brit.J,Hist.Sci.,S, 233 B9J5). of the Zintl line, Some example applications are shown in (21| Kohlut, R. E-, Hist. Stud. Pkys. Sci., 4,39 (1974). TableS. (22) Langmuir. I, J, Amer. Chem, SDC.,41,868 (1919). i23) Langmuir, L, Chem. Metoll. Bnn., 24,563 (1921). Extended versions of Langmuir's original equation have (24) Bohr, K,Nature, m, 104 (1921), also appeared in the literature which incorporate the possi- (26) Bury, C. R., J. Amer. Chem. Soc, 43,1602 (1821). bility of the multicentered bonds required for the description (26) Andrade, E. S, "The Structure of tiie Aloco," Haremirt Biaco & Co., New York, 1S23, pp.239-*0. of both electron-deficient (57) and electron-rich (58) (27) Unginuir.l.J, Amw. Chem. Hoc, 41,1543 (1919). species. (28) Kober, F.r Chem. Zat., l«, 1 (1&82). (29) Langrnuir,I..Science,S4,59(1921). Literature Cited (SO) Lewis, G. N-, "Valence and the Structure of Atoms and Molecules," Chemical Catalog, Co., New York, 1923. (1] Mendeleev, D., Ann., Suppl. VIII, 133 (1871), also J. Rust. Phy. Chem. Soc., (311,8) 0Lewis,G.N.,.f.CJiem.i%y5., 1,17(1933), (32| Ijiwis, G. K, Science, 46,297 (1817). (21 Mendeleev, D., "The PfUicipIos of Chemistry," 6th ed.. Longmans, London, 18W, Vol. (33) Bancroft. W. D., J. Phy. Chem., 35,1904 (1931). a, Chap. 16. (34) Quoted in Kohlsr (21). (3) Qaekgroutid on Abegg may be found in Arrhenius, S., Z. Electrochem., 16, &54 (1910)(35, ) Main Smith, J. B., "CheroiaCy and Alomic StnicUue," Van Nnstrand, New York, 1924, and Nernst, W., Berichte, 48,659 (1913). pp.123-125. (4) Abegg, R,, and Bodlander, G,, Z. Ann's- Chem., 20,453 U809), and Amer. Chem. J.,(36) Sugden, S., "The Parachoi and Valency." RflutledEe. London, 1MB, pp. 199-202. 28,220(1908). (57) Hunter, R, and Samuel, R-, Chem. list, S4.31, B3S (19351:5S, 733 (1936); also Samuel, (G) Abegg, Rr. "Varsuch einer Tbaoiie der Valena und der MoSekuJarverbindiingen," R.,J. Chem-Phys., 13,167 (1&44), and later pjtpen in the aawe aeries- Christiana Videnshabs-Selshabett Skri/ter, 12, (19021, aUoJ. Chem. Sac.(38 Abal.,) Petit,L.D.,Quart.Keu..2S, 1(1971). 84,536 (191)3). |39) Giltespie, R. J., "Molecular Goomelrjr," Van Nostnuid, London, 19)2. (6! Aiwgg, R., Z. Anorg. Chem., 39,330 (1904), also B.A.A.S. Report, 77,480 (1907), (40and) Couison. C. A., IVot^edings a) the Robert A. Welsh Foundation Conference of Chemical Scientia.i.H (1910). Besearch, XVI_, Theoreticat Chemistry, Houston, Texas, 1972, Chap. 3. (7) General bnckground on the history of the electronic theory of valence can be found in (41) Upscomb, W. N,, "The Boron Hydrides," Bonjamin, New York, f 963. BusaeiL C. A., "The History of Valency," Leicester University Press, Leicester, 1971. (43) Kundle, R. E, Ret: Chem. Prog., 2S, 195 (1963), also Sure. Prog. Chem., 1, SI and Sttftnges, A.M., "Electrons and Valence Development of the Theory, 1900-1925," (1963). Tesas A & M University PresB, College Station, Texas, SSS3. (43) Pimento), G. C, J. Chem. Phys., 19,446 (1951). (31 Abegg, K., and Auerhnch, F, (Editors), "Handbuch der Anorganiaehe Chrnnie," Hirael, (44) Mushet, J. L, Angsw. Chem. Int. Ed.; 8,54 (1969). Leipzig, 1908; four projected volumes. Actually at least 12 separata parls wete pub- (46] Komlkov, R. V,, in Kicnetaov, (iBdiior), "Theory of Valency in Pregras," Mir, Moscow. lished, some as late as 193a. The projected series was never completed. lS77,Chap. 10. i9) Thomson, j, J., "The Corpuscular Theory of Matter," Constable, London, 1907, Chap. (46) Sidgwkk, N. V., "The Elect™™Theory of Valenty," CSaiendon Press, Ojford, 1927, 6; also Phil. Mag, 7, 237 (1904). Thomson's earlier work is discussed by Stnnges Chap. 10; J. Chem. Svc., 123,725 (1923). (7>. (4V) Sidgwick.N. V., and Bailey, R. W.,Proc. Roy. Soe. (Londm), AU4.52I (1934). (10) SaMiinan. M.,.1. CHEM. EDUC SO, 59 (1973), (45) Blanchard, A. A., Chem. fief „ 21,3 (1937); S6,409 (1910). (tl) Thomson, J. J.. Phi?. Mag..27,751 (1914). (4S) Craig, D. P., and Dog§ett, G., J. Chem. Sue, 4189 (1983). (12) Kossel. W,, Ann. Phye., 49,229 (1916). (50) Mitchell, P. B,, and Parish, R. V., J. CHEM. EDUa, 46,811 (1969). (13) For a discussion of this approach aee &ailar* J. C, {Editor), "The Cheraistry of the (51) Pearson, W.B., AetaCryst., 17,9(19S4). Coordination Compounds," SeinhoM, New York, 1»5S, Chap1. 3 and Grinbetg, A. (52) Kjek&ns, &., Ada Chem. Scant!., 18,2379(1964). Ar "Introduction to the Chemistry of Complex Compounds, ' Add«on-WWey, (53) HuUiger, £\, and Mooser, B, Prog. Solid Stall Chem., 2,330 (19651. Reading, MA, 1M2, Chap. 7. {H) Htilliger, F., Struct. Banding iBerlin), i, S3 (196S). (14) Lewis, G. N., J. Amir. Chera. Scc.,3S, 762 (1916). (SB] Kjekshus, A., and Ratlte, T, Struct. Banding (Berlin], 19,46 (1974). 05) Lewis, G. N., J. Amer. Chan. SIK. , 36,1448 (19131. (5B) Schafer, H., Eigenmann, S., and Muller, W., Angeai. Chem. Int. Kit., 12,694 (1973], (16) Parson, A. L., Smithsonian Misc. Publ, 6S, 1 |I9I5). (51) Bent, H., Chem.fiEu.,61,276(1961). [171 Areem, W. C, J. Amer Chera. Sac, M, 1655 (1914). (58) Jensen, W. B.. Oe Educ. Quim., 3,210 (1978). In Spanish, English coBiM a™laWe upon (18) Kauffroaiw,H.,Physih.Z.,%311 (190S),alsoKaoffmann,H.,"Die Valeralehre,"Enke, request from Use au^ior. Stuttsatt. 1911, pp. 526-S46. (5B) Lewis, G. N., Chem. Reo., 1,231 (ISM}.

Chemistry Olympiad Mentor Applications Invited Applications are invited from chemistry teachers interested in serving as mentors for a group of American high school studeets entering the International Chemistry Olympiad (ICO) in Frankfurt, Germany, this summer. Duties involve helping plan and conduct a special study camp for student finalists to be held at a U.S. site in June, accompanying four student participants to the 30 June-9 . July ICO competition in Germany, and serving there as a member of the ICO jury. Applications aie invited from both experienced high school and university teachers of chemistry possessing strong background in the teaching of general chemistry and a broad, working knowledge of both theoretical and descriptive chemistry; experience in organic and analytical chemistry is also sought. Applicants must be prepared to commit full time to ICO activities from mid-June to mid-July this year, as well as a eomparabje time period in 1985. All mentor expenses and travel coats will be covered an4 an ho- norarium paid for the provision of ihe services described above. Interested individuals should apply by mailing a letter of application, resume, summary of relevant experiences, and the names and addresses of three references to Prof. Marjorie Gardner, Department of Chemistry, University of Maryland, College Park, MD 20742, (301) 454-3307. To guarantee consideration, applications should be received by April 30.

200 Journal of Chemical Education G. N. Lewis and the Chemical Bond > Linus Pauling Linus Pauling Institute of Science and Medicine 440 Page Mill Road, Palo Alto, CA 94306 S-.V

My first knowledge of Gilbert Newton Lewis came from cation of the new ideas, but not to the discovery of anything reading his paper on "The Atom and the Molecule," published significant. in 1916 in the Journal of the American Chemical Society (1). G. N. Lewis' 1916 paper introduced the theory of the shared During the year 1919-201 had a full-time job as instructor in electron pair chemical bond and revolutionized chemistry. quantitative analysis in the Oregon Agricultural College. At Comparison is often made of G, N. Lewis' paper and the paper the beginning of 19191 had not returned to the college, be- by W. Kossel (3) that was published in the same year. Kossel's cause of lack of money, and I was pleased when I had the op- paper (133 pages) was much longer than Lewis' (22 pages). portunity to teach the courses in quantitative analysis. My Even so, I think that Kossel's paper represented no significant office was in the chemistry library, where copies of the Journal contribution. Much of it is nonsense. He gave a long discussion of the American Chemical Society and of other journals were of electrostatic valence, but nothing about covalence, although available. My teaching load was very heavy, but I had some he suggested electronic structures for some molecules in which spare time to read tne journals, and when I ran across the 1919 the electrons were related to two nuclei. He mentioned the papers by Irving Langmuir (2) I read them with great interest, suggestion by Niels Bohr that in the hydrogen molecule two and also read G. N. Lewis' paper. I spoke on the subject of the electrons occupy the same circular orbit in a plane perpen- electronic theory of valence in the chemistry seminar that dicular to the roidline between the two nuclei, and he sug- year—chemistry seminars were rare, only about one each year. gested that in the nitrogen molecule the two nuclei, each with In 1922, when I received my degree of Bachelor of Science in a pair of K electrons, are held together by 10 electrons moving Chemical Engineering, I was offered and accepted an ap- in the same circular orbit in the plane midway between the pointment as teaching fellowin the California Institute of nuclei and in the plane perpendicular to the internuclear line. Technology. In September of that year, in the middle of the On the other hand, the two papers that Irving Langmuir train ride from Oregon to Pasadena, there was a stopover of published in the Journal of the American Chemical Society a few hours in the Bay area. I went to the chemistry building, in 1919, comprising 84 pages, contained many significant Gilman Hall, and found a young chemist, Roy Newton, at work in a laboratory on the first floor. He was good enough to talk to me for about half an hour about the work that he was doing and about the nature of graduate work in chemistry. I did not see I^ewis at that time, nor did I see any other person in the building—perhaps it was Saturday. VALENCE and I first met Lewis in 1924, when my wife and I went to Berkeley to see my old friend Lloyd Alexander Jeffress, who The Structure of Atoms and Molecules had got me interested in chemistry when we were both 13 years old. It is my recollection that I talked with Lewis about the work that I was doing on the determination of the structure of crystals by the X-ray diffraction method, and that I GILBKKT NKWTON l.KWJS c,iEUi$cm is TH got his permission to say in my application to the National OF C4UIMVLA Research Council for a fellowship to begin in July of 1925 that I would do the work in Berkeley. It turned out, however, that I did not go to Berkeley; instead I resigned the fellowship in the middle of the 1925-26 year, after having spent.the first few months in Pasadena, in order that I might go immediately to Europe on a Guggenheim fellowship. In 1928 Lewis spent a day or two in Pasadena. I learned about 50 years later that he had come to offer me a job, but American Qfcnliep! Sucicty that Arthur A. Noyes, the Chairman of the Division of Monograph Scries Chemistry and Chemical Engineering in the California In- stitute of Technology, had persuaded him not to do so. For five years, beginning in the spring of 1929,1 spent one or two months each year in Berkeley as visiting lecturer in physics and chemistry. During these extended visits to Berkeley I had the pleasure of talking with Lewis for many hours, in his office, his home, and his Marin County country place. My lectures were largely on new ideas about the 0 0 OK DEP ,i K T M E N T chemical bond and molecular structure based in part on the theory of quantum mechanics and in part on the empirical The CHEMICAL CATALOG COMPANY, analysis of the properties of substances. Lewis was, of course, I, EAST 14m SlBtlif, NEW YORK, V. !. A. intensely interested in the work. I am now, in retrospect, 1923 rather surprised that he and I did not write a paper together. So far as I can remember, our discussions led to some clarifi-

Volume 61 Number 3 March 1984 201 contributions and additions to the theory of the shared elec- atoms. Lewis also, after having placed the eight electrons of tron pair chemical bond. For some reason Lewis was an- what Langmuir called the octet (s2pe) at the comers of a cube, tagonistic to Langmuir, and in my opinion did not give him suggested that the electrons are in pairs at the corners of a proper credit In his 1923 book "Valence and the Structure of tetrahedron. In this way he could ascribe to the acetylene Atoms and Molecules" (4), Lewis mentions that after pub- molecule a structure with a triple bond, three shared electron lishing his 1916 paper he had intended at a later time to pairs lying at the corners of the common face of the two carbon present in a more detailed manner the various facts of chem- tetrahedra. Lewis discussed the partial ionic character of co- istry that made necessary his radical departures from the older valent bonds by writing that the electron pair is midway be- valence theory. He then continued (5) tween two identical atoms but may be shifted toward one or another of a pair of non-identical atoms. This plan, however, was interrupted by the exigencies of war, and in the meantime the task was performed, with far greater Langmuir (6) contributed the important idea of the elec- success than I could have achieved, by Dr. irviog Langmuir in a troneutrality principle—that atoms in a molecule hold elec- brilliant series of some twelve articles, and in a large number of trons to such an extent as to keep the electric charge of each lectures given in this country and abroad. It is largely through atom close to zero. In applying the electroneutrality principle these papers and addresses that the theory has received the wide be did not, however, make any correction for the shift of attention of scientists. electric charge resulting from partial ionic character. He It has been a cause of much satisfaction to me that in the course showed, using the electroneutrality principle, that a transition of this series of applications of the new theory, conducted with metal may have high covalence, such as 8 for nickel in nickel the greatest acumen, Dr. Langmuir has not been obliged to tetracarbonyl, to which he assigned a structure with a double change the theory which I advanced. Here and there he has been bond between the nickel atom and each of the carbon atoms tempted to regard certain rules or tendencies as more universal in of the carbonyl groups. He introduced the concept of iso- their scope than I considered them in my paper, or than I now sterisro, pointing out that molecules with an equal number of consider them, but these questions we shall have a later opportunity to discuss. The theory has been designated in some quarters nuclei and an equal number of total electrons in general have as the Lewis-Langmuir theory, which would imply some sort of very nearly the same structures. He concluded that CO2, N^O, collaboration. As a matter of fact Dr. Laiigmuir's work has been NCO~, NNN~, and other such molecules are linear. The lin- entirely independent, and such additions as he has made to what earity of the trinitride ion and the cyanate ion was shown later was stated or implied in my paper should be credited to him by Sterling Hendricks and me through our X-ray diffraction alone. studies of potassium trinitride, sodium trinitride, and sodium cyanate. Langmuir also reached the remarkable conclusion G. N, Lewis' main contribution to chemistry was the idea that the nitrous oxide molecule has the linear structure NNO that the chemical bond (named the covalent bond by Lang- rather than NON. In his discussion of the Heusier alloys, muir) is at all times a pair of electrons held jointly between two which contain manganese, copper, and small amounts of arsenic, aluminum, or other elements and are ferromagntic, he stated that "Copper has too many electrons. It gives one to manganese to make the atom like the iron atom." This statement shows remarkable insight. THE GEOHCE K1SHER BAKEH N0N.RES1UF.M LECTURESHIP !N CHEMISTKY Langmuir, however, was wrong in some of his ideas. He re- AT COIt NELL UMVERS1TV garded quartz as containing SiOa molecules similar to the molecules of carbon dioxide, and said that the hardness is the result of the Seating of residual silicon-silicon forces. Lewis, in fact, had made a similar suggestion in his 1916 paper. Only THE NATURE in 1923 did Lewis reab'ze that the silicon atoms are held together by bridging oxygen atoms. OF THE CHEMICAL BOND Langmuir also assigned to the P4 molecule a ring structure AND THE STRUCTURE OF MOLECULES containing alternating single and double bonds. He overlooked AND CRYSTALS the possibility of a tetrahedron with only single bonds between the phosphorus atoms. Similarly, his structure for P4O8 involves a square of phosphorus atoms held together by single An Introduction lei Modern Structural Chemisli) bonds, with two oxygens attached to each of two phosphorus atoms and one to each of the other two—not a very sensible n structure. LINUS PAULING In his 1923 book Lewis discussed early suggestions about Profasot of OitKistr, in A* the electronic structure of molecules that had been made by California Inatiiat* of TK*molo*y Kossel, Stark, and others, especially A. L. Parson, a student BbCONQ EDITION who in 1915 published an interesting paper entitled "A Magneton Theory of the Structure of the Atom." Parson considered the electron as a rotating ring of negative electricity that accordingly possessed a magnetic moment and could be called a magneton. Lewis says that it was he who suggested to Parson that the magnitude of the magnetic moment to be assigned to such a spinning electron was constant, whereas Parson had considered it to be variable. Parson and Lewis thus anticipated by 25 years the discovery that the electron has a ITHACA, NEW YORK spin and a magnetic moment. Lewis, however, then rejected CORNELL UNIVERSITY pit ESS the idea, writing, "This idea has not proved fruitful, and it LONDON; HUMPHREY MSLfORD seems unlikely, although perhaps not impossible, that an OXFORD UNIVERSITY PRESS 1945 electron possesses any magnetic properties except when it is a part of an atom or a molecule." Lewis felt an indebtedness to Werner, writing that "His 'Neuere Anschauungen auf den Gebiete der anorganischen Chemie' (1905) marked a new epoch in chemistry; and in at-

202 Journal of Chemical Education tempting to clarify the fundamental ideas of valence, there covalent bond, because if it were less stable the molecule would ia no work to which I feel so much indebtedness as to this of have a structure involving pure covalent bonds between the Werner's." However, in his discussion in 1923 of the types of unlike atoms. The necessity for making a correction in the coordination postulated by Werner (octahedral, tetrahedrai, heats of formation of compounds involving reaction of diox- square planar), Lewis did not make any mention of the results ygen or dinitrogen {Os or Ng) with single-bonded elements to of the study of crystals containing these coordination com- form single-bonded products is a complication, but chemists plexes that had been published during the preceding two years knew even before quantum mechanics that the bonds in these by Roscoe G. Dickinson and R. W. G. Wyckoff, who had ver- molecules are not single bonds and that the molecules might ified the octahedral arrangement in crystals such as KgSnC^ have greater stability than single-bonded molecules have. and K2PtCls, the square arrangement in K2PdCI4 and Langmuir formulated the electroneutrality principle, but did KaPtCLi, and the tetrahedrai arrangement in K2Zn{CN)4 and not make much use of it, and Lewis ignored it The reason may K2Cd(CN)4. No X-ray work was being done at that time in the well be that the principle does not work very well unless the College of Chemistry at Berkeley, and Lewis seems not to have partial ionic character of bonds is taken into account, and until been following the developments in X-ray crystallography. the eleetronegativity scale was developed it was not possible to discuss the partial ionic character in a satisfactorily quan- G. N. Lewis was remarkable in his originality. I was much titative way. Moreover, Lewis did not make use of the theory impressed in the early 192O's when I read his paper an- of resonance, which had not yet been formulated in 1923 but nouncing the discovery of the O4 molecule. He had asked why which might have been proposed, as was done by Robert the paramagnetism of oxygen dissolved in liquid nitrogen Robinson and C. K. Ingold in 1926, in the theory that Ingold decreased as the concentration of the oxygen increased. He called mesomerism. Lewis in 1923 expressed some concern was able to show that he could account for the experimental that a structure of the carbonate ion in which one oxygen atom values of the magnetic susceptibility of solutions of oxygen is held by a double bond and two by single bonds seems, as had in nitrogen by the assumption that there is an equilibrium been stated by Latimer and Rodebush (in Berkeley) three between paramagnetic molecules of dioxygen and the dia- years before (7), to be in contradiction with the apparent magnetie molecules of tetraoxygen, O4. From the values of the trigona! symmetry of the ion in calcite as shown by X-ray paramagnetic susceptibility he was able to evaluate the diffraction. The idea that the double bond resonates among standard Gibbs free energy change and the enthalpy change the three positions apparently did not develop in Lewis' mind for the reaction. at that time. Aa I think about the history of the chemical bond, I ask myself why some of the discoveries that were made in the Gilbert Newton Lewis showed himself to be one of the great quantum-mechanical era of the 1930's were not discovered chemists of the 20th century through his work in chemical earlier. The electron egativity scale of the elements is an ex- thermodynamics and other fields, as well as through his for- ample. It was formulated in 1933 through the analysis of the mulation of the basic principle of the chemical bond—the idea decrease in enthalpy accompanying reactions in which single that the chemical bond consists of a pair of electrons held bonds between like atoms are converted to single bonds be- jointly by two atoms. l tween unlike atoms, such as kH2 + W^h -* HC1. The basic idea, attributed to quantum mechanics in 1933, is that the Literature Cited partial ionic character of a bond makes it more stable, with (1) Lewis, G. H, J. Amer. Chem. Soc, 88,762(1916!. lower energy, than a pure covalent bond between the unlike (2) I-anginuir, I.. J. Amer. Chem. SBC.,U, 868, 1543 (1919). atoms. This idea is, in a sense, not a quantum mechanical idea; (3) Koesal, VS., Arm. Pliysik. 49,229 (IBIS). we might well have concluded before quantum mechanics was (4! Lems, G. N, "Valence and the Structure of Atomaand Molecules," The Chomirai Catalog Company, Inc., New York, i»23. developed that if the actual bond is a covalent bond with (5} Referent (4), p. 87. partial ionic character it must be more stable than the pure (6) Lanjitnuit, I., Science, 54.59 (1921). (71 Latimer, W. M., and Rodebush, W. H.. J. Amer. Chum. Sor.,12,1419 (1920}.

Publications on Environmental Analysis and Ground Water Available from ACS "Principles of Environmental Analysis," published in the December 1983 issue of Analytical Chemistry, is now available as a separate brochure from the American Chemical Society. Developed hy the ACS Committee on Environmental Im- provement's {CEI) Subcommittee on Environmental Monitoring and Analysis, this publication identifies elements needed to obtain reiiable data as well as factors tiiat have been shown to produce unreliable measurements. Its intent is to aid in the evaluation of the many options available in designing and conducting analytical measurements of environmental samples and in the intelligent choice of those that will meet the requirements of the situation at hand. These situations range from semi-quantitative screening analyses to those involving strict quality assurance programs intended to document the accuracy of data for regulatory enforcement or legal purposes. Discussion focuses on planning, quality assurance, and quality control, verification and validation, precision and accuracy, sampling, measurements, and documentation and reporting. While the "Principles" brochure is meant as an aid to those working in the field, the ACS has also produced the third in its series of informational pamphlets that discuss science-related regulatory issues and that are geared to the general public. The "Ground Water Information Pamphlet," also written under the auspices of CEI, focuses on what ground water is, where it occurs, and its volume and Quality. Due to the extensive use of ground water, the pamphlet alao outlines the scientific aspects of ground-water depletion and degradation. It is not meant to formulate answers to the complex questions inherent in ground-water management. It does, however, present fundamental concepts concerning the chemistry of ground water and begins to huild a basis from which citizens can evaluate information about ground-water problems, construct plans of action, and gauge the implications of that action. The pamphlet is written in clear, concise fanguage that educators will find useful in the classroom for high school and college students alike. Single copies of the pamphlets are free. Multiple orders can also be accommodated. To obtain a copy, call 202/872-8725 or write to Ms. Jean Parr, Department of Public Affairs, American Chemical Society, 1155 16th Street, NW, Washington, D.C. 20036.

Volume 61 Number 3 March 1984 203 The Triplet State An Example of G. N. Lewis' Research Style

Michael Kasha Department of Chemistry and Institute of Molecular Biophysics Florida State University, Tallahassee, FL 32306

In the last two years of his life, between the ages of 68 and Confusion concerning the three items just mentioned 70, Gilbert R Lewis brought to fruition and focus his long- abounds in the literature before 1944 and had a considerable germinating ideas on the triplet states of molecules. I had the momentum afterward. We shall examine some of the key great fortune to be his collaborator in this research. These contributions to the general background in the various au- researches, published in two papers in the Journal of the thors' own words and diagrams to indicate the gradually de- American Chemical Society in 1944 and 1945, were destined veloping tapestry of uncertainty against which the work that to have a profound effect on the course of the subsequent Lewis and I published in 1944 was hung, development of molecular spectroscopy and photochemistry. However, the influence was not instantaneous, since more G. N. Lewis on Triplet Ethytene and Singlet Oxygen than a decade was required to overcome the negative pressure Lewis began to think about electron arrangements in eth- of prestigious opponents (Franck, Teller, Livingston, Rabi- ylene and molecular oxygen on the basis of electron pairing nowitch) and to unravel the complexities and misunder- long before any other researcher, as a consequence of his early standing of earlier research, electronic structure models. Because ethylene triplet and In this presentation I shal! examine in retrospect the oxygen molecule singlet states are so intertwined with general background of ideas against which Lewis' last researches were thoughts about the triplet states of molecules and their done, report my personal interactions with him in the hope quenching (involving singlet molecular oxygen), it is of interest of revealing his personality and joi de vivre, reflect on some to cite Lewis' developing ideas on these species. general observations and views of Lewis on the conduct of In his 1916 paper, "The Atom and the Moiecule" (2), Lewis scientific research, give an analysis of a unique habit of Lewis' states hi considering interactions of oxygen and ethylene writing of research previews, and indicate through his personal research memoranda to me his intensity of research These two forms of oxygen (which of course may merge into one interest and activity in the last years of his life. another by continuous graduations) can be represented as

Historical Perspective on Molecular Triplet States :O::O: and :o:o: A spectroscopist today is easily baffled by any indication that observing triplet states of organic molecules constitutes and the two forms of ethylene as in any way a difficulty or a mystery or puzzle, The evolution H H H H of the observations and understanding of polyatomic molecule singlet-triplet transitions took a quite different path than the :H:C::C;H and H:C:O:H development of atomic and diatomic spectroscopy. The knowledge of the latter subjects led Sponer and Teller (1941) These are clear Lewis electron-dot representations of sin- (J) to the view glet and triplet arrays for the molecules. A later statement (1924) clarifies the issue of their representing discrete As in the case of atoms we have, in first approximation, the se- states lection rule that oniy states of the same multiplicity combine with each other. Intercombinations occur with appreciable inten- The enormous difference in magnetic properties between the sity only if the molecule contains some heavier atoms. oxygen molecule and other molecules to which we attribute double bonds seems to support the idea that the change from a non- Such a background sets the stage for the expectation that in magnetic to a magnetic molecule is not a gradual process, but that molecules with low Z (or "light") atoms, such as C, N, 0, and the molecule must possess at least one unit of magnetic moment H, no singlet •** triplet transitions are to be observed. Here we or no magnetic moment at all. can state at once the origins of the dilemma This paper (3) is titled "The Magnetochemical Theory" (1) Radiationless transitions are essentially absent in atoms and and was the first to present in effect an electron spin restric- diatomic molecules and are known today to be simply the tion on molecular interaction, a topic very much alive today. common phenomenon in polyatomic molecules; thus, in Lewis did not speculate on the spectroscopic implications of polyatomics a prevalent mode of excitation of highly for- his normal and "diradical" configurations. bidden state (e.g., triplets) is abundantly available. (2) The terms "high intensity" and "high transition probability" H. Kautsky: Sensltlzation Mechanisms by Molecular carry an implication of a direct correlation. But "intensity" Metastable States and by Singlet Oxygen of emission is measured by quantum yield, so that "forbidden" triplet state of low transition probability (measured The German photochemist Kautsky wrote a long series of by long mean lifetime) can be observed with high "intensity" qualitative papers which reported ingenious experiments (meaured by high quantum yield) in polyatomic mole- describing metastable excited states involved in photosensi- cuies. tization processes. (3) The original observations on phosphorescence emission of Metastable states of molecules were cited in one series of organic molecules were made for rigid glass solutions (organic papers (4) in which Kautsky, et si. demonstrated effectively so(vent mixtures frozen to glass at 90 K or 77 K). Most of the that sensttization of molecules (energy transfer) by dyes is early interpreters of the phosphorescence phenomena of organic molecules were preoccupied with "clamping of un- facilitated by aggregation of the dye molecules. Kautsky usual conformations (tautomers) by the rigid glass me- mistakenly thought that aggregation was a necessary pre- dium"—which in those days seemed so essential to the ob- condition for metastable state excitation, failing to distinguish servation of the long-lived luminescence. between intrinsic metastable state excitation and induced

204 Journal of Chemical Education metastable state excitation. The nature of the metastable state is labelled I in Figure 1. His states are labelled N, normal; F, of dyes adduced by Kautsky was not alluded to. His diffuse fluorescent; M, metastable. Jablonski could never accept the writings, merging many discrete phenomena and interpreta- M state as a triplet state, and even as late as 1958 (13) he still tions, had no diagrams or quantitative data. tried to account for this state as a singlet excited state of low Singlet molecular oxygen was cited by Kautsky et al. (5) probability! Key quotations from his first papers (12) clearly in another series of papers in which the excited singlet mo- reveal the concepts of {1) an intrinsic electronic metastabie lecular oxygen species, generated by energy transfer from state, and (2) attempts to interpret the forfaiddeness of tran- metastable states of dyes, were considered the active inter- sitions by multipole or other than singlet-triplet mecha- mediate in photooxidation. This interpretation was lost until nisms: its recent belated and fiery revival {6-8). We assume in the case that an "energetically isolated" dye- Singlet-Triplet Spectrum of Ethylene molecule k phosphorescence-capable, then there must exist in this molecule at least one metaatable level. In an early paper (9) C. P. Snow and C. B, Alsopp presented a seemingly authentic weak absorption spectrum of various The transition between the ground level N and the metaslable ethylenes, interpreted as representing the singlet-triplet ab- ievel M can occur only with small probability (as for example by forced dipole radiation or quadrupole radiation). If there exists sorption. This observation escaped particular attention at the somewhat above the level M and unstable level F, which com- time and proved to be ten times too intense to be genuine {10). bines with the ground Jevel N {only this case will be discussed in The singlet-triplet absorption was found by C, Reid in 1950 detail here), then wii! the level M in greater part be reached by a {11), the extraordinarily weak absorption observed from detour through F. 31,000 to 37,000 cm"1 at 120 K requiring a 1.4-m path of liquid ethylene. Jablonski was entirely concerned with the mechanism of Robert Mulliken visited Berkeley sometime in 1942 and photolitrriinescence processes of dyes, stressing a kinetic gave a talk about molecular orbitals of ethylene. G. N. Lewis derivation of the thermal activation of the F (fluorescent) level told his research student Jacob BigeleisenJ afterwards, "You from the M (metastable) level. It could be said that his know, those triplet states that Mulliken was talking about in treatment would not apply to polyatomic (non-dye) molecules ethySene are probably the phosphorescent state." So Lewis in general, since the large excited singlet-triplet energy gap had triplet states of organic molecules like ethylene very much would preclude Jablonski's kinetic treatment, aside from his on his mind. failure to accept the triplet designation of the metastable state of molecules. Later use of the "Jablonski Diagram" fails to Jablonski Diagram for the Lowest Metastable State of Dyes recognize the limitations of his interpretations. Jablonski, the Polish theoretical physicist, published an Franck and Livingston Tautomeric Metastable Model interpretation (12) of some of the Kautsky observations on the metastable states of dyes and other known physicai ob- The use of glassy media and adsorbed states in the study servations on dye-phosphors (dye molecules dissolved in sugar of the phosphorescence of dye molecules was a major preoc- glasses and boric acid glasses). He ignored the aggregation phenomena which confused Kautsky and treated only the intrinsic properties of dye molecules. A replica of his diagram 1 Personal communication.

J F 120 - ___r —._ c' d - ==J -"-i— "~ "~"~"^^ k M i i ] i e a b \9 N' i f 1 1 1 i i 1 i i 1 i 1 • • N I :^ 1 1 1 0 11 1 * II Figure 1. Various enetgy diagrams tor dye molecules. I. Jabfonsk! diagram lor the lowest meiastabte state of dyas (12).

II. Franck and Livingston tautomeric metastable model (14).

HI. Lewis, Lipkin, and Magel's energy diagram of Ruoresceln in boric acid (17).

IV. Lewis and Kasha's energy level diagram for add tluorescein (19).

MONOMER DIMER V, Kasha and Mcftae's energy level diagram for a V dye molecule versus s dye-dimer (?2|.

Volume 61 Number 3 March 1984 205 cupation of all authors writing on the subject before 1944. Several suggestions have been so far advanced as to the nature Thus in 1941 James Franck and Robert Livingston (14) pre- of this metastable state in dyes, uiz. sented the idea of a tautomer of the normal molecule rigidly (a) a highly endothermic and reactive dye tautomer, formed clamped by the environmental medium: by the transposition of a "labile" hydrogen atom; (b> a geometrical isomer or distorted dye moiecuie formed as a Many of the apparently conflicting facts of the photochemistry result of a strong vibration, imparted to tiie molecule in its radia- as weii as of the phosphorescence and the fluorescencequenchin g tionless transit to the ground state, the abnormal configuration of dyes can he given a rational and unified interpretation if it is being stabilized by the environment, acting like "jsws"; assumed that an electronically excited dye molecule can go over, (c> an electromer of the dye, in particular, a triplet state or by a process of interne! conversion, to the electronic ground state biradical, from which the transition to the ground levei is being of a reactive energy rich tautomer. prohibited by selection rules. The Franck and Livingston diagram is reproduced as II in Terenin rules out tautomerism on the basis of energy con- figure 1. A potential curve model later given by Forster (15) sideration and then states for the Pranck-Livingston model suggests the seemingiy un- It is, in our opinion, the alternative, mentioned under

206 Journal of Chemical Education showed (20) that by dipole-dipole coupling, of parallel-tran- that in addition to a strong absorption band expected in the sition-momeat dimers a forbidden (metastabte) singlet-state visible region, I had found an unexpected characteristic strong for the dimer should arise. He assumed this to be the meta- band in the middle of the neaT infrared for each dye I had stable level ascribed by Kautsky to both phosphorescence and studied. photosensitization (our 1944 paper was still not available to Lewis began to speculate: what could this new electronic Forster because of World War II dislocations). Forster later band be? He soon had an explanation. The poiyeyelie quinone (21) adopted our triplet state model for the metastable dyes which we were studying could be described as large pla- state. nar oval or round molecules. Lewis thought: "Could it be that McRae and I (22, 23), pursuing Szent-Gyorgyi's experi- we have found the low-energy circular osciilation of electrons, ments on dye phosphorescence enhancement in frozen water in addition to the higher energy x and y Cartesian oscillation versus frozen alcohol glass, approached the dye-dimerization of the previous type?" The test was then to study as many problem by molecular exciton theory. Our diagram is given linear absorbing moiecules as could be found: a carotene or in Figure 1 as V, showing that for a dye molecule singlet-singlet lycopene. Special samples were obtained from Professor fluorescence dominates the luminescence, whereas in the Zechmetster of Cal Tech. While waiting a week or two, I added dye-dimer (in water) the metastable singlet exciton state ra- to our list of new spectra. diationlessly goes over completely to the triplet state, giving The absorption curves for the "linear" electronic systems phosphorescence dominance in the dimer. Thus, we effectively (carotenes) revealed once again strong electronic bands in the explained the Kautsky dilemma, and in effect, combined near infrared region, characteristically mimicking the visible Forster's two diagrams into one. absorption bands of the molecule, as in previous "round molecule" cases. Each molecule showed a typical vibrational 2 Research with G. N. Lswte envelope, band width, and spectral position, analogous to its strong characteristic visible absorption. First Contacts When Lewis saw that the Beekman Spectrophotometer When I came to Berkeley in February, 1943, G. N. Lewis was gave these results on linear molecules as well, he said, 68 years old and had recently stepped aside as dean of the College of Chemistry; I had just turned 22.1 had come as a "Take Me To Your Spectrophotometer!" graduate student determined to work with Lewis, as he was Lewis asked me to explain the various components and their certainly the best known physical chemistry professor then operation, He had me unscrew the phototube and cell com- at the University of California at Berkeley. The chemistry partments, exposing the exit slit of the spectrometer. graduate students were required to select a professor before Then he said, the end of their first semester and to commence research in that term. I went through the obligatory list of interviews in "Set the monochromalor dial for 550 rojU," pro forma routine, saving Lewis for the last. My first hour with and poised himself in line with the exit beam. Lewis was impressive. I must have appeared nervous, for He said, Lewis said, "Now don't think I'm going to embarrass you by asking you a lot of detailed questions about physical chemis- "I see GHEEN." try. I would just like to tell you about some of the interesting Then, research which we have been thinking about recently," "Set the monoehromator for 600." Lewis then proceeded to talk with excitement about the He said, phosphorescence studies done with David Lipkin and Theo- dore Magel and the absorption and photochemical studies just "I see YELLOW." then being completed with Jacob Bigeleiseri, who overlapped Then, with me for the month of May of 1943. Lewis and Calvin had developed earlier a semi-classical theory of light absorption "Set the monochromator for 700." in dye molecules, and Lewis and Bigeieisen had done both He said, some elegant polarization studies of #-band andy-band mo- "1 see RED." lecular coordinate resolution of the electronic transitions as well as related photochemical studies. Then, Lewis had his mind on a new class of dye molecules, the "Now, set the monoehromator for 1,000 nt/i." large poiyeyelie quinones (like pyranthrone, violanthrone), With excitement, and suggested that I measure their absorption spectra carefuily. Bigeieisen gave me a master's introduction to what was "Aha! I am the first man to see the INFRARED. And it is probably the Chemistry Department's sole electronic in- GREEN!" strument, the battery-operated Beekman DU Spectropho- Lewis had suspected that the monoehromator was misbe- tometer, housed in the Old Chemistry Building. Having having, and we quickly saw that the whole of the visible learned its operation (and idiosyncrasies), I proceeded to spectrum could be seen on this instrument by scanning the measure absorption curves of my dyes. The instrument scale near infrared from 750 to 2,000 m&. Thus, any visible dye started at 2000 nm (then mfi!), and so did my readings. would show an illusory absorption spectrum on the background of this scattered light, apparently reflected off the An Intensive Month of Spectrophotometry instrument wall. There are probably some false curves in the I measured several curves one week from 2000 nm (hardly earlier literature based on this error. Lewis taught me to be knowing that I was in a forbidden region of the infrared), to wary of instrumental performance. 200 nm, the other limit of the instrument. No one in the laboratory had done this before (as all sensible operators started Phosphorescence and the Triplet State at 750 nm—the visible limit), and I-ewis was astonished to see, Lewis held a daily research conference with me at 11:00 a.m., usually lasting an hour. Each session launched major plans to be carried out that very afternoon and evening. By 2 This and the sections of this report designated with an asterisk are the end of such an hour, a whole strategy for the day was taken from Kasha, M., "Four Great Personalities of Science—G. N. mapped out. No apparatus was too complicated to be assem- Lewis, J. Franck, R. S. Mufliksn, and A. Szent-Gyorgyi," Scientific Es- bled that day, at least in a preliminary form. Of course, I had says, Tokyo Science University Lectures, 1979, to be published. an enormous advantage over other graduate students since

Volume 61 Number 3 March 1984 207 Lewis could call on any and all shop men for instant ser- molecular correlation, In atomic spectroscopy and diatomic vice. spectroscopy there was no difficulty with assigning multi- After the month's debacle with the dye spectra, Lewis and plicities and observing forbidden transitions. I believe that I both wanted a refreshing change. I suggested phosphores- one of the retardations on the understanding of polyatomic cence had many puzzles to resolve. Lewis agreed, and said, triplet states was the fact that the techniques used for obser- "Have the shop build a phosphoroscope." Lewis then left for vation of molecular phosphorescence, solid solutions in rigid a month's vacation. It was the first day of June 1943, and Bi- glass matrices, impinged on the doped-inorganic-impurity geleisen had two or three days left in Berkeley. "Jake, what phosphors, and the suspicion carried over that the strange is a phosphoroscope? " I asked. He was furious that I had not rigid-glass media those Berkeley chemists were using could used the library. "Look it up!" was his answer. I studied the involve analogous solid state phenomena. It is hard to believe idea of the Becquerel phosphoroscope, and designed one with today .the general negativism and even hostility which greeted parallel discs and had it built the nest day. Bigeleisen's parting the presentation of this work. It took 10 years to overcome suggestion to my question "What shall I study?" was: "Try early prejudices before the phosphorescence of molecules carbazole, it seems to have a very long-lived blue-violet assigned as the lowest triplet — singlet transition became phosphorescence." This suggestion proved to be worth its universally accepted as it is today. Certainly the Lewis and weight in gold. In the Lewis inner laboratory, where the old Kasha study showed that phosphorescence was an intrinsic brass-tube and mahogany-wood-boxed Medium Hilger Quartz molecular characteristic, independent of the medium or sol- Spectrograph was housed, was a score of large desiccators vent used. Probably, aside from the novelty of the apectro- containing boric acid and dextrose glass phosphor slabs made scopic technique, the lack of comprehension of the rote of with various dyes BB solutes {from the 1941 work of Lewis, radiationless processes in polyatomic molecules was the other Lipkin, and Magel). All of these dye "phosphors" exhibited source of diffidence. broad-structureless phorphorescence. If I had also studied only dyes, our work may never have developed the direction In the second year of my work with Lewis, World War II was and significance that it did subsequently. in its intensive final stages, and I was permitted to remain in Berkeley only if I joined a wartime research project. I easily The carbazole molecule spectrum was astonishing, even to made the timely decision to take on the heavy extra burden me as a beginning spectroscopist. The spectrum consisted of in order to continue with Lewis. So in this second year, Lewis numerous marvelously detailed "sharp" bands. I don't know and I saw each other each evening and Saturdays, and fre- how I contained my excitement. I probably showed my spec- quently on Sundays. We averaged six hours a day together in trographic plates to everyone in the building. Jacob Bigeleisen our whole period of two and one-half years of contact. Our first had left before I got a spectrum. Lewis was away for a month. paper was written in July and August 1944 in the evening I was the only graduate student in his laboratory. Having just hours between 7 and 11 p.m. Meanwhile, our attention had finished Harvey White's Atomic Spectra and Structure course turned to singlet-triplet absorption studies, and a paper was in the Physics Department, the excitement of spectroscopy published in June 1945 entitled "Phosphorescence in Fluid was in me. That month I ran through several dozen molecular Media and the Reverse Process of Singlet-Triplet Absorption" samples: naphthalene, benzophenone, anthraquinone, benz- (24). In February 1945 i had completed my PhD degree on the aldehyde, nitronaphthalene, etc. Every molecule showed basis of these two researches. characteristicaily "sharp" banded structure, All of these were studied in EPA glass at 90 K (we had only liquid air as a G. N. Lewis Daily Research Memoranda coolant). The bands observed, were very numerous and highly structured compared with any of the dye spectra which had In June 1943 the research on phosphorescence of organic been obtained in the laboratory before. molecules in low-temperature rigid glass solvents had started in earnest. It may not be out of place to give some indications Lewis was delighted and excited by the result when he re- of the intensity of this research and the pressures which pro- turned. Our work was now turned fully to a broad exploration duced such a concentrated effort. The world was at war and of the phosphorescence of organic aromatic molecules in rigid academic research in universities was under severe restriction glass solution at low temperature. My phosphoroscope, vac- from every side. In 1943 I was still eligible for deferment from uum sublimers, and vacuum stills ran 24 hours a day for the Army conscription since I was a teaching assistant in general year. At the end of that first summer I was allowed to give a chemistry, teaching especially the large groups of Navy research seminar on the preliminary observations. Admit- Medical Corps students. There was a realization that all of the tedly, the presentation was somewhat repetitive in that I tried few graduate students of chemistry would rather soon take up to show how virtually every moieeule we studied showed a war work of one kind or another. Perhaps that contributed to characteristic low-temperature phosphorescence—especially the pace of work as much as anything. if the molecules were non-fluorescent. The rest of that year In interviewing me a few months earlier, Lewis gave a fair, was spent in an intensive study of the phosphorescence of over thoughtful appraisal of our future relationship, He said, "You 100 different molecules. don't know me, and t don't know you. Let us say you start an In July of 1944 our work was ready to be written up. The apprenticeship, and in a month or so, for any reason, if you procedure used in writing this long paper is worth record- don't like working with me, or 1 don't like working with ing—as it at first startled me. Lewis seated me comfortably you—then we can part freely without friction on either side." in the wide-armed, high-backed wicker chair which greeted We immediately worked so well together that the appren- all his guests, with pad and paper in my hand, and dictated ticeship was never mentioned again. the paper in perfect flowing English from beginning to end! Lewis had asked no questions about my background, but I was allowed little interruptions here and there, with an oc- two of my past experiences prepared me especially wen for the casional slight change of perspective, but on the whole that intensive period ahead. In my teen years I was in effect the first paper (entitled "Phosphorescence and the Triplet State apprentice of a Pennsylvania carpenter and cabinet maker of (19)) was already in Lewis' mind. How could he do it? I won- unusual skiil. I was his "man Friday." Every evening I was his dered. Then I realized that everything had been discussed instant assistant, knowing every tool, knowing every piece of endlessly in the laboratory, and finally, as Lewis puffed his stock in his shop. I could tell by his glance what he wanted cigar and paced up and down Gilman HalJ and across campus, next, hardly more than a nod being necessary. In working with the perfect phrasing of each thought was developed. And when Lewis,! developed the same relationship. In our many hours we sat down together, he was ready! together each afternoon, I knew his favorite optical filters, his It is odd in retrospect that "Phosphorescence and the favorite optical accessories. Our work went swimmingly, and Triplet State" shouid have to come as late in 1944 as a secure we had much good humor between us.

208 Journal of Chemical Education complete set. They are scribbed in soft pencil on yellow paper. Unfortunately, most are undated, but the research they describe allows their sequential arrangement. The few that I dated at the moment are indicated. They tell a fascinating story of Lewis' intense interest in our rapidly evolving project. Our first molecule of special interest was carbazole because of its "sharp" bands. By the strangest coincidence the two strongest vibrational peaks of the phosphorescence of carbazole coincided almost exactly with the 4047 and 4358 A lines of our 1-kW AH6 high-pressure, mercury-exciting light. Lewis at first thought we had some super-enhanced Raman scat- tering. In a rather dramatic experiment using a powerful Mg-cored carbon arc, with the beam transported across 5m of laboratory and with our phosphoroscope flashing (everyone in Gilman came to see the big experiment), we quickly found that even with farther UV excitation the same carbazole phosphorescence bands resulted. We did every kind of experiment to prove that our previously unobserved carbazole bands were unique, real, and characteristic. Lewis left me the following message.

Figure 2. Lewis at vacuum line in laboratory on the third lloor of Gliman Hall at the time tn 1940's when he was conducting research on color and the triplet state.

My second experience of which Lewis had no inkling was my two and one-half years employment at the Merck Research Laboratories in Rahway, N. J. While going to The Cooper Union Night School of Engineering in New York City, I worked first with the famous chemist Karl Folkers on eryth- rina alkaloid extraction from poison heans, and fractionation of the alkaloid components. My triumph was the separation of 1.5 g of crude alkaloid into 14 pure alkaloid components by microcrystallization techniques. In my second year I did mi- / think the most important next thing is to get the fluorescence crobioassays for the entire research laboratory, whose staff of carbazole in liquid air-—it may take a very long exposure but the was in hot pursuit of a then unknown vitamin, pantothenic overexposure of the phosphorescence is too far away to bother. acid. I worked on every aspect of this {at the age of 18-19): GNL pilot plant isolation, synthesis of intermediates, and the daily bioassays (Lactobadllus casei growth curves). The excitement We then began systematically to study all sorts of typical of pursuing an elusive research goal, and the pressure of the organic structures: responsibility of the daily bioassay coupled with night school engineering studies tuned my working habits to the intense regime tacitly demanded by Lewis.

Our daily routine started when Lewis appeared in his office at 11 a.m. for our 1-hr lecture-discussion at the blackboard. The afternoon's work now outlined, he went to the Faculty Club, with the expectation that upon his return at 2 p.m. the new experiments would be ready. Quite often this meant a major feat of glassblowing, metalwork, carpentry, electrical wiring—especially if apparatus had to be moved into the building corridor as it occasionally was. Several shop people After dinner the whole still should be at room temperature would be working furiously to get things ready. From 2 until Remove inner part—scrape off what you want of the naphtha- 5 or 6 p.m. wild, rough experiments would be done. (Figure 2 lene—and replace inner part in still shows Lewis doing vacuum line work from this period.) Then GNL Lewis would take his departure with the comments: "Very Good! Very Interesting! Just polish up the measurements a We began to recognize quickly that we could tell purity of bit and well study them in the morning," After a quick dinner our compounds from the simplicity and beauty of the phos- I would return to the lab and frequently work until midnight phorescence bands. Naphthalene usually showed a ghost on the expected polishing of the afternoon's work. In the spectrum to higher frequency, which I could only get rid of by morning, with a lot of neat curves, spectral plates, tables of crystallization from ethanol, whereas sublimation seemed to data laid before him, Lewis would say: "Well, we did very wel! concentrate the impurity, I later diagnosed the volatile im- yesterday afternoon, didn't we?!" purity to be benzothiophene. Lewis would scribble notes to me if we somehow missed The very large polycyelic quinone vat dyes were still on each other. I saved these in a file so that I would not forget to Lewis' mind, but running concentrated H2SO4 as a glass so- carry out any requests. Then later 1 realized they could be of lution of the polycyelic quinones at 90 K gave very complex historical interest, so I still possess what I recall to be the bands.

Volume 61 Number 3 March 1984 209 12/27/43 •*,r / think this is the filter we want—511. with a yellow filter on the other side. C11SO4 should also be used. Perhaps, uihen I come in tomorrow we will try the effect of O3. We .- A'* - ' shall want fluoresein and eosin in slightly alkaline alcohol We kept up the oxygen quenching experiments; we continued extending our repertoire of spectral types of phosphorescence.

7/6/43 When you do the vat dyes in Ha SO41 suppose you will use the 9000 A plates if there is phosphorescence GNL *>••/. ,-<•. Lewis got very interested in the vibrational structure and bad Linus Pauling pay a visit. Pauling then wrote a communication for the Journal of the American Chemical Society 12/28/43 at Lewis' suggestion using our data. My experiments were interesting, and I want to try them all again

in your presence•

In the meantime start subliming in vacua a little dinitro~di-

phenyl

GNL

ft We spent quite a bit of time looking at simple molecules, discussing literature ideas on triplet ethylene especially. The

ethylene experiment was done badly, since we did not check

if any light was absorbed. The high-pressure arc probably was

unsuitable as an excitation source. ( HI i htfi 'llrfir~; * • utui ••tij ii--hi'>? ,t-hn,i, ,i-l,(

" „,. P~

Regrease main stopcock on vac line. Tried two tubes of C^H^—no phosph. to speak of. This tube is SO% Brilliant green phosph! one of the shortest half lives we have seen. No good bands I think I would like one photograph of 2-nitro-fluoreneWe were aware of the wavelength problem, but had no better GNL luck with the next larger polyene.

Lewis was toying with ideas of O2 perturbation, but we did not succeed in accomplishing any definitive work on this, since when our solvents were frozen in glass, the perturbation effects V " » were negated. (This dilemma plagued me for several years until I thought of the singlet-triplet absorption experiment Butadiene—no phosph.! in ethyl iodide solvents.) The data of this memorandum re- minds me that I had Christmas day off from research that Polyenes turned out to be elusive for a long time afterward. month, but it was very lonely because my family was 3000 In about February 1.944, a big personal decision loomed: join miles away and my brother was fighting tanks in Europe. the U. S. Army, go to Central America on a Signal Corps project, or join the Manhattan District (Plutonium Project)

in Berkeley. Lewis expressed his hope that I would do the last,

/•- - and 1 did without bestiation, as I could continue working with him evenings, Saturdays, and Sundays. The Plutonium

Project work was very demanding, and was also emotionally

driven, since we were able to secure secret German war reports

on their project. Consequently, we were dedicated to this work,

and I remember 60-65-hour workweeks being normal. Then

I worked with Lewis from 7 until 10,11, or 12 p.m, (and he

210 Journal of Chemical Education came in regularly each evening) and every Saturday morning and afternoon. On Sundays I worked alone. At the end of our first year of research on phosphorescence I had recorded the spectra of more than 100 molecular species. Eighty-nine of these were published, and very few proved to be erroneous—in spite of the lack of refined techniques of chromatography, VPC, IR, NMR, mass spectrometry, etc. available today, In about July 1944 we began to write our first paper, and we started exploring singlet-triplet absorption. Looking at the long-wavelength edge of dye spectra proved difficult and fu- tile. We began to look at the absorption spectra in long tubes, first in a 1-ro cell, then in a 5-m optical cell rigged up in the corridor in front of our spectrometer.

.'„. /

First of all we must try, in our long tube, all sort of pure Uq- uids—such as toluene, alcohol (either ethyl or methyl) etc. Figure 3. G. N. Lewis on his 70th birthday. Photo by author. GNL Otto Redlich, of the Redlich-Teller vibrational frequency product rule, was living in Berkeley, and was called in for ex- which he was opening an ampule of /3-carotene obtained from pert advice. I believe it was he who suggested to Lewis that the Zechmeister {"Open in an Og-free atmosphere"). So I said, weak bands we were finding in 5 m of liquid benzene in the "This is Professor Lewis," pointing to Lewis in a frog-like pose visible and near UV (!) were really IR overtone bands. on the floor. Rediich was visibly embarrassed but introduced himself, Lewis exclaimed to me, "Oh, this is the man who improved my book!" Redlich had added a chapter on statistical thermodynamics to the German edition of Lewis and Randall. Rediich again blushed with embarrassment. As we began to think harder about singlet-triplet absorption and to develop the Einstein A/B relationship, we initiated a study of shorter-lived phosphorescent molecules for their correspondingly enhanced singlet-triplet absorptions

/••

Unfortunately it is now pretty sure that our bands are an extension of the molecular bands of benzene—but do benzene and perhaps dicklorethylene and acetone in the long tube anyway. «••>•• -'• GNL

Nevertheless, the observation of the IR overtone bands gave

us confidence that the 3400 A region weak absorption bands

found in liquid benzene were indeed electronic bands, which

could be correlated with our triple-singlet emission bands I think benzophenane is the most important substance to get ab-

found for benzene commencing in the same region. sorption of in long tube—perhaps only 20 cm.

Lewis knew Otto Redlich on two grounds. First, Jacob Bi-

geleisen had got his MS degree with Redlich at Washington

State in Pullman for a Raman study of the dissociation of

nitric acid—then he came to Berkeiey and proved to be one

of Lewis' best students Lewis ever had. The second was an In November 1944 we were well into our singlet-triplet ab-

instance which occurred when T was in the laboratory and a sorption studies, and Lewis personally began preparing some

dark-haired, robust Austrian gentleman appeared at my door nitrosoalkanes, which had a beautiful blue color, The ab-

and said with a heavy accent, "Where may I find the Herr sorption we thought to be singlet-triplet, but this has proved

Doktor Professor Lewis?" As it happened, Lewis was sitting to be wrong. I believe that the phosphorescences (IR) are,

on the floor with a bucket containing dry ice chips within

however, triplet-singlet.

Volume 61 Number 3 March 1984 211 Kasha: (CH3>2 Cg° in Dewar 1 hope the ice does not matter. If it does put it in cold acetone. Don't worry about lack of meniscus GNL The singlet-triplet absorption paper (24) was a landmark paper in correlating absorption spectroscopy with phosphorescence as a further spectroscopic proof of the intrinsic electronic character of the phosphorescent state as a triplet state. Although later research revealed far better examples of singlet-triplet absorption bands (we were hindered by lack of knowledge of spin-orbital Z-effects, which never entered our discussions), this work initiated the direct spectroscopic study of triplet states. By the end of February 1945 my work with Lewis was completed, my dissertation accepted, and all my energies were Kasha. devoted to an intensive phase of the Plutonium Project for the Your sample of bromnitrmopropane is in quartz tube in L.A. rest of 1945. [liquid air] It is clear and you could get absorption curve if you Lewis began thinking about the consequences of triplet wish G.N.L. state spin properties quite early. His sketches of the spin or- The Proof has come! ientations for the triplet state began popping up in the laboratory, one on his personal note pad, The proof of our first paper was very thrilling to receive. In December 1944 after the paper appeared in the Journal of the American Chemical Society Sam Weissman took the trouble to write Lewis a congratulatory letter on the paper. Lewis esteemed Weissman very highly, and his letter, stating that the phosphorescence and triplet state paper was "like a breath of fresh air," gave Lewis immense joy and satisfaction. He went around Gilman Hall with a fresh new smile for a week. I am sure that Lewis was very fascinated by the color effects in optical phenomena. He loved making the nitrosocom- pounds, and the deep sky blue color was very beautiful.

disregard the quartz one, which is my stock A dated sketch (July 18,1944) shows that at a time near GNL completion of our first triplet state paper, in discussing the expected magnetic properties of the triplet state he had

In about January 1945 our work on singlet-triplet absorp- sketched a Guoy balance. tion was coming to an end, and we began to write our second paper. Nitroso compounds' absorptions are displayed prom- July 18,1944 inently in this. work. IS, . /

/ /

••<- / / - Starting in March 1945, Melvin Calvin as our local param-

agnetism expert worked with Lewis on an attempt to measure

the paramagnetism of acid fluorescein in its phosphorescent

state. A communication was submitted by them June 16,1945

and published in the Journal of the American Chemical So-

212 Journal of Chemical Education ciety (25). They indicated a qualitative deflection into the cigar, these were all part of the visual physical chemistry that magnetic field in the right direction for the illuminated half Lewis enjoyed most. He confessed to me that organic mole- of the sample, but immediately afterwards observed a contrary cules had been his special joy in his later years, and how, be- deflection. In January 3.946, the main part of my plutonium cause he had failed a course in organic chemistry at Harvard research completed, I was able to join Lewis full time on this as a student, he had developed a lifetime dislike of organic pbotomagnetism determination. Lewis died shortly after- molecules—-much to his later regTet and chagrin. wards (Match 23,1946), and I, with Melvin Calvin's occasional overviewing, was able to complete a quantitative determina- Cautions on Heavy Instrumentation tion. The mathematical analysis was due almost entirely to Lewis had strong feelings against a researcher becoming too Lewis, but it took a major effort on my part, with cogent help attached to a large instrument or heavy research machinery. from Wiliiam Gwinn and Harrison Shull at two points, to Although he admired and made use of heavy instrumetation bring the calculation to a conclusion. Also, it took me two years at times, he felt that someone who developed such instru- of meticulous physical experimentation to unravel the side mentation was inclined to become a slave to and an exponent effects, eliminate them, and to refine the laborious quanti- of the instrument or machine. He preferred to be free to tative steps in the measurement. In our final day at the wander among available techniques and to wonder about ideas 20,000-Gauss magnet, the reproducibility of the Theorell and not be tied to one technique. For somewhat analogous boom displacement in the beam, its. dependence on light in- reasons he was prejudiced against complicated chemical tensity, and return to zero displacement in the dark, made syntheses as an aid to physical chemical research. He admired Calvin exclaim, "G. N. would have loved to be here today! He researchers who could make molecules, but he preferred to would have loved this experiment!" I wrote up the paper, and leave this to others so that he could devote himself maximally it was submitted in 1949 to the Journal of Chemical Physics, to developing and testing physico-chemical theories. He be- as a joint paper by Lewis, Calvin, and Kasha (26). An elegant lieved that if a theory was general enough, there should be refinement of this work was published in 1964 by Joussot- ample scope for the physical chemist to select a suitable Dubien and Lesdaux (27). sample from the chemical storerooms to test it.

Gilbert Lewis' Research Style Gilbert Newton Lewis' Last Day Mathematical Prowess I was working with G. N. Lewis on the Saturday afternoon, March 23,1946, when he died, and I find it worth recording At the blackboard during our conferences, at first in our the events of the last day of his life, particularly because there morning sessions and later in the evening sessions, Lewis' has been misinterpretation of the circumstances of his powerful analytical and intuitive scientific prowess shone death. through. There were two rather detailed mathematical problems that we worked on,, one being the derivation, from The Saturday morning was a particularly sunny one sci- the Einstein A and B coefficient relations, of the integrated entifically speaking. We had an unusually fruitful discussion, absorption-lifetime equation used in our second paper (we did and I especially remember being filled with so many ideas on not know that R. C, Tolroan had done this earlier). The other research that they seemed enough to sustain a year of work. was laying the analytical groundwork for a detailed photo- I had some new ideas on triplet-triplet absorption, and Lewis magnetism study which I completed with the overviewing and described more of his ideas on photomagnetism which I was help of Melvin Calvin after Lewis' death (26). I was at the then to undertake. blackboard groping with a difficult step a couple of times, and Lewis had a particular experiment he planned to do by Lewis seized the chalk and quickly showed in a few powerful himself at the vacuum bench that afternoon. A few days be- steps a way to its resolution. Although Lewis had published fore, he had read in the latest issue of Transactions of the some highly mathematical papers in his career (e.g., on rela- Faraday Society a paper which he showed me containing a tivity theory with Edwin Bidwell Wilson; statistical thermo- graph indicating that the dielectric constant of liquid hydro- dynamics with Joseph Mayer), his later years were spent on gen cyanide changes by a factor of over 100 in a certain ac- rather qualitative experimental studies, But the old ability cessible temperature range. Lewis said, "That would be a very was very much in evidence, hiding just beneath the surface. interesting medium in which to test the effect of dielectric constant on the color of dyes!" He planned that experiment for late Saturday afternoon. Overcoming Logical Barriers Lewis went to lunch with a distinguished guest and returned A special trick was used by Lewis when we got boxed into at 2 p.m. It was unusual for Lewis to go to the Faculty Club on a logical impasse, and it proved to be very effective. It did a Saturday. When he returned, he went to his vacuum bench happen quite frequently that our series of logical steps in some lab, which waa at the opposite end of the hall from his office, argument or development carried us seemingly to a stone wall: my laboratory being in between. A —•* B —• C-» D -* lj. Lewis would realize this, and he would I was working on the spectrophotometer in my laboratory. say, doing almost a little dance around a semi-circle ~i as if About every 20 minutes or so I walked by to see if everything to look at an object from behind: "Ijet's look at it backwards!" was all right Around 4 p.m. when I passed the vacuum bench So the argument was dissembled D -* C ->• B — A, and then room on my way downstairs, I glanced in and noticed Lewis suddenly H seemed clear that the steps should have been A missing. I began to step into the laboratory and got a notice- — B — C -* D' — E ~* solution, the blind alley becoming able whiff of HCN. Stepping back into the hall I saw Lewis' magically revealed by unraveling and reexamining the steps feet just visible behind the bench. I gave out a yell to the lab in the logic. at the end where I knew Daniel Cubiciotti was probably working, and I ran toward the hood with my nose clamped A Delayed Love Affair with Organic Molecules shut with my left hand. I threw a brick, which we kept as a Lewis died of a heart attack working one Saturday morning weight in the fume hood, through the window. Returning to in the spring of 1946 at his favorite place in the laboratory, the the hall I noticed the bottle of sodium bicarbonate in the hood, vacuum bench. He had just passed his 70th birthday. Lewis and rushed into the lab again, and covered the liquid on the loved to vacuum distill liquids from one flask to another, to vacuum bench table with bicarbonate, the active bubhling of sublime materials into reaction vessels, to watch color changes which suggested that liquid HCN had just spilled out. Shortly as reactions took place. The turning of the stopcocks, freezing afterwards Cubiciotti and I dragged Lewis into the hall and samples with liquid-air Dewars, warming up a solution with called for medical help. He had a serious welt in the middle a water bath, or even with a match which had just lit another of his forehead, indicating that he had fallen forward and hit

Volume 61 Number 3 March 1984 213 his head on a vacuum bench clamp. Lewis was dead on arrival Chronology of Key Discoveries in Triplet State Molecular in the University Hospital, and a medical autopsy indicated Spectroscopy clearly that he had died of a heart attack. We concluded that many minutes after he had died, the pressure had built up in Refer- the container of liquid HCN, from which the Dewar had been Year Authors) ence Research . removed, and the vessel dropped to the vacuum bench, spilling 1944 Lewis and Kasha H9) Phosphorescence the contents. assigned as T -» S Lewis' death was a very traumatic experience for me, and 1945 Lewis and Kasha (24) Singlet-triplet absorption because that evening I was previously invited to have dinner 1949 Lewis, Calvin, (26) Paramagnetism of triplet with Otto Rediich and his wife, I tried to cancel the visit. Re- Kasha stare dlich prevailed, and I owe a great deal to him for the warm, 1949 McClure 31) Z-effect on considerate, thoughtfui conversation that ensued that eve- phosphorescence lifetimes ning. 1950 Kasha {28) Z-effect on intersystem crossing Reception and Verifications of Triplet Stale Theory Kinetics of The American Chemical Society had planned a research radiationless symposium honoring G. N. Lewis to be held December 30 and transitions 31,1946, at Northwestern University in Chicago, but his death Uniqueness of changed the meeting plans. As his last research student to emitting states complete Work under his direction, I was invited to present 1952 Kasha m Environmental Z-effects the work on the triplet states of molecules. on triplet states )95B Hutchison and {33) EPB absorption Of triplet My presentation was the first of the meeting, and I was al- Mangum state (Crystals) lowed approximately 20 minutes. I knew that a very strong 1959 van der Waais and (34) £PR absorption ol triplet challenge was to be presented by James Pranck, but I had not de Groat state (glasses) expected that two hours of rebuttal of our work had been planned by Franck, followed by Robert Livingston, Eugene Rabinowtich, and Edward Teller. Each demonstrated the The difficulties of finding a triplet state BPE signal prob- impossibility of the Lewis and Kasha triplet state interpre- ably delayed full acceptance of triplet state ideas, but they tation on the basis of his knowledge, and Teller's detailed were finally resolved by the work of Hutchison and Mangum mathematical development of the theory of spin-orbital in- in 1958 (!) (33) and van der Waals and de Groot in 1959 (34). teraction seemed particularly devastating. I report in another 3 The subject of "Magnetic Properties of Triplet States" was place more details of this interesting confrontation and of reviewed in 1979 by Pratt (35). Pranck's prior meeting and relationship to Lewis. Robert Dellinger and Kasha (36) returned recently to the problem Mulliken, whom I met at this meeting, tried to defend our of vibrfttional potential effects which so dominated discussion thesis. The conference committee seemingly was suspicious before 1944 and concluded that only such large amplitude of my paper, I now realize, for although my paper (16) was motions as phenyl ring torsion would be inhibited by rigid presented first in the program, it appeared last in the pub- glass solvent cages. So all of the early preoccupation with lished volume! specific glass effects (aside from diffusional quenching) seems At the Faraday Society Discussion in 19491 presented (28) to have been unnecessary. my own new work on intersystem crossing, the radiationless Today triplet state studies of molecules have advanced to transition leading to triplet excitation, and a kinetic analysis highly refined stages, as exemplified in symposia (1967) (37) of the rates of radiationless processes with and without spin. and research treatises (1969) (38). The key historical steps in James Franck, a medalist at that meeting, was there to oppose the evolution of experiments and interpretation of triplet the triplet state idea again. Often repeated was the criticism states of organic molecules are summarized in the table. voiced by Radinowitch (1956) (29): Gilbert Lewis' Research Previews* The hypothesis of metastabfe (triplet) electronic states of organic molecules has been revived by Lewie and Kasha (1944); Gilbert Lewis' career, rich as it was in permanent contri- however, it seems that if the rule which prohibits singlet-triplet butions to the understanding of physical chemistry, also had transitions does not preclude the formation of the triplet state a most unorthodox pattern, not noted especially by anyone from the excited singiet state within Il)~? sec., it is unlikely to until now, but one which was typical of Lewis and which had delay its transformation into the singiet ground state for as iotlg a profound effect on his intellectual fertility and freshness as several seconds or even minutes. through his whole scientific life. Lewis previewed a research field in print, using his own analysis, sometimes without an It is obvious that these critics (which included Franck and exhaustive literature review, before embarking upon research Teller) had not considered the implications of intersystem in it. Most scientists think of reviewing a subject in print at crossing, whose kinetic analysis (28) so clearly indicated an the end of a long study and research period. Lewis told me he answer to the criticism. thought that approach could stifle originality. If a scientist Several spectroscbpk elements were provided which finally got an absolutely thorough knowledge of the literature before settled all suspicion concerning the validity of triplet state doing research, he was likely to acquire many of the prejudices assignment to organic molecule phosphorescence, The main and mental blocs of his predecessors. electronic spectra! proof lay in the Z-effect, since atomic number of substi tuents could be used for proof of spin-orbital For example, in the beginning of his career he wrote a paper, perturbation. Learning about the quantum mechanics of "Outlines of a New System of Thertnodynamic Chemistry" spin-orbital interaction from David Bohm in Berkeley in 1948, (40) in which the physical thermodynamic laws were applied I was able to show the Z-effect in intersystem crossing (28,30), to physico-chemical problems. This was .the origin of Lewis' and Don McClure immediately afterward was able to show the concepts of activity, activity coefficients, fugacity, partial Z-effect on phosphorescence lifetimes (31). A review (32) of molal free energy, etc. "Spin Intercombinations in Molecules" in 1956 revealed that Lewis told me that not long after completing his PhD at Terenin still believed that external "paramagnetic pertur- Harvard, he took a two-year appointment in Manila (as head bations" were essential to induce triplet state emission. of the Philippine Bureau of Weights and Measures) 1904-5—a most unorthodox start for a scientific career-—so that he could 3 See reference in footnote 2. think for himself. He worked his way through Walther

214 Journal of Chemical Education Nernst's "Physikalische Chemie" ("correcting all of the good nomenclature has enriched our scientific vocabulary, viz., mistakes"), hiked his way around the volcanos and country- Lewis introduced the term photon for light quantum (50). side of Luzon, and acquired a lifelong taste for Philippine ci- Gilbert Lewis once defined physical chemistry as encom- gars. Lewis then published his chemical thermodynamics passing "everything that is interesting." His own career overview paper and followed this with about 15 years of re- touched virtually every aspect of science, and in each he left search on chemical thermodynamics, culminating in the his mark. He is justly regarded as one of the key scientists in classic work, "Thermodynamics and the Free Energy of American history. It would be a great omission not to record Chemical Substances" (41)- Publication of this book marked the warmth and intellectual curiosity radiated by Lewis' the essential close of Lewis' researches in chemical thermo- personality. He epitomized the scientist of unlimited imagi- dynamics; he then turned his attention to other areas. His later nation, and the joy of working with him was to experience the works on statistical thermodynamics belong to another period life of the mind unhindered by pedestrian concerns. of his work. Lewis did indeed change research fields abruptly through Acknowledgment his career, usually prefacing a research period with his char- This paper was written and published under support of the acteristic penetrating research-proposal-overview paper. His U.S. Department of Energy, Division of Biomedical and En- Hater interest in isotopes could have been presaged by his vironmental Research, on Contract No. DE-AS-5-78EVG5855 paper, "The Chemistry of the Stars and the Evolution of with the Florida State University. Radioactive Substances" (42). Starting in 1933 he wrote an extensive series of papers on heavy hydrogen and heavy water, Literature Cited a paper'on lithium isotopes, and several papers on neutron (1) Sooner, H.,an, 762 {1916). {43). (3) I^owis, (i. N, Chem. Ken. , i, 231 (1924). (4) Kautsky,K,Ber.deutsch.cfcem.Get.,64,2083,2677on». Faraday Sac., 30,9!l (1934). In Lewis' summary book, "Valence and the Structure of (9) JdMi!Cfi61) Atoms and Molecules," (44) appear replica pages from Lewis' (10) ReM.C.J. Chem. Phys., IS, 1299 (1960). (11) Jabkmski,A.,Nai!(re, (SI,839(1933); Z.Phyaih,34,38 (198&). notebooks of the early 1900's, showing his early thoughts on (12) Jabionski, A., Bui And. Poi. $ci., Set. Sci. Math, Aatron. Phys., 6,589 (1958). electron arrangement in atoms and molecules. Lewis contin- (13) ftanck, J., and Livingston, R., J. Chem. Phys., 9,184 (1941). ued the development of ideas and nomenclature concerning (14) Forster, T., Nalurto'memchatten, 8,240 (1949). (15) Kasha, M.r Chem. Sen., 41,401 (1947). valence theory, especially the role of electron pairs, octets, odd (16) Lewis,G. N.,Lipkin,I).,andMagel,T.T, J. Amer.Chem.Sac.,»i,3005(1941). electron numbers, and diradical configurations in a series of (17) papers, with World War I interruptions, in 1913 (45) and then (18) 18,1 (1944) (Russian version). (19) Lewis, 0. ftf., and Kasha, M,,J. Amer. Chem. Sac... 86,2100 (1944). in 1916-17 (2). At a joint symposium of the American (20) FOrater.T., JViilurioiuenw/w/lCT, 31,166(19461. Chemical and Physical Societies and the American Academy (21) ¥6rster,T-, Naturwissenscha/teii.i,240(1943). (22) MeRae. E. G., and Kasha, M.,J.Chem.Pkys., 28,721 (1958). of Arts and Sciences in 1917 he threw the challenge to the Bohr (23! Cf.KBBhs,M,Rawls,H/R-andEl-Bayouroi,M. Ashraf.iWand Appi.Chem., 11, atom, showing that it could not explain molecular geometry 371 (1B65). (46). His chemical intuition set conditions on valency inter- (24) Lewis. C. N., and Kasha. M,, J. Amer. Chem. Soc., 67,994 (1946). (25) Lewis, G. N., and Calvin, M., J. Amur. Chem. Soc., ft, 1232(1945). actions for which only Quantum Mechanics was able to pro- (26! Lewis, 0. N, Calvin, M.. and Kasha, M., J. Chen. Phys., IT, B04 (1949). vide the basis. (27) .joussot-Dubien.J,, and Lesclaus. R., J. ehlm. phys. 61,1631 (1964). m> Kasha. M.. Faraday Soc. Discussion, Mo. 9, U (I960), (29) Habiriowitth. E,, '"PhcloaynlJiesis and Related PiucesseB," Academic Press, New York, Other research preview papers by Lewis include his paper 19B6, Vol. Ill, p. 753.790. on the electronic theory of acids and bases (47), preceding (30) Kasha, M.. "Paths of Moleculai Excitation," Radiation Res., Supplement 2, 213 experimental work with Glenn Seaborg on the subject. "The (i960). (31) McClure, D. S.../. Cftem. Phys., 17,905 (!949). Color of Organic Substances," (48) preceded almost a decade (32) Kasha, M., and McGlynn, S. P., Ann. Rev. Phys. Chem., 1,402 (1958). of research on the color and photochemistry of dyes. (33) Hutchison, C. A.. Jr., and Morgran, B. W., J. Chem. Phys., 29,952 (1958), (34) vartderWaals.J. A.,and De Kasha, M., J. Chem. Phjjs.,20,71 (1952). concentrate natural deuterium. Lewis then worked furiously (40) Ums,i}.~N.,Pnic.Ami:r. A:ad.,4,f,2B(19OT);Z.p*yBM.Chem.,«1 J29(1907). to establish his part of a claim to the discovery of heavy water (41) Lewis, G. N., and Randall, M F., "Thennodynaniks and the Free Eimrgy of Chemical Substances." McGraw-Hill Book Co.. New York, 1923. by doing every conceivable measurement. Finally ali of this U2) Lewis, O. N.,Publ.Aslron. Soc. Pacific, 34,309 HS2Z). work was reviewed in a comprehensive summary paper (49) Lewis,G.N.,Pftys. »™.,J6,897 (1931). (43! Lewis, G. N.,"Valence and the Structure of Atoms and Molecules/' Cheminal Catalog uncharacteristic of Lewis' research previews. Oo.,MewVoik,!9Za, (46!Lewis. G.N.,J./lnier. Chem. Sal:, »5,1-148 0913). Gilbert Newton Lewis typified the physical chemist of great M) lewis, G. N, Science, in, 297 (1917). intuition who was able to conceive of beautifully simple (47) Lewis, G. N.. J. Franklin Institute, 236, 293 (1938). models and concepts to explain complex physical and phys- H8) I<™is,a N.,and Calvin, M.. Chem, Reo.,2&, 273 (1S39). (49) Lewis,G. N., IX Congresao Internacional de Quimica Pura j Aplicada, Madrid, April ico-chemical phenomena. His conceptual contributions have 1934.' made lasting additions to our knowledge, and his aptness for (50) Lewis, G.ti., Nature, UH, 874 (102fi).

Volume 61 Number 3 March 1984 215 «#• A Simple Aid for Teaching the Theory of Atomic Structure

Hung-cheh Chiang and Ching-Hwel Tseng Institute of Chemistry, National Taiwan Normal University No. 88 Sec. 5, Roosevelt R&, Taipei, Taiwan, Republic of China

In the course of both high schooi and undergraduate college Example: 24Cr chemistry, students are often puzzled by the theory of atomic The student would choose the fourth card, because 24 is structure. In order to help them learn this more easily, we have smaller than the 36 required by the fifth card. There are 18 designed a simple demonstration to show the Pau!i exclusion electrons on the fourth card, thus the remaining six electrons principle, Hund's rule, quantum numbers, electronic energy of Cr will distribute themselves in the fourth energy level ac- levels, and electron configurations. The exercise involves cording to the rules. Rule one hanging valence electrons (represented by pieces of rubber) onto a game board which depicts the energy sequence of a ns < (n - 2)/ < (n - 1 )d < rap given atom. translates to 4s < 2/ <. M < ip Materials Because 2/ does not exist, the six electrons would be dis- 1 wooden plate (60 cm X 40 cm X 1 cm) tributed into the lowest available levels; two being placed in 33 iron naiis (1.5 cm in length) the 4s level and the remaining four into the 3d level. 2 rubber tubes of different colors (16cmX 1 cm), cut these into 3 4 1-cm pieces, yielding 16 pieces of each color Thus, the configuration of <^CT is shown to be (Ar)4s 3rf 7 blank index cards (see Fig. 3). With this the instructor can speak to the special stability of a half-filled sublevel and can show the students Sel-Up that, with 3d subieveis close to those of the 4s subieve!, the The game board, or orbital plate, is cut from a piece of wood. effect is large enough to allow "promotion" of a 4s electron to the M sublevel, giving Cr five 3d electrons. Thus, the accepted It is labeled as indicated in Figure 1, where n is the principal 5 quantum number, s, p, d, and / are the suborbits, and the configuration of -^Cr should be shown to be (Ar)4s'3d . number in parentheses after the suborbital designation indicates the angular momentum quantum number. The spin quantum number will be designated by using differently -Hmilinjontht na|jsl ._» plattraprmnt* colored pieces of rubber tubing which should be cut as de- the Blaetinnie scribed above. subtaval} Hammer the nails (which wi!I be used as holders for electrons) into position as noted. Each suborbit should have the number of electron nails that corresponds to the maximum number of electrons that can be held in that suborbit. Seven index cards should be labeled as shown in Figure 2. -"-woodanplot* These n-value cards will provide the players with standard information about the principal quantum numbers. Figure 1. Construction of the game board.

hole the Rules eleclrors Remember that the goal of this exercise is to fill out the 4- contained game board with cards and pieces of tubing so that it provides 6 within lha 6th a visual representation of the electron configuration within IH»>2 (Kr)M (MB4 Energy level the atom. Total the number of electrons within the given atom and compare to the electron totals on the re-value cards. The Figure 2. The seven Index cards representing the principal quantum num- ra-value card with a total that is either less than or equal to the bers. number of electrons in the atom of interest is then chosen and hung onto the upper left nail. If the number of electrons is equal to the n-value card, you are done. If it is not, determine how many more electrons are present. Take that number of pieces of cut rubber tubing and hang them, as representatives of valence electrons, on the nails according to the following energy sequence. Use differently colored pieces of tubing to represent electrons with opposite spin. The energy sequence of the sublevels with the same n- value is: NOTE: Ttw o raprawnti piece* ns < {n - 2)f < {n — t)d < np of rubber tubing if n < 6, then (n — 2)[ is absent if n < 4, both (ji — l)d and (n — 2)/ are absent Figure 3. The completed game board for ?JCr.

216 Journal of Chemical Education Photoelectrochemical Solar Cells

John T. McDevItt1 California Polytechnic Stale University, San Luis Obispo, CA 93407

We receive an enormous amount of solar energy from the The conversion of light to electrical or chemical energy in sun; the solar energy falling on the earth in a fortnight is PEC cells results from light in the visible region acting as an equivalent to the energy contained in the world's initial supply electron jump (4). The absorption of a photon by an atom (or of fossil fuels (1). Since the 1950's, much attention has been molecule) results in the pumping of an electron from its given to the possible use of photoelectrochemical effects to ground state orbital to a higher energy orbital. The wavelength convert solar energy directly into electric power or synthetic of light required for such a transition must have an associated fuels, and, as a result of the energy crisis, the study of pho- energy greater than or equal to that of the energy difference toelectrochemical phenomena has become increasingly more between the two orbitals. This energy, usually called the en- popular and important (2). This introduction to photoelec- ergy gap, Eg, is illustrated in Figure 1. trochemical celis will review topics pertaining to solar energy Light absorption within semiconductors occurs in a similar conversion as well as demonstrate the ease with which a fashion. In semiconductors, the moat energetic ground state working photoelectrochemieal ceil can be prepared. electrons are located in the valence band and higher energy There are numerous ways to convert the solar radiation levels are available in the conduction band. These two energy directly into electric power. The silicon soiar cell is the most bands are separated by an energy band gap, EB& in which no efficient in this respect, but its use is limited to the more en- electron energy levels are available. Photona with energy ergetic portion of the solar spectrum. Such solid state photo- greater than ERG are able to stimulate electrons from the voltaic cells have been quite useful in the space program and valence band to the conduction band. Photon absorption by now appear promising for terrestrial uses. Endothermic, semiconductors results not only in promotion electrons to the photochemicaily driven reactions which produce stable for conduction band but also in vacancies or holes in the valence isolatable) products (synthetic fuels) are an alternate method band (left by leaving electrons) as shown in Figure 2. of solar energy conversion. Although no economically prac- The result of this process in the production of an electron- tical, large-scale photoelectrochemical (PEC) cell has yet been hole pair (e~, h+) which may be denoted by the excited state discovered (3), a system of this type could provide a useful S*. The light may then be stored chemically if S* reacts by one source of energy. of the two following paths: A photoeiectrochemical effect is defined as the production of a change in electrode potential (on open circuit) or current S-+A — S+ + A- (on closed circuit) in an electrode/electrolyte system as a direct S*-I-D--S-+ D+ result of irradiation. The effect is caused by either a photochemical reaction producing electroactive products in the bulk where A and D are suitable acceptor and donor species, resolution or the presence of a photosensitive membrane or spectively. However, unless the back reaction between S+ and electrode. Soiat irradiation produces PEC effects on most, if A"" or S~ and D+ is slow, the energy associated with the pair not ail, surfaces. PEC effects at clean metal electrodes are very will be lost almost immediately as heat small, usually measured in mV and nA ranges, and are due to such processes as photoelectric emission from the metal sur- S4- + A- —S + A + A face or thermal effects of the radiation (2). Semiconductors, If the energy is to be stored hi chemical form, either the energy on the other hand, which may or may not be coated with a of activation for the back electron transfer must be large sensitizing dye, have been found to produce pronounced PEC thereby retarding this reaction, or the two components of the effects. Semiconductors therefore appear to be likely candidates for use in the conversion of light energy into electrical energy. This is reflected in the recent interest in this area 0-5). Conduction Band 1 Present address: Stanford University, Stanford CA 94305.

Excited Electrons

hp>EBG. 8G

Electrons

Ground State Valence Band Figure 1. Ortiftal energy diagrams showing the formation of an excited species when the ground state molecule is Irradiated with light of energy greater than Figure 2. Effects of light absorption within semiconductors. Electrons ars the energy gap. promoted to the conduction band and holes are formed in ine valence band.

Volume 61 Number 3 March 1984 217 redox coupie must be formed at some distance from each other of the system. This charge transfer results in a negatively as in a two-compartment cell. Unfortunately, excited states charged liquid surface layer and a positively charged solid (electron-hole pairs) are very short-lived and frequently re- surface and an electric field is thus established (Fig. 3), combine with a total loss of the captured energy into heat. When light of the proper energy impinges on an n-type Rapid separation of the electrons from the holes, such as might semiconductor/liquid interface, electrons are promoted from be promoted by an electrical field, roust be achieved in order the valence band to the conduction band of the semiconduc- to use the light efficiently. tor. The induced electric field, shown by the curvature of the Conversion of light energy to the highly desired electrical bands in Figure 4, drives the photoseparated electrons to the form has been one of the basic goals of solar energy research. bulk of the semiconductor and the hole to the surface. If the In order to achieve this goal, it is necessary to produce a flow solution contains an electroactive species, D, whose redox of electrons in an external circuit. Such a condition requires potentia! is above that of h+, then electron transfer can occur the formation and efficient separation of oppositely charged in the following fashion species (i.e., electrons and holes) which results in charge flow in the external circuit. Semiconductors are ideal candidates D + h+ -* D+ for use in such systems due to their ability to separate photogenerated charged species efficiently. A review of some of The excited electron can be transferred away from the bulk the basic semiconductor principles may help explain their semiconductor assisted by the induced field, and if the device function in PEC cells. is connected by a wire to a second electrode, it is possible for the light-energized electron to reduce a suitable acceptor Intrinsic or undoped semiconductors, like silicon and ger- manium, are essentially small band gap insulators. Such 0 + e~ -* 0- substances have completely filled valence bands and totally empty conduction bands with bands separated by a few Therefore, the overall process may be summarized by the electron volts. A semiconductor such as silicon, a group IVA following equation element, can be doped (impurity added) with a group VA el- + ement with one more electron, such as nitrogen, phosphorus, O + D-*-O--t-D or arsenic, or with a group III A element with one less electron such as boron, aluminum, or gallium. The group VA atom with If both 0 and R were water, the above equation would repre- its extra electron fits into the crystalline array of silicon atoms. sent the photolytic decomposition of water This extra electron is not required for bonding and is relatively free to migrate through the crystal. This produces an n-type semiconductor where the n denotes negatively charged mobile The solar spectrum does not possess the required energetics carriers, Doping silicon with a group IIIA element produces for efficient water splitting, at least not by a single photon a p-type semiconductor containing mobile vacancies as posi- mechanism. However, several other fuel-forming reactions tive holes in the crystal. requiring less energy for conversion have been studied (5). Unfortunately, many commercially attractive reactions re- Although the doping process retains electrical neutrality, quire too much energy to use the solar spectrum effectively since the dopants are neutral atoms, both mobile and sta- (see table). A band-gap energy equal to 1.1 eV or less is re- tionary charge carriers are provided. For example, when silicon quired for the most efficient use of the sun's energy (2). Only is doped with nitrogen, an n-type semiconductor results. The the oxidation of H2O by molecular oxygen approaches this extra electron from the nitrogen is relatively free to move ideality. Although no practical, large-scale system of this type throughout the crystal and can participate in charge con- exists at this time, the outlook appears promising. ductance. Nitrogen, however, also has one extra proton in the nucleus, which when introduced into the silicon array is rigidly The basic principles behind the operation of photovoltaic bound by the bonding mechanism and cannot participate in cells is quite similar to that described for semiconductor-liquid charge conduction. Doping of semiconductors results in the interfaces. Both systems require irradiation of a semicon- production of both stationary and mobile charge carriers; only ductor junction from which efficient charge separation occurs the mobile carriers can participate in charge conduction. A due to an induced electric field. In the case of the solid state similar treatment could also be given for p-type semicon- photovoltaic cells, the junction potential is obtained by doping ductors which have mobile holes and bound negative sites. the surface with a foreign material. This process, although These charge carriers are responsible for the use of semicon- quite efficient, is expensive and has limited the use of such ductors in a variety of electrical devices such as diodes, pho- devices. Semiconductor-liquid interfacial devices, on the other tovoltaic cells, light-emitting diodes (LED), and PEC cells. hand, are prepared quite simply by dipping a semiconductor into a solution containing.electroactive species. Their sim- When an n-type semiconductor is immersed in a solution, a number of the mobile electrons migrate from the solid surfaces to the solution in order to lower the chemical potential

Field Direction

X0.'. Redox D Level

Solution c

n-type Semiconductor Following Electronic Solution Equilibration n-type Before Contact Semiconductor Figure 3. Election transfer from n-type semiconductor to the solution with redox Figure 4, Electron-hole tlow upon irradiation of an n-iypa semiconductor im- couple D/D* producing an induced electric field. mersed Into solution with redox couple D/D+,

218 Journal of Chemical Education pHcity (and moderate cost) make them attractive candidates insulation of the semiconductor properties and the tendency for future use in solar energy conversion. for back electron transfer increases; too thin a layer results in The major hurdle associated with semiconductor-liquid, inadequate absorption. There are several chemical methods junctions involves the kinetics and energetics of the electron available to modify surfaces including chemiaorption, co.va- transfer. The semiconductor itself becomes susceptible to lently binding reactive compounds to surface functionality, oxidation if electron transfer from the donor species is too and redox polymerization, CarefulJy controOed experimental slow. An example of this type of anodic decomposition is conditions must be employed to attain the optimal thickness shown for CdS (an n-type semiconductor) of the insulating absorbing blanket A workable photoelectrochemical cell demonstrating many important aspects of these devices can be prepared quite easily. A stable liquid junction photocell using n-type silicon Stabilization may be obtained by adding reducing agents that as the photoanode and platinum as the counter electrode in can scavenge the photogenerated holes at a rate that prevents an ethanol solution of ferrocene can be used to demonstrate anodic decomposition. An alternative approach to this prob- the utility of such systems. A schematic diagram of such a lem has been to attach stable electroactive species directly to system is shown in Figure 5. The functioning of this system the surface of semiconductors via surface functional groups. is based on the following: Immersion of the n-type silicon in Ferrocene has been used to modify n-type silicon chemically the solution results in charge transfer of the mobile electrons and thereby suppress the growth of SiO* and bring about a from the silicon to the solution forming a negatively charged dramatic improvement in the photoanode stability of aqueous surface layer and leaving the semiconductor with a positive solutions (5). In addition, the derivatized silicon is able to surface region. Light of sufficient energy impinging on the oxidize anything oxidizable by ferricenium. negatively charged surface can cause the promotion of an The attachment of visible-light-absorbing dyes to the sur- electron from the valence band to the conduction band, face of a semiconductor is another possible solution to the leaving a hole where the electron once was. The induced problem of photolytic decomposition. Such a procedure in- electric field, spontaneously formed at the semiconductor/ volves sensitizing a larger band gap semiconductor with an liquid interface, forces the promoted electron away from the absorbing dye. Thus the dye, rather than the semiconductor, surface into the bulk and the hole towards the surface. At this is the light absorber and the semiconductor is not susceptible point a ferrocene molecule donates an electron to the vacancy to decomposition. The thickness of the sensitizing layer must and returns to the solution in the form of a ferricenium ion. be controlled very carefully. Too thick a coating results in the Meanwhile, the photoseparated electrons pass through an external circuit to the piatinum counter electrode and reduce the ferricenium back to ferrocene, as shown in Figure 6.

Typical Photochemical Reactions Experimental Standard Free Materials, Single-crystal, n-type silicon wafers (0.25 mm Reaction Energy Change, thick, 100 face) doped with Sb and having resistivity of 4-5 Raw Materials Fusi Mixture eV/moiecule 0 cm were donated by Signetics Corporation, Cupertino, CA. Ferrocene and absolute ethanol were used as received from H*0-> 2.46 commercial sources. Electrode and Cell Configuration, Electrical contact to the silicon electrode was made by depositing indium metal on the C02-*" co + yzos 2.66 back side of the semiconductor using a soldering iron, A copper wire was attached to the back with silver epoxy and the whole device was encased in a glass rod. All metallic surfaces N2 + 3 H20 -»- 2 Nrfe + % Oi 3.51 were insulated with regular epoxy so only the silicon was exposed to the electrolyte (M).i3 cm2). In all experiments a platinum counter electrode was utilized, positioned as close H2O + % °e -*• 1.24 as possible to the silicon photoanode, A one compartment cell with a capacity of approximately 50 cm3 of electrolyte was

COj + 2 H;O -*• CH3OH + % Oz 7.26 assembled from Plexiglas®. The electroactive solutions were composed of 0.07 M ferrocene and the amount of ferricenium

tK appropriate for each experiment dissolved in ethanol. Con- <»1a + 2 0, S.48 centrations were determined from optical density measurements (ferrocene: Amax = 450 nm, £450 *= 901 mol"1 cm; ferri- 1 cenium: Amat = 618 nm, %]e = 4501 mot*" cm). AH electrodes

Electrolyte

-a LIGHT Pt Pt K Fe(Cp) Electrode 9 Electrode

Photoanode Soiution Figure 5. Schematic representation of a photoelectrochemtaal cell for converting tight energy into electricity using n-iype silicon as the photoanode ana platinum as the reversible counter electrode. Both electrodes are Immersed In Figure 6. Conversion of light Into electrical energy for rt-type silicon photoanode a ferrocene/ferrlcenium electrolyte. Immersed In ferrocene/ferrlcenSum (FefC^

Volume 61 Number 3 March 1984 219 were etched in concentrated hydrofluoric acid and rinsed with crease significantly. Since rigorous precautions were not taken ethanol immediately before the experiments. A 0.1 M ferri- to eliminate moisture and dissolved oxygen from the system, cenium sulfate stock solution was prepared hy adding 3.3 ml it was imperative that the oxidation of ferrocene was kineti- of concentrated sulfuric acid to 1.86 g of ferrocene, then di- cally favored over oxide formation. luting to exactly 100 ml with ethanol. Long-term stability charcteristdcs of the silicon photoanodes Experiments. Stability of the silicon photoanodes was de- was established by irradiating the semiconductor electrode termined in ethano! solutions containing 0.07 M ferrocene and in anhydrous ethanol containing the ferrocene/ferricenium 0.001 M ferricenium sulfate. Input light intensities of ~25 redox couple. Figure 7 shows the electrode potential obtained 2 mW/em , obtained from a simple spectrophotometer light over the course of several hours, Also shown here for com- source and simple lenses, were utilized throughout these ex- parison is the electrode potential under dark conditions. In- periments. The voltage was measured with a strip chart re- deed, the ability of ferrocene to capture photogenerated holes corder. Current, in series with the recorder, was measured with preventing SiC>2 formation is quite good as demonstrated by a digital multimeter. the stability of this device. Kinetics of SiO2 formation, A S1O2 layer spontaneously SiOa can be removed from the semiconductor surface to forms on the surface of the semiconductor. This oxide layer restore original activity. This may be accomplished electro- was electrochemicaHy removed from the semiconductor sur- chemically or with the use of HF etching. Both methods have face by applying a potential difference of 15 V across the proven successful in restoring the efficiency of the system photoanode and the platinum electrode immersed in ethanolic following oxide passivation. The latter method has been used ferrocene solutions. With the negative terminal attached to almost exclusively by previous authors, but the former offers the silicon electrode and the positive to the platinum, gas insight into the kinetics and energetics of oxide formation. evolution (presumably hydrogen) from the reduction of water After a negative potential is applied to the photoanode, the along with SiO2 reduction to silicon was observed at the silicon efficiency of the device increases significantly. This is most

electrode, and the oxidation of ferrocene to ferricenium was likely due to the reduction of SiO2 to free silicon observed at the platinum surface. Upon removal of the applied + potential, the open circuit voltage was monitored as a function SiOa + 4 H + 4 «r ~* Si + 2 H2O of time. A decrease in the output voltage, presumably due to oxide formation, was observed in ail experiments. The rate of Following reductive treatment of the photoanode, the open this decrease was used to monitor the kinetics of oxide for- circuit voltage decreases exponentially, gradually leveling off mation. at an equilibrium value as the passivating oxide layer reforms. The effects of water content on the rate of oxide formation The results of the three experiments testing effects of were determined by observing the voltage characteristics after oxygen and water on the rate of oxide formation have been water (5,5 M) was added to the helium-purged ethanolic fer- summarized in Figure 8. Oxygen content was found to have rocene/ferricenium solution. In a similar fashion, the effects little effect on the rate of oxide formation, showing photopo- of oxygen were determined following an oxygen purge of the tential characteristics similar to the O2/H2O free reference. ethanolic solution. Solutions containing water, on the other hand, showed signs of increased oxide formation. Results and Discussion Jn summary, a PEC cell demonstrating many important Most nonoxide semiconductors used in PEC devices are aspects of the chemical solar cells can be easily assembled with susceptible to photolytic decomposition. In the case of n-type 11-type silicon as the photoanode and a platinum counter silicon photoanodes, the semiconductor itself can be oxidized electrode, both immersed in ethanolic ferrocene/ferricenium if the photogenerated holes are not quenched prior to elec- solutions. A system of this type can be used to convert solar trode decomposition (oxide formation) power directly into electrical energy for an extended period of time. Unfortunately, such systems are plagued with pho- + Si -t- 2 H2O — SiOs + 4 e~ + 4 H tolytic decomposition of the photosensitive electrode which limits their efficiency. This is the major scientific hurdle as- Oxide formation may also be produced by the reaction of sil- sociated with these devices. The sun can contribute greatly icon with dissolved oxygen to our energy needs if an efficient, inexpensive, workable

Si + 02 - SiO3 SiO2 formation has the effect of insulating the surface. As the 1200 oxide layer thickens, the photocurrent and voltage levels de-

500

^400' 5 -300 — • o &200 O 0 5 10 15 Time/sec a. Figure 8. Plats of photopotenilal against time immediately following electrochemical removal of the oxkte layer from the silicon electrode. These plots display the rate at which oxide reforms on the silicon electrodes under various 0 12 3 4 conditions, noted by the decrease In the photopotenSal as the passivatlng oxide Irradiation time /hr refoims.Run 1(O)exhlbits the kineteobteir^w^aheltam^iffged anhydrous Figure 7. Plots of open circuit photopotantlal against time for n-fype silicon electrolyte; run 2 {—), with an anhydrous oxygen-saturaled electroiyte; and run electrode Immersed In 0.07 Mferrooene and 0,001 Mfeiricenium sulfate. For 3 (•), with a solution containing 5.5 MH/i. Each run was performed in ethanol run 1 <•), 0.13 cm* of rvtype silicon was irradiated with 25 mW/cn^ white light. containing 0.07 Mlerrocene and 0.001 Mfeiricenium sulfate with Incklent light : Run 2 (O) was obtained under dark conditions. intensities of ~25 rstW/cro .

220 Journal of Chemical Education system can be devised. The present work suggests that such Literature Cited a system may soon be developed, (1) Hubhard, M. K., The Environmental and Biological Forum 70-71," US. Atomic Energy Commission, 1*72. (2) Archer, M. D., J. Appl. JSfec.S, 17 (1976). Acknowledgment (3} Zaren, A. M.r "Introduction to the Utilization of Solar Energy," McGrew Co., New York, 1951. Hi Bard, Alan J.. Science, 387,139 {1980). The author gratefully acknowledges helpful discussion with (5) WrigMon. M. W., Chan. Eng. Nws, Sept, 3,1979. 1 Dane Jones, Ronald Brown, Nathan Lewis and extends special (6) Wiighton,M,8.,Lei!B,K.D.,Eili8,A.B,a»dBo)ta,J.M.,/ Ww.JVattJin«(.S«.t/.S.A, thanks to Ralph Lovelace of Signetics Corporation, Cupertino, 7<, 4116 0977). 17) Wright™, M. S, Bolts, J. M.. Bocarsly, A. a. Palaszotto, M. C. Walton, E. G., and Ijjwia, CA, for donating the silicon wafers. N. K., J. Amer. Chum. Sot., 101,137S (1978).

Thermodynamic Inefficiency of Conversion of Solar Energy to Work

Arthur W. Adamson, James Namnath, V. J. Shastry, and Vida Slawson University of Southern California, Cos Angeles, CA 90089

It might be thought that photon energy should be pure energy. The approximation of equating energy and free-energy energy, that is, should have no entropic content, and hence differences is discussed later in this paper. As we discovered a+ that solar energy should in principle be entirely convertible some years ago (8), [Ru(bpy)a j* is a good reducing agent, into useful work. A more conservative guess might be that good enough to reduce water. The product, ftu(bpy)a3+, is a since solar energy relates to radiation from a 8000 K source, good oxidizing agent, good enough to oxidize water. The a Carnot efficiency factor of about ((6000 - 298)/6000) = 0.95 simple scheme, might apply. Neither of the preceding statements is correct 2+ + for a quantum or threshold solar device, but it is true that iRu(bPy)3 ]* + H3O ~- Ru(bpy)33+ + 'AHa + H2O there is a thermodynamic limitation to the efficiency with -A0- m = t°298 = 0.84V (3) which light energy can be converted into work. The limitation 2 3+ + + depends on the intensity of the radiation and its wavelength Ru(bpy)3 + % H2O - Ru(bpy)32 + % O2 + H3O D O and can be substantial. ~AG 298 = * 398^ 0.03V (4) Chemists practicing in the solar energy field seem generally not to pay much attention to this limitation. Its treatment is gives, in combination with eqn. (2), the net reaction not new {1-4), but analyses seem not to have appeared in easily accessible chemical literature. A useful review, however, V4 Os - « -1.23V (5) is by Boiton and co-workers (5). In addition, the various treatments have been couched in terms of black-body radia- (the potentials are from ref. (9)). In effect, Ru(bpy)a2+ acts tion fluxes or semi-conductor solar cell analyses, and the as a catalyst whereby light energy is used to split water. The language has been more that of physics than of chemistry. In produced hydrogen couid be used as a fuel to run an engine. this paper, we present a more chemical and less sophisticated There are many difficulties with the simple scheme above, but approach. a more complicated version has shown some success f 70). The system is cited here merely to illustrate how the energy con- Einstein DkJ Us In tained in an excited state may be used to produce useful work. The thermodynamic limitation is usually mingled with We do not concern ourselves here with the many complexities another kind of efficiency limitation, and it seems well to and inefficiencies of actual conversion schemes. Rather, we separate the two aspects. This other limitation is a conse- are after some basic limitations upon which no scheme can quence of the quantum aspect of nature, as embodied in improve. Einstein's Saw of photochemical equivalence (6, 7). Light Returning to the type reaction of eqn. (1), if the transition energy comes in quantum packets of value hv, where h is were between two specific states, we would see a single sharp Planck's constant and v is the frequency. Photochemistry line absorption spectrum of A. In this case, only light of fre- involves putting a molecule in an excited state of some definite quency corresponding to hv * E* would be absorbed, ne- energy E* above the ground state. (In the case of a semicon- glecting line broadening inherent in the uncertainty principle. ductor solar cell, there is a minimum energy E* of promotion In practice, however, we are dealing with at least diatomic and of an electron into the conduction band.) Einstein's law af- usually with polyatomic molecules and the electronic excited firms that unless the energy hv is at least equal toE* there can state A* will have a different bond length in the diatomic case, be no absorption of light energy. and different bond lengths and bond angles in the polyatomic Pursuing this last aspect, suppose that we have the photo- one. Thus, A* will be geometrically distorted relative to the chemical system ground state A. The situation is illustrated in Figure 1. The Franck-Condon principle tells us that no appreciable A-*-A* (1) nuclear motion occurs during the absorption of a light quantum, that is, that the transition is a "vertical" one. The con- where the electronic excited state A* is to be the source of sequence, shown in Figure 1, is that light absorption produces chemical or electrochemical energy. Nowadays, for example, a distribution of vibrationaliy excited A* molecules. The ex- many inorganic photochemists are exploring the case of perimental observation is that the absorption bands are broad, as illustrated for the case of Ru(bpy)a2+ in Figure 2. Our en- 2+ 2t ergy E* is now actually that of the transition from the v = 0 Ru =0 level of A*, or of the so-called zero-zero where bpy denotes 2,2'-bipyridine, and G° is standard free transition (where v denotes vibrational quantum number).

Volume 61 Number 3 March 1984 221 This transition is not totally forbidden by the Franek-Condon rium with their surroundings. This collection is, in effect, a principle and can, in fact, sometimes be seen as a weak feature thermodynamic ensemble having entropy and hence free on the long wavelength tail of an absorption band. In the case energy as well as energy. This excited state ensemble has been 2+ 1 of Ru(bpy)a , E* is about 50 kcal mole" , corresponding to called a thermally equiJibrated excited state; we have used the aX*of570nm. special term thexi state (11). A thexi state is a good chemical Einstein's law telis us that light of wavelength longer than species; it is, in effect, an isomer of the ground state. Thexi X* wiil not be absorbed (neglecting the small tail of the ab- states, as noted above, have well-defined energy, entropy, and sorption band beyond X*). Now, however, light of wavelength free energy. They have standard oxidation and reduction shorter than X* will be absorbed because of the broad nature potentials; they have a definite structure, reaction chemistry, of the absorption band (for example, 450 nm radiation in the absorption spectrum, etc., ail of which may be different from case of Fig. 2). The produced A* is vibrationally excited, but the corresponding ground state properties. One special feature this vibrationai energy is ordinarily very quickly lost to the of a thexi state is that it may be able to return to the ground solvent medium {within picoseconds). We thus end up with state A by emission of light. This is true for [Ru(bpy)3a+]*, for non-vibrationally excited, that is, A* species. Moreover, this example, and the emission spectrum is included in Figure is apt to be the situation even if we are populating some higher 2, excited state by using light of yet shorter wavelength (such as We are now at the point where the limitation imposed by light of below 300 nm in the case of Fig. 2). Usually (although Einstein's law can be examined. The problem is that solar light not always), crossing from one excited state system to another covers a wide energy spectrum, being essentially black-body occurs so that we still end up with A*. radiation. A standard intensity spectrum for light incident on A further, and important point is that we actually are the earth's surface is shown in Figure 3. The situation is that dealing with a collection of A* molecules in thermal equilifa- ai! light of wavelength greater than X* is wasted since it cannot be absorbed at all. Because of the typical broadness of absorption bands, we can assume that ali light of smaller wavelength can be completely absorbed. However, the energy content in excess of E* per mole of light quanta is also wasted. This excess energy goes into vibrationa! excitation of A*, an excitation which is promptly lost as heat to the surroundings. We will limit ourselves to the case of an isothermal system, so that this heat is unavailable to do useful work.

The above qualitative exposition can be made quantitative in the form of the integral, E f * 7(X)dX IE=- (6) r

where 7(X) is the intensity of solar radiation in incident quanta per wavelength interval and E(\) is given by ftc/X. The coefficient fs is the efficiency factor resulting from this working of Einstein's law. This integral has been evaluated as a function of E* (see Ref. (5), for example), ft maximizes at/js = 0.44 for X* about 1100 nm. (There is a second-order dependence on whether we are talking about the solar spectrum reaching the earth's surface, or that just outside the earth's atmosphere.) It is probably no coincidence that the chlorophyll of plants . —DISTORTION *• absorbs in the red, so that fe is relatively large. An interesting Figure 1. Energy fsvel diagram showing the effect of excited slate distortion. point is that while f% is thus made large, light of such long Straight arrows represent a radiative process and wavy arrows non-radiative wavelength does not carry enough energy per quantum to do processes. the needed photochemistry. Plants solve the problem by means of a complex chain of molecular events whereby two or more photons are used'to provide the energy needed for the

nm Figure 3. The spectral distribution ot solar energy with the sun at 60° from the Figure 2. Room temperature absorption (-•-) and emission {—) spectra ot zenith (72). (The dips in the spectra are due io absorption by various atmospheric aqueous Bu(bpy)3Ci;. and solar atmospheric species.)

222 Journal of Chemical Education reduction of COa, Man-contrived chemical solar energy con- Further, AG = ~3S and AG° = -~3£D, and we can replace version systems, however, are more likely to take the AG° by its equivalent from eqn. (8). We thus obtain mechanistically simpler route of doing the job with just one photon per primary reaction event. There is a trade-off, AG = RT In (9) however, in that the required photon energy is increased, with a A* • 2+ a corresponding reduction in /#. To take the Ru(bpy)3 where wrev is the reversible work. The activity coefficients of system as an example, A*, is now 570 nm, and /E has dropped A** and A+*eq can be taken to he the same (both solutions will 1 + + + to 0.20. be very dilute in A *), as can those of A eq and A {the total concentration is the same in the two compartments), eqri. (9) simplifies to The Ther modynarrric Limitation We come now to the additional limitation that is the focus RTln{x'(l - (« (10) of this paper. Any means of reversible generation of work where x* is the fraction present as At*. would do, but for convenience of exposition, let us assume the For any system likely to fae of interest, #* will be very following. We have the cell eq small, and likewise x* {see Example below). Equation (10) Solution of AX reduces to

concentrations are = Pt/C(s) !"rev RT llj(**A*(iq) (11) (A**} and (A+V Equation (11) is essentially eqn. {16) of Ref. (5) and eqn. (6) of Ref. (2), obtained by a more general route. The simple assumption is that the excited state energy, E*, Solution of AX under is entirely available for work, and we now want to compare this C(s)/M/Pt amount of work to wiev. We can structure this assumption irradiation. Concentrations more specif iealiy as follows. First, we say that A+ is converted are {A+) and (A+*). entirely to A+* so that the energy producing process A+* •-• A+ is between species at the same concentration, that is, there We take species A as actually to be a cation, A+, so we can be is no entropy of dilution difference. We can take the conditions dealing with an electrolyte; the anion, X~, is purely a spectator of A+ and A+* to be their respective standard states. Next, we species. C is a one-electron-reduced form of A+. We suppose neglect any internal entropy difference between A+ and A+*, that the couple C(s)/A(solution) is reversible at a Pt electrode, that is, we take AS" to be zero4 and equate energy and en- and that the electrode M is such that the couple C(s)/ thalpy.5 With these assumptions, E* = ~~AGa, A+*(solution)/M is reversible while the couple C(s>/A+(solution)/M is not, that is, that electrode M is polarized with the The thermodynamic efficiency factor, /•[•, can now be respect to the second process.2 The dashed vertical line in the written as cell denotes a liquid junction. h = (12) The right-hand solution is under steady irradiation of wavelength X*, and is of sufficient concentration that the in- or cident light is completely absorbed by A+. The irradiation builds up a concentration of A+* to some value (A+*) and at (13) this point the cell is allowed to operate, drawing just sufficient (We have approximated OA+ by current to maintain (A+*) at a steady state value. The whole system is at constant temperature arid, under the steady state condition, light energy is being converted to useful work. + A Numerical Example A potential problem is that A * can in general disappear a+ by other processes than the ceE reaction. A+* can, for example, We can build an example around the Ru(bpy)a case. We return to A+ by light emission or by non-radiative relaxation. take X* to be 570 nm or E* - 50 kcal per mole of light quanta. These are first order processes with rate constants k, and knr, respectively, and the sum, k - kt + fenr, determines the rate + at which A * would ordinarily disappear. The requirement 1 + )n reading articles on solar energy conversion, ii is well to remember here is that the cell reaction must keep (A *) small enough that authors generally do not irtclude fe in their efficiency statements. that &(A+*) is negligible compared with the rat* of the pho- Rather, the efficiency reported is that for complete absorption of light tochemical reaction {see Example below). of optimum wavelength, or around A". (Few example, Graetzei and co-workers report this type of efficiency as —0.1 for their Ru(»py) 2+ We want our idealized cell to be one which can operate 3 system (10).} Such an efficiency statement is useful, of course, in under steady state conditions. To accomplish this, suppose evaluating the chemical performance of the particular system; it is that, essentially all of the current across the liquid junction is misleading, however, in that If the C factor were to be included, the + 3 e carried by A . The cell processes per faraday are as follows. practical Interest oi the system might be treatiy diminished. + The right-hand compartment gains one mole of A by trans- 2 + + + + Remember that A * Is an isomer of A which can have quite difference, loses one mole of A by photoexcitation to A *, and ferent properties from those of A+. As an example, A+ and A* * migftt + + this mole of A * is reduced to C(s). The left-hand compart- have acidic protons, but the pKg of A * might be very different from ment gains one mole of A* by oxidation of C(s) and loses one that of A+, so that In a given solution, the degree of dissociation .would mole of A* by transference. There is thus no net change in be very different. This difference might allow electrode M to be polarized + either compartment. with respection to the reduction of A but reversible with respect to + + + that of A ", Such selectivity ia a matter of kinetics, and while the The net cell reaction is just A * = A , and the corre- condition might be difficult to achieve in practice, it Is a thermody- sponding emf is namlcally permissible one. 3 + RT, The condition of near unitary transference number for A might C(s)/A* (solution) ' (7) be achieved, for example, by using a cation exchange membrane to separate the two compartments. where o denotes activity. In the left-hand solution A+* is in 4 This could be a dangerous assumption. One might guess that AS° + + 4 equilibrium with A , and for the process A *eq = A "^, we is apt to be negative on the grounds that some bond weakening should have occur in the excited state, with concomitant reduction in />• 5 This amounts to neglecting any partfa! molal volume difference + + AG° = G V ~ G"A+ = -RT In K, K = aK+JaA*; (8) between A and A *.

Volume 61 Number 3 March 1984 223 If this is taken also to be ~AG°, then 1/K at 25°C is 2.13 X angle subtended by the sun's disk, assuming a perfect f 1 lens. 31 6 3 4 10™ . This is aiso the value of x *eq. Since as is about 9.3 X 1CT , this factor is 1.16.X 10 , giving a 4 The average soiar power at noon in the general latitude of news;' value of 1.16 X 10~ , The new /- now has the fairly 2 the U.S. is about 750 watt irT (12). With fE = 0.20, about 150 respectable value of 0.89. The combined efficiency fgfy is 0.16, 7 watt m~s might be available to produce [Ru(bpy);j2+j*. The 0-15, and 0.18 for the three cases. 2+ molar extinction coefficient of Ru(bpy)3 is quite large (note We might, alternatively, consider a system of smaller E* Fig. 2), and we can suppose that a layer 1 mm thick of 0.001 value. For example, if we take the A* of maximum /#, or 1100 M solution will be totally absorbing. One liter of solution will nm, E* becomes 26 kcal mole*1. With the same a:* value of 1 2 thus cover 1 m and in this solution (150)/4.184) (50,000) = X 10~8, /•/' is now only 0.58. The combined efficiency fsfr 4 1 2+ 7.1? X SO" mol sec" of [Ru(bpy)3 ]* will be produced. becomes 0.26. Thus, the gain in/E is largely offset by the loss We can now estimate a practical value of**. The rate of in [T- Other, more sophisticated analyses, give the maximum production of [Ru(bpy)a2+]*, is 7.17 X 10"~4 mole/liter-sec, and fefr value as about 0.34 (5). is also to be the rate of its removal in our hypothetical cell. This rate must comfortably exceed the combined rate of the Conclusion various dissipative processes. That is, we want 7.17 X 10~4» A(A+*). The minimum value of ft is given by 1/T, where r is The above has been presented as an interesting exercise in the emission lifetime in the absence of specific quenchers or an uncommon area of first and second law thermodynamics. excited state reactants. This lifetime is about 600 nsec at 25°C The result has also some importance in that it tells us that no and in an aqueous medium, giving a minimum k value of 1.67 single chemical system converting solar energy into useful X 106 sec"1. Our requirement is that (A+*) « (7.17 X 10™*)/ work, can be very efficient. By contrast, if solar energy is ab- (1.67 X 106) or << 4.29 X 10*10. We can lake 1 X 10~n M as a sorbed as heat for heating purposes then it is almost com- reasonable maximum value for (A+*), and a corresponding pletely used (13). To the extent that we use fuel for heating maximum value for x* of (1 X 10™n)/{0.001) =• I X 10~8. purposes it should be far more efficient to release that fuel by using solar heating than to replace it by solar energy conver- Returning to eqn. (13), we obtain sion devices. If = (1 X I0-8)/!n(2.13 x 10-37)) = 0.78 (14) There is thus an additional 22% ioss of efficiency due essen- Acknowledgment tially to the difference in entropy of dilution of A"1"*^ and A+*. It is apleasure to acknowledge very helpful discussions with The efficiency fr varies with light intensity. If the intensity J. R. Bolton and with J. Pineberg. were reduced one-hundredfold, so that x* = 1 X 10~10, then fr = 0.73. Conversely, one might think of focusing" sunlight Literature Cited so as to increase the intensity. The sun is not a point source, and it turns out that the maximum factor by which the in- (1) fiaught, A. F., Abstracts. Third Int. Conf. Pholochem. Conv. Stor. Soiar Energy, tgdisnr: 2 Connoli, J. 3.) Boulder, Colorado, August 1980. tensity can be so increased is just l/« where w is the solid (2) Rons, R, T., and Hsiao,T. I,., J. ApplPhys.,ii, 4183 (19771. (31 Shockley, W., and Queisser, H. J, J. AppL Phys,, 32,510 (1977). (4) Trivial), D., and Fiinn. P. A., in "Solar Energy Research," (ffdiiors. Danieln, F., aui 6 37 Ihiffie, J. A.), Univ. t>f Wisconsin Press, Madison, Wisconsin, 1955. While 2.13 X 1O~ Is. unimaginatively small as a laboratory (5) Bolion. J. R, Haught. A. P., and Koas, R. T.. in "Phptodiemkot Conversion and Storage number, it represents a perfectly good alternative thermociynamic of Solar Energy" (Editor: Connolly, J. S,), Academic Pfeeu, 1981. statement to thai of 1/K. (fit Giass&tone, S., "Textbook of Physical Chemistry," D. Van Noatrand Co., Now Votk, 7 194«,p. USJ, A typical nuclear or coal-fired power plant might put out 1000 (7) Ada-son, A. W., "A Textbook of Physical Cliemistiy," 2nd ed., Academic Press, 1979. megawatts Of power (for example, one of the San Onofre units in Cal- p. 666. a+ ifornia). At 16% efficiency, the toea>Ru{bpy)3 device could deliver (B! GafneJ', H. D., and Adamson, A. W., J. Amer. Ckem. Soc.U, 8238 (1972). z (9) SuEin, N., and Creut!, C. Pure end Applied Chem., 52,2717 (I960). about 0.16 X 750 or about 100 watt m~ . For 1000 megawatts, one (10> Bor£arello, g., Kiwi, J.. Peliiietti. F., Visea, M., and Oraetzel, M.. J. Ainer. CJiem. Soc.. would need 1 X 107meor 10 km2 of 1-mm thick solution, or 1 X 107 liters of 0.001 W solution, corresponding to aboui 1 X 10* moles or 7 (li) Adamson, A. W., Adi., in Ctem., 150,12S (1976). tons of a salt of the complex. At the current price of about $10 per gram, Hi) Ref. (?>,p.826. this amounts to a cost of $65 mliiion (assuming that there is that much (53) Hauta&l. R. R., King, R.B., and Kutal, Cm "Solar Energy; Conversion and Staragfi," {Editors: Haulala, R. R., King, R. B., and Kutal, C), Hnmano Press. Clifton, NJ, ruthenium around!) 1978,

Joint Great Lakes/Central Regional AGS Meeting The Division of Chemical Education has organized a stellar prttpam for the Joint Gieat Lakes/Central Regional ACS Meeting being held in Kalamazoo, Ml, May 23-25,1984. The following symposia are planned: Coping With CPT Guidelines, Derek A. Davenport, Chair; Using Computers Cieativeiy, John W. Moore, Chair; The Analytical Curriculum, Roland Hirsch and Harry L. Pardue, Co-Chairs; Environmental Update: Problems of the Great Lakes Region, John W, Moore, Chair; Chemistry for Allied Health Sciences, Anne Deckard, Chair, Spirited discussions are expected on incorporation of descriptive inorganic chemistry and computer literacy into the curriculum; how and whether the current analytical chemistry curriculum ought to be changed; the problems of LoveCanai, PCBs, dioxuij and hazardous materials; and appropriate courses for those aiming at health-reiated careers. In addition there will be a high school chemistry teachers' day with a program on chemical demonstrations appropriate for the high school classroom. Those presenting the demonstrations will be: Glen Dirreen, Douglas Halsted, Doris Kolb, and David Tanis—two college teachers and two high school teachers. The high schooJ symposium will take place the morning of Friday, May 25. All teachers are invited to attend, whether or not they are members of ACS or DivCHED. For more information about meeting registration, accommodations in Kalamazoo, other divisions' programs, etc., please contact Dr. Lydia E, M. Hines, General Chair, The Upjohn Company 7284-126-6, Kaiarnazoo, MI 49001, (616) 385- 7818.

224 Journal of Chemical Education. The Evaluation of Empirical Resonance Energies as Reaction Enthalpies with Particular Reference to Benzene

Philip George Biology Department, University of Pennsylvania, Philadelphia, PA 19104 Charles W. Bock and Mends! Trachiman Chemistry Department, Philadelphia College of Textiles & Science, Philadelphia, PA 19144

The knowledge that the absence of double-bond reactivity on the properties of individual bonds inferred from calcula- in benzene is associated with an enhanced thermochemical tions using, for example, the ir-electron approximation, or stability dates back to the 1890's. Stohmann (1) showed that calculated using model structures with idealized bonding or in the three successive hydrogenation steps whereby benzene hypothetical reference structures such as an infinitely large is converted into cyclohexane, and terephthalic acid into cyclic polyene. Empirical resonance energies can be calculated hexahydroterephthalic acid, the first step is far less exother- theoretically simply as the difference between the energies of mic than the othef two, if not endothermic (see Table 1). product and reactant species. Ab initio calculations are well Furthermore, the second and third steps have reaction heats suited for this purpose because all electrons are taken into much more like those for simple acyclic olefins, e.g., ethylene account. -31.9 and propylene -32.5 kcai mol"1 f 1). In later, more accurate experiments, Kistiakowsky et al. found that the first step for benzene was also endothermic (3). Stabilization Energies Calculated from Bond Energies 1 With the advent of valence-bond theory in the 193G's this AHf° for the gaseous molecules at 298 K, in kJ mol" , have stabilisation was accounted for in terms of quantum me- been taken from a computer-analyzed revision (8) of thermochemical data (9). However, to maintain continuity with chanical resonance, involving in the main the two equivalent 1 Kekule structures (4) and an empirical resonance energy of the older literature, the results are reported in kcal mol"* -1 1 kcal ^ 4.184 kJ. All the calculations have been carried out to 37.3 kcal mol"" was calculated as the difference between the 1 experimental energy of atomization of benzene and a value two decimal places and rounded off to one decimal place. calculated using bond energies JS(C—H), B{C—C), and AHa" is used to denote enthalpy of atomization, and for a E(C=C) derived from thermochemical data for paraffins and hydrocarbon, CmHn, olefins (5). To meet the requirement that the single valence bond structure used as reference should be a distorted AHfl°(CmHn) - mAHf°(C) + nAHf(H) ~ AH(°(CmHn) 1,3,5-cyclohexatriene structure in which al! the carbon-carbon (1) bonds are equal in length, 1.39 A, and not a structure with where Afff°(C) and AHf"(H) are the enthalpies of formation alternating long single bonds of 1.64 A and short double bonds of the carbon atom from graphite and the hydrogen atom from of 1.34 A, a "compressional energy" correction factor was H ,170.9 and 52.1 kcal mol"1, respectively (8). subsequently introduced (6). 2 Following Pauling and Sherman (5) the stabilization energy, The present article deals with the nature of this empirical SE, for benzene is given by the expression (i.e., experimental) resonance energy—how its magnitude depends upon the choice of reference molecules from which SE ° (benzene) - 6£

Volume 61 Number 3 March 1984 225 3) Substitute tie bond energies from step 1 in eqti. (2) and collect The Matching of Structural Elements In Reactants and like terms. SE then appears as a sum and difference of AHa" Products values for benzene, the paraffin(s) and the olefin{s} which is AH° for the particular reaction. Dewar and Schmeising (11) criticized this procedure on the grounds that there were energy contributions to SE arising

The calculations of SE using the bond energies derived from from the stabilizing influence of Cfip2—-Csp8 bonding in the the sets of molecules 1-10 in Table 2 are thus found to be cyclohexene that was not matched in the benzene and eyclo- equivalent to AH° for reactions 1-10 in Table 3 evaluated hexane, which would serve to diminish the value, from the ring directly as the difference between AHf for the product and strain in the cyclohexene, which wouid serve to enhance the reaetant species. value, and from hyperconjugation effects. To avoid these ir- The procedure introduced by Kistiakowsky et al. for the relevant energy contributions, they proposed that the hy- calculation of SE, namely taking the difference between AH ° drogenation heat of ethylene be taken as reference. This is for the hydiogenation of benzene to cyclohexane and three equivalent to evaluating SE as AH" for the reduction of times AH" for the hydrogenation of cyclohexene to cyclo- benzene by ethane. hexane, i.e., -49.8 - 3(-28.6) = 36.0 kcal rool-1 (3,10), is, in effect, the determination of SE as AH° for the reduction of benzene + 3CH —CH — cydohexane + benzene by cyclohexane, 3 3

i.e., reaction 3, Tabie 3. But this reaction also has mismatched benzene + 2 cyciohexane -* 3 cyelohexene bonding. The Cspa-—Csps bonds are not matched in the i.e., reaction 7, Table 3. products, nor are the various kinds of C—H bond (22).

Table 2. Values for the Bond Energies £(C—-H), E{C—C), and E(O=C> Obtained Using Different Sets of Reference Molecules, and the Corresponding Values of SE for Benzene in kcaf mol"1 at 298 K.

Reference Molecules" E(C—H)»

1) CH,. CHaCH3, CH^GHj A/A = 99,3 C - 3A/2 * 78.8 B - A = 140.6 64.2 2) CHaCH), CHjCHzCHs, C/2 - EIA = 98.6 3E/S~2C=B2.B B+E-2C= 143.2 48.4 3) CHaCHs, cyciohexara, CHfe=CHs! CIA - LIZA » 98.6 LIA ~ C/S = 82.8 B + t/0 - C « 143.3 48.4 4) CH* CH3CH=CH2 A/4 = 99.3 sum "D3/V2* 224.8 48.1

5) CH,, CH3CH3, (CHj>2C=CHCH3 A/4 = 99.3 C - 3A/2 = 78.8 t+2A-3C= 156.3 17.0 6} CH4, CHaCHa, (CHalsC^Cr^ A/4 = 99.3 C - 3/V2 * 78.8 J + 3A ~ AC = 160.5 4.4 7) iCHfl], cyctohexane, cyctohexene A/A = 99.3 L/6 - A/2 " 81.5 K - 5N/6 = 147.4 35.8 A/4 = 99.3 8) £CH,], CHaCH3. frans-CH3CH==CHCHa 0-3.4/3 = 78.8 H+ A-2C= 151.5 31.7 A/A = 99.3 9) [CH,], CMs=CHj, trans

* The reference molecules In square Drac&eis nave been added & order to solve tha simultaneous equations for ma bond energies. Their enthalpies at atamluttlon do not, however, appear in the final eiprssston for SE. . 6 The capfta! Setters denote enBiaipjas at alomiiatlon as follows: A. CK.: S. Crfe-=CHS; C, CH3CH3; O. CUJCH^CKJ; E, CHjCHjC+fe; F, fiamM>ls=CH~CM==Crk G, 90° CH^^CH— CH=CHS; K Mn&CHaCH='CHCH3: /, (CHsfeC^CHCHa; J, (CHalaC^CICHalj; K, cyeloWiane: and L. cyclohaxane,

Table 3. Various Reactions Whose AH° Values, in kcal mof~\ al 298 K can be Taken as a Measure of the Stabilization Energy Oi Benzene, SE, Together with Their Specification as to Whether There is Matching between the C—H, C—C and C=C Structural Elements In Reactants and Products. *

C—H Structural Elements c-•C and C=€ Structural Elements

Reaction AH" C[4}H, C[4]H3 C{4]Hz Cj3]H2 C|3]H C{4j-C[4] C[4]-C[3] C[3]-C[3] C[3]-C[3]

1) ben;ene + 8CHj • •-• 64.2 ± 1.7 no no no no no no yes SCHsCHa "1" SCH^^^CH? (24:0) (0:16) (0:12) (6:0) (0:3) (3:0) (3:3) 2) benzene +. 9CHaCH3 — 46.5 ± 1.8 no no no no no no yes 6CH3CH2CH3 + XH2—CH^" (54:36) (0:12) (0:12) (6:0] (9:12) (3:0) (3:3) 3| Benzene + 3CB3CH3 -" 48.4 ± 1.2 no no no no no no yes cyclohexane + 3CHj=GH? (18:0) (0:12] (0:12) (6:0) (3:6) (3:0) (3:3) 4) benzene + 3CH, — 48.1 ±0.7 no no no no no no yes 3CH3CH—"CHS (12:0) (0:9) (0:6) (6:3) (0:3] 3:0) (3:3) 5) benzene + eCHjCHs •-•* 17.0 ± 1.1 no no no no no no yes 3CH4 + 3(CH3)2C=CHCHa (0:12] (36:27] (6:3] (6:0) (0:9) (3:0) (3:3) 6) benzene + 9CH3CHa -* 4,4 ± 1.7 no no no no no no yes i:;: 6Cri4 ~r 3(CH3)jC' G(Cn3)2 (0:24) (54:38) (6:0) (9:0] (0:12] (3:0) (3:3) 7) benzene + 2 cyclohexane ~* 35.8 ± 0,6 yes yes no no no yes 3 cyclohexene" (24:24) (6:6) (12:9) (0:6) (3:0) (3:3] 8) benzene + 3CH3CH3 -- 31.7 ±0.6 yes yes no no no yes 3 (faos-CHaCr+=CHCH3'' (18:18) (6:6] (3:0] (0:6] (3:0) (3:3) 9) benzene + 3CH2-=CHS — 21.6±1.5 yes yes yes yes 3 frar)s-CHs='CH—CH=^CHs (12:12] (6:6) (3:3) (3:3) 10] benzene + SCHj^CH; -• 43.0 ± 3.6 yes yes yes yes (12:12) (6:6) (3:3) (3:31

a C{4] and Cj3] flenole carbon aioms to which four and three other aloms, respectively, are bonded. CHiH,. C[4]H3, C[«|Hj, C|3]Hj. and C|3jH dsnole a carbon-fiydrogBn bond In

CH4and CH3—, -CH!—. =CHj and ==OH— groups, fespecl/vely. TtienumBers in parentheses lx:y) giue Ihetolal number of each ktnd of carttorMiydroBen Bond in DM reaetant (x) and producduci fyj moleculea. ° 7

benzene + 3(n + * 3nCB+iH2B+4 + 3CH3-=CH2.

= Correcting for ihe ring strain energy associated wl!h cyclohexene. 1.32 kcal mor1 (9). AW becomes 31.9 kcai' 0 With cls-2-ttiitene, wfileh is 1.05 kcal ™r' less stable (fl|, AH" becomes 34.S kcat mor1.

226 Journal of Chemical Education In fact the very wide range of SE values in the tablea is due Reactions 9 and 10 beiong to a special subgroup called to contributions to the reaction enthalpy arising from struc- homodesmotic (23) to emphasize the sameness in the char- tural changes other than those responsible for the aromatic acter of the bonding in reactants and products over and above stabilization in the benzene. To trace these changes, the the equality in the number of bonds of each formal type, i.e., bonding state of the carbon has to be taken into account, C[4] there are equal numbers of each kind of carbon-carbon tetrahedral and C[3j trigonal (so' there are C[4]—C[4], bond—C[4]—C[4], C[4]—C[3j, C[3]—0(3] and C[3j 2 C[4]—C[3j and C[3]—C|3] single bonds ), as well as the =C[3]-—and equal numbers of C[4] and C[3) atoms with one, number and land of nearest neighbor atoms around each kind two, and three hydrogen atoms attached. Since homodesmotic of carbon. Nearest neighbor bonding can be specified conve- reactions minimize energy contributions arising from changes niently in terms of the number of bonded hydrogens. in the bonding state of the carbon and changes in the bonding The results of this analysis are set out in Table 3, where it of the hydrogen they are the reactions of choice for the eval- can be seen that the majority of the reactions fall into one of uation of stabilization energies from thermochemical data, three categories. In reactions 1-6 only the C=C bonds are e.g., for polycyclic benzenoid hydrocarbons and other cyclic matched; in reactions 7 and 8 the C—H bonds are also conjugated hydrocarbons (24). Similar reactions, in which matched; and in reactions 9 and 10 the C—C bonds are nitrogen-carbon bonds are matched according to the bonding matched as well. state of the nitrogen together with the number of hydrogen atoms attached to each kind of nitrogen atom, can be set up Closer examination shows that finer distinctions can be for the evaluation of stabilization energies for aromatic ni- made. Although the mismatch in the C—C bonding is the trogen heterocycles, e.g., pyridine, pyrrole, and porphtne (25). same in reactions 1 and 2, the mismatch in the C—H bonding The stabilization of aliphalic acyl compounds is quite different and the SE values differ by 16 kcal mol"1. In reactions 1,4, 5,6, in which the ethylene is unsubstituted, mono-, tri- and tetra-metbyl substituted, respectively, the mismatch is different in both the C—H and C—C bonding, with respect to reference molecules containing C=O and 1 and at the extremes the SE values differ by 60 kcal mol"" . On C—-X bonds, and compounds of the type the other hand, in reactions 7 and 8, not only is the C—H bonding matched, but the mismatch in the C—C bonding is the same. If AH0 for reaction 7, which is the reaction that underlies the procedure of Kistiakowsky et al. is corrected for with respect to molecules containing O^, C—X, and C—Y the ring strain energy of the cyclohexene, it becomes 31.9 kcal bonds, can also be treated in the same way. mol"1, which is identical to the value for reaction 8 within Literature Cited experimental uncertainty. Although in their entirety the (1) Stohmann.F.A.C..J. Prakt.Chemw.il, 13,538{18S0|;43,21 (1891):45.475US92); structures of the reactants and products in these reactions are 48,447 (1893J. For a discussion (,/thia workseeHeinridi.F., "Theories of Organic very different, this very close agreement is in accord with more Cheiniatxy," (translated by Johanaon, Tr R, amS Hahn, t>. A.}, John Wiley and Sons, Ne»Yotk, 1323. pp. 23-2B. recent assignments of bond energy terms which take into ac- (2) Kiatiakonsky, G. B., Ruhoff, 2, R., Smith, H. A., and Vaughan, W. E.,J. Amer. Ckem. count the bonding state of the carbon and the number and Sac, 68,137(1936). kind of nearest neighbor atoms (9,13,14), and with corre- (3) Kistiakowsky, ti. B, Ruhoff, J. R.. Smith, H, A., and Vangfuin, W. E., J. Amer. Chem. sponding group additivity schemes (15,16). Soc, 58, 146 (1336). <4) Pauling, L., and Whelond, G. W., J. Chem. Phya., 1,362 (1933). In matching the C—-C bonding in reaction 9, C[3]—C[3] is (5) Pauling, L., and Sherman, J..J. CAem./>ft}s.. 1.6fl6 (1933). (6) Coulaon, C. A., and Altaian, S. L, Trom. Faraday S™., 48,293 (1952!. identified with the central bond in the planar trans-1,3-bu- (7) See, for example, the following papers and references therein: (a) Dewar, M. S., and tadiene molecule (14). But this amounts to assessing the sta- de Llano, C, J. Amer. Chsm. Stic, 9i, 789 (1939); (hi Hess. Jr., B. A., and Schaad, L. A, J. Amer. Chem, Soc., 93,2413 (1971); (c)Aihara. J-i, J. Amer. Chan. Son., 98. bilization in benzene relative to three times whatever the 2750 (1976); id) (lutman I., Milun, M.. and Trinajstjc, N., J- Amer. Chem. Sue, 98, stabilization is in the aliphatic diene. It has been argued, 1692 (1977): (e) Bauki, N. I., Welsh™, T. L., CessacJ., and Holloway, R. I*, J. Amer. rather convincingly, that the stabilization is quite small, at Chem. Soc, 180, 6920 (1978); (f) Haddon, R. C J. Amer. Chem. Soc., 101, !722 x !I979);(B)KDl]n!af,H.,J.^mer.Cftera.Soc., 10I,4332a979);(h)HEindon,W.C., most only a few kcal mol~ (17), and recent ab initio calcula- Isr.J.Chem., 20.270(1980). tions strengthen the case (18). There is no way it can be (8) Pedley, j. B., and Rylance. J., "Suaaex-N.P.L. Computer Analysed Thermochflmical Data: Organic and OEganoraetailic Compounds," Univ. of Susses, 1B77. evaluated from therraochemical measurements, because there (9) Cos, J. D., and Pilcher, C, "ThGrsnocheroiatry of Organic and OrganomeUlhc Com- is no appropriate stable molecule with a C[3]~C[3] bond to pounda," Academii; Press, New York, 1970. (10) Paiiling, L., "The Nature of the Chemical Bond," 1st eil..C

Volume 61 Number 3 March 1984 227 edited by: FRANK S. QUIRING Clayton High School o place for cheml/t/ Clayton, Missouri 83105

Analytical Chemistry

Michael D. Seymour Hope College, Holland, Ml 49423

It is important to realize that in the practice of his or her which the sampie was collected, stored, and treated. This profession the analytical chemist uses a wide variety of ex- overall understanding of the problem and the sample is a perimental procedures. The field of chemistry has tradition- necessary prerequisite for choosing a measurement process ally been divided into the major disciplines of analytical, in- which will provide both the desired information and the re- organic, organic, physical, and biochemistry. Today, however, quired level of reliability in terms of accuracy and preci- there is a large amount of overlap among the various disci- sion. plines as seen by job descriptions for chemists in areas such Choice of the optimum experimental procedure is a decision as physical-organic, environmental, analytical, bio-inorganic, for which the analytical chemist is uniquely qualified. The organometallic, as well as medicinal, clinical, and polymer wide variety of problems encountered by the analytical chemistry. In view of such a muitidiseiplinary marketplace, chemist requires the use of methods which range from tradi- it should be understood that an effort to describe the activities tional wet chemistry to modern instrumentation. Compendia of the analytical chemist is meant only to be suggestive and of analytical methods provide ideas as to what techniques may by no means limiting. be most applicable, but it is up to the analytical chemist to organize creatively the appropriate methods into a procedure What is Analytical Chemistry? which works well for the samples at hand. The method selec- Analytical chemistry basically deals with the qualitative tion and experimental design must be based on previous ex- and quantitative identification, characterization, and mea- perience, general knowledge of the chemical reactions in- surement of the chemical species present in a sample. The volved, the desired accuracy and precision of the data, and the measurement process can range from standard techniques for suitability of various instrumental and wet chemistry proce- routine quality control to state-of-the-art techniques used for dures. In situations where more than one type of procedure fundamental studies. However, regardless of the measure- is capable of providing the requisite precision and accuracy, ments made, the actual experimental determination of a given the analytical chemist must use cost/benefit considerations chemical species is only one aspect of a much more compre- in choosing the least expensive way of obtaining the desired hensive analytical procedure which takes into account: information. For example, the benefit associated with an expensive, highly accurate, and very precise quantitative anal- 1) definition of the problem and the manner in which chemical ysis of drinking water for a component which may affect analysis wiii be relevant to its soiution, human health is worth the cost, but the benefit of an equally 2) identification of the appropriate chemical species to be mea- expensive, accurate, and precise analysis for a component sured, which only imparts a slight odor to the water may not justify 3) collection and preliminary treatment of the sampie, the cost when a less expensive, less accurate method can 4) selection of a suitable measurement technique with respect to provide the required information. Analyses which are more species concentration, accuracy, precision, cost and time, accurate than the situation warrants can be costly and 5) separation of the desired species if interfering components are wasteful in both time and resources; while, on the other hand, present, analyses that lack the necessary accuracy are of little use. 6) measurement of the concentration of the species 7) evaluation of the data, and 8) communication of the results. Other factors which enter into the cost/benefit consideration are the time required for a single determination and the A closer look at each of these individual operations will pro- total number of determinations to be performed. The overall vide an idea of the diversity and challenges involved with the impact of these two factors is often reflected in the choice problem-solving aspect of analytical chemistry. between wet chemistry and instrumental procedures. While The first three of the above operations will often not be wet chemistry procedures such as titrations and gravimetric under direct control of the analytical chemist, but will be the methods offer low cost with good accuracy and precision for responsibility of the person, or client, requesting the chemical high concentrations of selected components, they may be analysis. This, however, does not mean that these operations lengthy if many samples are analyzed. Instrumental proce- can be neglected. The analytical chemist should obtain as dures, on the other hand, are generally more expensive in much information as possible about the client's problem, the terms of initial cost, offer lower detection limits with some loss way in which the chemical data are to be used and interpreted, in precision, and require less analysis time per sample, which the genera! composition of the sampie, and the manner in can make them cost effective for large numbers of samples. The experienced analytical chemist will realize that the proper use of both instrumental and wet chemistry methods com- This feature surveys the diversified careers which are available to plement each other and will make extensive use of both. chemists or which require some chemical training. We are alt "career Since most samples are really complex mixtures they often consultants to some degree. This feature may supply some new insights as to what is available. require some type of clean-up procedure in order to isolate effectively the component of interest, or analyte, from other

228 Journal of Chemical Education components which may interfere in the analysis. In order to Career Planning avoid time, expense, and possible loss of any anaiyte due to Students interested in analytical chemistry should realize lengthy isolation procedures the analytical chemist should that the discipline is both applied and fundamental in nature. develop efficient separation schemes. The separation may The applied concept uses established procedures to obtain require the combination of several standard methods into a information about a specific problem, while the fundamental unique procedure for the matrix of interest. For example, the concept is concerned with overcoming problems associated vanadium content in a new alloy may be critical to its physical with the development of new tools and techniques with which properties. While methods for determining vanadium exist, to better investigate the physical and chemicai properties of none of them may be suitable for the new alloy. Thus, the materials. The new knowledge which is obtained as a result analytical chemist would need to develop a procedure which of fundamental studies has the potential to improve the ap- would be suitable for this new matrix. plied aspects of the discipline. While the applied studies are After the appropriate collection and separation steps have generally found in industrial settings and the fundamental been taken, it is the measurement process used in the labo- • studies in academic settings, there are no fixed dividing lines ratory which finally provides data on the anaiyte concentra- and both applied and fundamental studies are carried out in tion. The quality of the experimental data will ultimately both settings. Regardless of the setting or the type of work,. depend on the ability of the person performing the measure- the analytical chemist will be presented with challenging ments. In many cases the data will not be obtained by the opportunities to investigate new and interesting areas, to analytical chemist, but rafter by personnel trained specifically overcome unforeseen technical and chemical difficulties, and for that purpose. These technical personnel, or analysts, need to gather original information in response to unique questions. not be. concerned about the overall scope of the problem, but With the rapid development of computer technology, op- should focus on the quality of data, ensuring that it is acquired portunities for analytical chemists promise to be even more with the best possible accuracy and precision inherent to the exciting and demanding. In a special report on the future of method. The position of analyst is one frequently filled by analytical chemistry1, Thomas Isenbour comments on the bachelor degree chemists, since a general background in future of computers in analytical chemistry, "It looks great. chemistry is needed to learn effectively and understand the The table has been set for a feast of new analytical chem- specific experimental procedures used in any given laboratory. istry." Although the job of analyst is not aa invoived as that of the analytical chemist, it is very demanding and requires a high To prepare for a career as an analytical chemist or an ana- degree of proficiency. lyst, students should take as much math, chemistry, and physics as possible in high school. At the college level the After the data have been acquired they must be converted student should take courses required for a chemistry major, to a form which is relevant to the problem, such as absorbance as well as courses in statistics, electronics, and computer readings being converted to the weight percent of anaiyte science. Courses which.deal specifically with analytical present in the original material. For many routine experiments chemistry, instrumentation, or separations should be taken acquisition of the raw data and conversion to meaningful re: if they are not included in the chemistry major requirement. sulis is automatically carried out by computers, but the fact Independent research should be part of the student's program that a result is calculated to 12 digits does not mean that it is if it is at all possible, because it is through this type of activity correct. The analytical chemist should have some intuitive, that the student learns how to define a problem and to develop common sense feeling for the quality of the data based on past a systematic approach for obtaining the data needed to ad- experiences. Thus, he or she should be able to identify those dress the problem. While the formal training offered at the results which may indicate erroneous procedures. In addition undergraduate level cannot turn out students ready to attack to calculating the final result, it is essential that the analytical every type of problem (and is not intended to), it can provide chemist calculate the reliability of the result in terms of pre- students with both a sound background of fundamentals on cision and accuracy. The random errors associated with pre- which to base decisions and a confidence in one's ability to cision will tend to cancel one another when a large number of gather accurate, reproducible data. measurements are made, but determinate errors such as operator, instrumental, or procedural bias which affect accuracy Education at the undergraduate level will, in most cases, do not cancel and will offset the experimental results from the be appropriate for a student to seek employment as a tech- true results. By proper use of statistical procedures the ana- nician, tar students who wish to seek positions with a broader lytical chemist can determine the extent of random and de- range of reponsibilities and to develop self-directed research terminate errors and consequently design or re-design ex- programs it will be necessary to obtain a master's or, prefer- perimental procedures which maintain the required accuracy ably, a doctoral degree. Many graduate programs are struc- and precision. The degree of uncertainty indicated by the tured such that the student can proceed directly from the accuracy and precision must also be communicated to the bachelor's degree to the PhD without earning a separate client. This allows the client to arrive at an interpretation of master's degree. In graduate school, the student will generally the data which is consistent with the experimental procedures take courses which have a strong emphasis on analytical and which also takes into account any limitations associated methods, such as separations, spectroscopy, electrochemistry, with the data. electronics, or solution equilibria, although many other spe- cialized courses are offered. The PhD is a research degree, so The analytical chemist must oversee a large number of that a major portion of the student's activity will be involved operations in the process of performing a chemicai analysis. with a unique research project under the direction of a pro- The task of selecting the best procedure for a given analysis fessor who serves as the student's mentor during the course can be compared to selecting the best path through a maze. of the studies. Students who are thinking about attending In selecting a path through a maze, there are many directions graduate school should also be aware that there are a rea- in which to proceed and one may encounter many wrong turns sonable number of graduate teaching aesistaniships available and dead ends. The task however becomes much easier if one which pay stipends. has an overview of the entire maze and clearly knows in which direction to proceed to find the end. Similarly, for a chemical Upon completion of the PhD the analytical chemist may analysis, there are many procedures which may be used to proceed into a variety of governmental, industrial, or academic obtain the desired information, but selection of the best pro- positions. An extensive survey of salaries for chemists is given cedure becomes easier when the problem is clearly defined and in the July 11,1983 issue of Chemical and Engineering News. the requirements for the data well established. 1 Isenhour, Thomas, Ana!, Chem., 55,824 (1983).

Volume 61 Number 3 March 1984 229 While the job descriptions will vary greatly, the activities of provide the best answer to these questions, the analytical the analytical chemist most often will involve answering chemist must have a critical attitude toward the techniques questions which deal with various aspects of the overall ana- and procedures which are used and the results which are ob- lytical procedure outlined at the beginning of the article. To tained.

report of the polymer core cour/e committee

Inclusion of Polymer Topics into Undergraduate Inorganic Chemistry Courses

Inorganic Core Course Committee1

Inorganic Core Content Related to Polymer Science c) Poiymeric solid state structures: oxides, chlorides, sulfides, Inorganic chemistry core courses typically focus on the re- earbon (graphite and diamond). d) Important polymers (but not necessarily in commerce): alumi- lationships of structure and reactivity in compounds of all the num hydride/alkoxide, (SO3)r, metal alkyb, SbF6, sulfur, elements except catenated carbon (organic chemistry). In- phosphorus. cluded as integral parts of these courses are discussions of e) Concepts useful to the understanding of polymerization reac- polymers and polymeric structures since many inorganic tions: structure and chemistry of organometallics, metal car- substances lack discrete molecular species and have chemistry bonyE chemistry, and olefin complexes. inextricably related to their extended structures. Notable examples of these substances would be metals, metal salts, These topics are, in fact, considered in current inorganic oxides, silicates, nitrides, etc. These and even the more clas- texts in enough length and detail to please polymer scientists. sical inorganic polymers such as siloxanes, boranes, stlanes, Where only one course of truly inorganic chemistry is in the phosphazenes, polyphosphates, etc. often do not have isolable curriculum it is impossible for it to include of all polymer monomeric units typical of classical organic polymers, so the science concerns. If the structure and reactivity relationships actual "polymer science" content in the core courses has among the elements aTe faithfully portrayed, however, the somewhat different format. Practical applications of poly- interests of polymer scientists, biochemists, biologists, solid meric inorganic substances likewise extend beyond the usua! state chemists, physical chemists and analysts, engineers, and purview of polymer chemistry concerns, which are largely nuclear scientists, etc. are being well served. When possible, organic in nature. It is safe to conclude, nevertheless, that no an additional course can provide for study of organometalHc study of inorganic chemistry is intelligible without an un- chemistry in a depth more suited to polymer science inter- derstanding of its intrinsically "polymeric" structural con- ests. tent. Resource Information and Illustrations It does seem appropriate that chemistry of the more tra- In order to stimulate student interest and emphasize real ditional inorganic polymers be included in the core along with world relationships of inorganic chemistry and polymer discussions of mechanisms and syntheses of substances ca- science, it would be extremely valuable to have, for classroom pable of forming linear or branched polymers. Additionally, use, samples of actual commercial materials employing inor- the chemistry of inorganic species that catalyze organic ganic polymers. Some materials like (SN)*, boron-fiber-re- polymerizations or the synthesis of important monomers inforced plastic, ferrocene, and polycarborane polymers would should be presented. A listing of important inorganic topics be uniquely and corapeliingly illustrative but are not readily of current interest to polymer science would thus reasonably available. Other materials, such as zeolites, silicones, moly- include: suifide, are available at retail stores. The problems and opportunities related to obtaining these types of illustrative a) Notable linear and branched polymers: silicones, phospharenes, polysulfides, f SN),, boraaenes, poly phosphates, silicates. materials are considered in another, associated report that was b) Catalytic systems important to condensation processes (if or- published on page 161 of the February 1984 issue of THIS ganic monomers: Ziegler catalysts, organolithium reagents, or- JOURNAL. ganometallk catalysts, and anchored metal catalysts. Other information in this section is provided as examples of resource material for students that: {a) helps them to appreciate the relationships of inorganic chemistry and polymer 1 The inorganic Core Course Committee consists of: science; {b) illustrates theory and concept; and (c) points to Norman E. Milter, Chair, University of South Dakota, Vermillion, SD emerging areas of research and application. 57069 John J. Fortman, Assistant Chair, Wright State University, Dayton, Ohio Commercial Materials 45435 The relationship of inorganic materials with polymer Ronald D. Archer, University of Massachusetts, Amherst, MA 01003 science extends to auxiliary uses such as fillers, colorants, Martel Zeldttt, Indiana University-Purdue University In Indianapolis, Indianapolis. IN 08453 opacifiers, antistatic agents, preservatives, processing aids, B. Peter Block, Pennwalt Corp., King of Prussia, PA and reinforcing agents. The table is a partial listing of trade Robert Brasled, University of Minnesota, Minneapolis, MN 55455 and brand names of inorganic materials utilized in the poly- John E. Sheats, Rider College, Lawrenceville, NJ 08648 mer industry.

230 Journal of Chemical Education List of Inorganic Compounds Utilized in the Polymer Industry Homogeneous metal complex catalysts are known which Trade or selectively promote useful reactions under mild conditions. Brand Name Product Manufacturer Such reactions include hydrocarboxylation, linear oiigomer- ization, cyclooligomerization, hydroformyiation, decarbox- Acryiacon Fibrous-glass reinforced Rexal! Chemical Company ylation, and hydrogenation, Through attachment of a homo- polymers geneous catalyst to a cross-Jinked polymer, the catalyst is Albacar Calcium carbonate filler Pfizer Corporation made "heterogeneous" with respect to the specific reaction Abslbronz Wetground muscovite Franklin Mineral Prod. Co. environment. Many transition metal complexes have been mica attached to swellable styrene-divinyibenzene resins. Alsliate Clays Freeport Kaolin Co. Atornite Calcium carbonate Thompson, Weinman & Co. The wider topic of polymer supports in organic synthesis Azdel Fibrous-glass reinforced Generic is covered by a continuing column (since vol. 4, 1977) by ABS sheet Charles Pittman in Polymer News, parden Kaolin c|ay Muber, J. M,, Corp, Bondstrand Filament wound liber glass Ameron Corrosion Control Polymers Modified or Formed by Coordination reinforced plastic Div. Polymers involving coordination at metal sites have been Boroflt Boron filaments Texaco Corporation technologically important before recorded history. For in- Cab-O-Sil Colioida! silica Cabot Corporation Calwhlte Calcturh cartionate Georgia Marble Co. stance, the tanning of leather depends on the coordination of Camel-Carb Calcium carbonate Harry T. Campbell Sons' Corp. metal ions with the proteins which make up the hide. These Carboioy Cemented carbides General Electric Co. protein-metal ion complexes resist bacteria! attack, wear, and Carbospheres Hollow carbon spheres Versar, Inc. weathering which befall nontanned animal skins. Similarly, Celite Dlatomite fillet Johns-Manvllle Corp. metals bound to other natural polymers, including proteins, Celramtc Glass nodules Pittsburgh Coming Corp. affect numerous enzymatic and membrane interactions. Dlcafite Dlatomaceous earth Dlcafite Grefco, inc. Metals can be coordinated with organic ligands to form a Eccospheres Hollow glass spheres Emerson a Cummlngs, Inc. polymer or to form a coordination complex within an already EH Cabot Corporation Carbon black formed polymer. The correlation of product structure with Flberglas Fibrous glass Owens-Corning Fiberglas Corp. property is more comprehend!bie when the coordination Firmex Carbon black Columbian Carbon Co. polymer is designed to contain a repeat unit with one metal Flaksglas Glass flakes for Owens-Corning Fiberglass ion per unit. Even so, there exists a larger number of synthe- reinforcement Corp. sized coordination polymers for which the exact structure is Ffuorobestos Asbestos-Teflon Raybestos Manhattan, Inc. unknown and probably varies within a single polymer composite chain. Gama-Sperse Calcium carbonate Georgia Marble Co. Bailar has listed a number of principles in designing coor- Garan Fibrous-glass roving Johns-Manvllte Corporation dination polymers (1-3): {1) little flexibility is imparted by Glaskyd Giass-reinforced alkyd American Cyanamld Co, resin the metal ion in its immediate environment, so the flexibility Hi-Sit Amorphous silica PPG Corporation must arise from the organic moiety; (2) metal ions only sta- Horse Head Zinc oxide pigments New Jersey Zinc Co. bilize ligands in their immediate vicinity, thus the cheiates Hytirocal Gypsum U. S. Gypsum Co. should be strong and close to the metal atom; (3) thermal, Kadox Zinc oxide New Jersey Zinc Company oxidative, and hydrolyttc stability are not directly related, Kaiite Precipitated calcium Diamond Alkali Company thus, polymers must be designed specifically for the properties carbonate desired; (4) metal-ligand bonds have enough ionic character Kalmac Calcium carbonate Georgia MarBle Company to permit them to rearrange more readily than typical "organic Kaofill Coating and filter ciay Ttilele Kaolin Company bonds," (5) flexibility increases as the covalent nature of the Kosmos Carbon biack United Carbon Company metal-ligand bond increases; (6) coordination number and Kronos Titanium dioxide Kronos Titan stereochemistry of the metal ion determines polymer structure Ludox Colioldal silica du Pont de Nemours & Co. (such as square planar, linear, planar, or three-dimensional); Mlcronex Carbon blach Columbian Carbon Co. (7) complex formation is favored through use of pure reactants Miner Aluminum silicate filler American Nepheiine Corp. in stoichiometric amounts, MoguJ Carbon black Cabot Corporation Powminco Asbestos fibers Powhatan Mining Co. Polymers involving coordination can be prepared by a Q-Cel Inorganic hollow Phlladeiphiii Quart; Co. number of routes, the three most common being: (a) pre- microspheres formed metal complexes polymerized through functional Santocel Silica aerogel tillers Monsanto Co. groups, where the. actual polymer forming step may be a Sllaslic Silicons materials Dow Corning Corporation condensation or addition reaction, Sllastomer Sllicortes Midland Sllicones, Ud. Sifene Calcium silicate PPG Corporation Statsx Carbon back Columbian Carbon Co. Styraglas Fiber glass reinforced Dart Industries, Inc. H—-Q O—H polystyrene Suriyn lonomer resins du Pont de Nemours & Co. Thermax Carbon black Commercial Solvents Corp. Thomel Graphite filaments Union Carbide Corporation Ti-Pure Titanium dioxide pigments du Pont ife tumours & Co. Titano* Titanium dioxide pigments Titanium Pigment Corp. Vicron Fine calcium carbonate Pfizer Minerals, Pigments & Metals

Anchored Metal Catalysts One of the most active research areas in chemistry is the study of chemical reagents and catalysts supported on polymers. A majority of these materials can be considered or- ganometaliic polymers. A number of "anchored metal" catalysts offer advantages over "nonanchored" catalysis in terms of efficiency, selectivity, and separation.

Votume 61 Number 3 March 1984 231 (b) coordination of a metal ion by a polymer containing ehe- Capping the hydroxyl end groups with monofunctional groups lating groups, derived from triaikylchlorosilane or trialkylalkoxysilane stabilizes the polymers, and addition of trifunctional linking groups derived from alkyltrichlorosilane gives cross-linked silicones. Because of the ease of formation of six- and eight- membered rings, there are many "wasted loop" side reactions, but fortunately, cyclic siioxanes may be removed by distillation and reused in the feed. T I—5—CH , S K. N Silicone oligomers are used as lubricants and antifoaming agents. Bouncing putty is produced when polydimethylsii- oxanes with capped ends are heated with boric acid. Silicone oils are prepared in the presence of hexamethySdiailoxane which produces trimethylsiloxyS capped ends, The viscosity and (c) polymer formation via coordination reactionso whicf siliconhe oils is controlled by the ratio of hexamethyidisi- are condensation-type reactions loxane to the dimethyldimethoxysilane used. Since polymerization of alkoxy- or chlorosilanes takes place in the presence of water, one-package systems are used as room temperature curing (vulcanizing) silicone elastomers, Linear silicones may also be cured by free radical reactions. Cross-linking is also promoted by bubbling oxygen through silicone solutions in order to oxidize the alkyl groups and thus form oxygen linkages between chains. HA—Il—AH + M+! ^C -(-A—R—A—St-J- The characteristic resistance of silicones to degradation at elevated temperatures is related to the siloxane backbone. The lubricity and water repellancy are related to the pendant HA—S—AH +M—X -f-A—B- iyophilic alkyl groups which encase the backbone. M Phosphazene or Phosphonltrilic Hailde Polymers 8" Phosphazenes are very important phosphorus-containing Condensation polymers of the latter type which involvinorganiec polymers. Three types of polymers based on the organometallic halides (or another organometailic moietyphosphazen of e structure have been developed: linear, cyclo- high polarity) and polyfunctional, potentially aniontc Lewilinears, and cross-linked cyclomatrix. bases can be considered extensions of classic organicLo conw glas- s transition temperatures, TB's, for most poly- densations. phosphazenes indicate low barriers to internal rotation and potential for elastomer applications. In fact, theoretical calculations based on a rotational isomeric model assuming lo- C!- •Cl + K~NH, calized TT-bonding predict the lowest (-400 cal/mole repeating unit) known polymer barrier to rotation for the skeletal bonds -f-C—R—C—N H—N- for poly(difluorophosphazene) (5). Condenaation Polymer From a practical point of view polyphosphazenes are usually soft just above the lowest phase transition, so that compression molding of films can be carried out. This suggests, that the CI—M-~a + K—-MS, -f-M- lower transition of the two first-order transitions usually observed for organo-substituted phosphazenes represents the Condensation upper temperature for most useful engineering applications. Organoroetallie Polymer Polyphosphazenes are described in greater detail in references ,n fact, research in this area was catalyzed by observatio(6) annd (7> tha. t the organometallic halides behave like organic acid chlorideHeterogeneouss Polymerization Catalysts (3,4). Prior to 1950, the only commercial polymer of ethylene was Potysiloxanes a highly branched polymer called high-pressure polyethylene (extremely high pressures were used in the polymerization Lack of strong single bonds between elements other than process). A technique for making a linear polyethylene at low carbon has limited the interest in catenated inorganic poly- pressure was discovered by Karl Ziegler in the early 1950's. mers. Linkage between dissimilar atoms is stronger, for ex- Ziegler prepared high-density polyethylene by polymerizing ample Si—C (58 kcal/mole) and S>—0 (89 kcal/mole) bonds ethylene at low pressure and ambient temperatures using are much stronger than Si—Si (30 kcal/mole) bonds, making mixtures of triethylaluminum and titanium tetrachloride. heteroatom backbone polymers inherently more stable. Im- Giulio Natta used these complex coordination catalysts, now portant classes of commercial polymers of this type are those known as Ziegler-Natta catalysts, to produce crystalline with —Si—O— linkages that are the bases of the diverse polypropylene and to study stereoregular polymerization of technologies of glass, cement, and ceramics dating to antiq- olefins. Because of these remarkable contributions to polymer uity, and more recently to poiysiloxanes pr silieones (a mis- science, Ziegler and Natta were honored by the Nobel prize nomer arising from a ketone formality proposed in Kipping'a in Chemistry in 1963. workofthel920's). In general, a Ziegler-Natta catalyst may be described as a By reducing functionality of silicon to two by organic sub- combination of a transition metal compound from groups IV stitution, the spontaneous condensation of silanol groups is to VIII and an organometallic compound of a metal from used to advantage to make a host of commercially attractive groups I to III of the periodic table. It is customary to refer to silicone polymers: the transition metal compound such as TiCLj, as the catalyst, and the organometallic compound, such as diethylahiminum -i H,O chloride, as the cocatalyst. n[RsSi(OH),J S -8n HCI Several exchange reactions between catalyst and cocatalyst

232 Journal of Chemical Education take place, and some of the Ti(IV) is reduced to Ti(III). It is ganotin compounds. Certain metal complexes are exquisitely customary to use the purple, a or 5 forms, rather than the specific catalysts, so metal-containing polymers might afford brown, {$ crystalline form, of TiCla as the catalyst for the this specificity along with selective stereoregulation imposed production of atereoregular polymers. Both the extent of by constraints of the polymer chain. stereoregularity and the rate of polymerization are increased More recent research with conducting polymer films on by the addition of triethylamine. Thus, at least 98% of the silicon, polymetallophthalocyanines, polyacetylene, and (W)x isotatic polymer is produced when propylene ia polymerized promise a future in lightweight batteries, better solar cells, in the presence of triethylamine, 7-titanium (Ul)chloride, and conducting fibers, etc, as well as a better understanding of the diethylaluminum chloride. chemical physics of conduction theory. It is not clear just It is generally agreed that a monomer molecule which applications will prove commercially successful, but it is clear that the potential is enormous, in view of the almost H limitless variety of metal-containing polymers and the esca- lating need for specialty materials.

is inserted between the titanium atom and the proximal car- Literature Cited bon atom in the growing chain, and that this propagation re- (I) BaiSar. J. C, "Preparative Inorganic Reactions," Jolly, W., (Editor), Interscience Pubs., action takes place on the catalyst surface at sites activated by New York, 19B4, Vol. 1. (21 Bailar, J. C. "Organometallic Polymers," Carraher, €., Sheata, J. and Pitttnaii, C, the ethyi groups of the cocatalyst. Recent discussiona of (Editors), Academic PtesB. Now York, 1978, Chop. 31. mechanisms can he found in references (8) and (9). (5) CarrahiT, C..J. CHKM. EDUC., 58(11), 921 (I98W- HI Carraher. C, "lnterfaeial Synthesis. Vol. II Technology and Applications," Mdlich. F. Most vinyl monomers with Ziegler-Natta catalysts poly- and Carrahei, C, {Editors), Marcel Dckliet, New York, 1978. merize to give polymers emphasizing the isotactic form. The (51 Alleoek, H,, Inorganic Chem.,5.1320 (1966). (6) AHeoek, R, "Phosphorus Nitrogen Compounds," Academic Press, New York, 1972, degree of stereoregulation appears to be dependent on the (7) Singler, E. and Hagnanez, G.. "Organometalljc Polymers," Carraher, C, Sbeate, J. and amount of exposure of the active site; the more exposed the Pittman, C, {Editors), Academic Prera, Nsw York, 1978. catalytic site, typically, the less is the isotactic fraction in the (8) Chien, ,3., "Coordination PoJymeriiwtioji," Academic Prem, New York, 1975, resulting chains. (9) Natta, G. and Danusso, F,, "Stereoregular Polymers and Stereosperific Polymerisation," Pergamon, Now York, 1967. The potential versatility is clearly demonstrated in the polymerization of conjugated dienes, such as 1,3-butadiene, where any of the four possible forms—isotactic 1,2; syndio- tactic 1,2; trans-1,4; and cis-l,4~-can be synthesized in relatively pure form using different Zieglei-Natta catalysis sys- Appendix: Questions for Inorganic Core Content tems. Closely Related to Polymer Science Stereoregular polymers are also produced utilizing a number of other organometallic and inorganic catalysts including 1. Contrast the structures in (a) HNO3 and (HPOaJj; (b) COa and Philips and Alfin catalyst-systems. (SiOs)*; (c) BC13 and (BeCIn),. 2. Sketch the structure of each of the following, showing empirical Solubility formula. (a) single chain silicate Many inorganic polymers become soluble only with ac- (b) double chain silicate companying degradation (this is particularly true for three- (e} sheet silicate dimensional networks such as sand and diamond). Even the 3. S2N2 slowly polymerizes without much change in erystaHinity. ostensibly more tractable organometallic polymers are soluble Suggest a reason and explain the interest i» the resulting in fewer solvents and to lesser extents within these solvents polymer. than classical organic polymers. While a few are soluble in 4. Show structures for diamond and graphite, and explain why typical solvents such as toluene and chloroform, most are ei- graphite is a conductor and diamond ia not. ther insoluble or soluble only in a few select dipolar aprotic 5. With chemical equations describe the synthesis of high polymers solvents and salt-dipolar solvent combinations. Even where of the type (NPRg)s. What is the critical step which allows for solubility appears to have been achieved, actual polymer in- high molecular weight (degree of polymerization)? tegrity in solution may be questioned. 6. List advantages and disadvantages for the inorganic potymer The poor solubilities of organometallic polymers are classes of silieones and phosphazenes, compared to organic probably due to a combination of related factors including (a) polymers. high cohesive (secondary bonding) forces between chains, (b) 7. Bonding of inorganic polymers is varied. For the following poly- the highly crystalline microstructure of a number of products, mers select the single (best) phrase which describes the and (c) a peculiar combination of bonding offered by the or- bonding. ganometallic polymers—a combination of both nonpolar Polymer Bonding Explanations (organic) and polar contributions. Attempts to achieve better solubility include (a) use of flexible and/or dissymmetric reagents, (b) copoiyrrterization using two metal-, with one (a) 1. Sheet structure with sigma- nonmetal-containing reactant(s) or one metal-, with two bonded network reinforced by r non-metal containing reactants, (c) use of model compounds bonding. (monomers) as a predictor of polymer solubility, and (d) ad- 2. Lewis acid-base bonded dition of a chain terminator to shorten the chain length. backbone (c) (SN), 3. Sigma framework enforced by d-p IT bonding. Applicability id) (SOa>, 4. Shared corners, edges, and/or Apart from pure science, the interest in polymers which faces of octahedra and tetrahedra. include metal atoms is related to the enormous and varied (e) 5. Chain structure with one- chemistry of the metals and the technologies that might be dimensional meta!-3ike developed around them. For instance, polymers with Cp^M deiocalization moieties (M = Pe, Ti, Zr, Hf) are reported to be stable to uv (BN), 6. Three-centered bonding in radiation; thus, polymers with such groups might impart to bridges outdoor paint better wearability relative to uv degradation. Similarly, polymers incorporating tin would be expected to 8. (a) Outline a mechanism for Ziegler-Natta polymerization of have antifungal and antibacterial resistance typical of or- ethylene, CH2=CH2, by heterogeneous Ti(III) catalyst.

Volume 61 Number 3 March 1984 233 surface —J'K^) Each Si surrounded by 4 oxygens and each oxygen •.p=C™»o; versus bonded to 2 saloons to form framework (quartz) (b) Why is this type of polymerisation significant? Multiple Choice. Weakness of Si=O is obviously a facilitating property. Circle single best answer for: 9. The heating of sulfur is a cpmpiex process. (a) Rings break primarily to form aggregates of S* chains. * (b) Rings break to form polymers witii radical ends. (c) Chains break to form Se rings. 4h • 4)» 4% (d) Two of the above are correct. 10. Molybdenum dtsulfide is a lubricant because it is (a) a viscous liquid from below room temperature to elevated in solid temperature. Be, being more electron deficient than B, forms halide bridged (b) a solid composed of microspheres when precipitated from polymers. solution. * (c) a tayer structured solid with weak interpiane bonding, (d) none of the above, 2>(a> repeat SiO3 unit 11. Oxygen, sulfur, nitrogen, and phosphorus form homo-catenated compounds, * (a) such as ozone, hydrazine, red phosphorus, and dithionite. (b) such as hydrogen peroxide and pyrophosphates. fc} such as the various ailotropes of nitrogen and phosphorus, (d) Two of ti:e above are correct. 12. For the transformations

L,Ni (1) + H* L3NiH* (2) + L 7 + L,NiH + CH1=CHi L,NiH* (3) amphibole minarats repeat Si,Ous'unit

+ (e) LaNiCH,CH, (4)';

(a) Species (2) and (4| are "lfi valence electron" complexes. (b) Species (1) and (3) are "16 valence electron" complexes. (c) Species (1) and (3) are "1.8 valence electron" complexes. * (d) Two of the above are correct. 13. Some solid metal chlorides have discrete molecular units as exemplified by (a) CdCl and Hg Cl . repeat 2 2 2 3 * (b) AtCl3andAuCl3. or Si5O5 (c) NaClandKCl. 3) Little change in positions of atoms must be responsible for small (d) none of the above. change ia crystallinity during polymerization, 14. Ferrocene, like benzene, (a) has 6 it electron six-membered rings. (b> is a colorless liquid. ^j—6 K|—A * (c) has aromatic character. —| A (d) Two of the above are correct. 15. Silicate, borate, or phosphate glasses fa) unlike organic vitreous materials have sharp melting points. * (b) differ structurally in that borate glasses have occasional planar triangular arrays of BO, as well as the EO4 tetra- Bond structures difficult to draw because SN unit is "odd" in hedra. electron number. jr-Molecular orbitals encompassing chain form (c) are preparable from giant molecule precursors SiC>2, B2O3, partly filled conduction bands. Polymer consequently has and P2O3. metal-like conduction and can be consideied a one-dimensional (d) cannot be made from melts of basic oxides and the oxides of metal. It has been used to store electrons in battery systems. silicon, boron, or phosphorus. 4) Diamond has each carbon tetiahedraily bonded to 4 others. The lattice is the zinc blende structure with O=Za^=S

fee of carbon with carbon (Possible) Answers. in every other (shaded) smaller cube. ft & 11—a-- •& Carbons at face centers and centered in smaller cubes (10 in number) form adamantane cage whose 3-fold axis is coincident with cube diagonal. •0-

Nitrogen forms N=0 double bonds about as stable as 2 single bonds fgpod IT -orbital energy match) but phosphorus does not. For phosphorus oxyanion acids polymeric structures are possible via I'-O-P bridges. Formally, a head-to-tail polymer of the double- adamaatane cage bonded monomer results.

234 Journal of Chemical Education Strictly organic substituenls like Ph or CHg are not accessible from chloropolyraer reactions. 8) Silicones (or polysiloxaiies) etc. V V"* and polyphosphazenes, Graphite forms bonded layers with little inter-plane bonding. Consequently, graphite is "slippery." Each carbon shares 1 double v bond and 2 single bonds with 3 other carbons and is thus (2 + 2)/3 = 1% bond order. The ?r orbitals form extensive MO's v which are like 2-dimensional metal band structures. Being partly have strong sigma-bonded backbones (with d-p * bonding in filled (1 ir electron per JT atomic orbital} the band is conductive phosphazenes) which impart thermal stability. Hydrophobic organic substituents (R = alkyl, aryl for siiaxanes; R « -O-alkyl, -O-aryl, or -NH R for phosphazenes) confer a kinetic hydrolytic 5) NH4CI + PC1S • stability to the polymersS . Depending on substituents and cross- linking, polymers range from oils to elastomers. cyclic structures separated; when highly purified (from cross- Phosphazenes are more susceptible to hydroiytie degradation but linking PCi&) the trimer thermally polymemes to can be prepared in seemingly limitless classes by substitution reactions on preformed (NPCls)X high polymer. Novel features include a bouncing putty (siloxane polymer) and \/ci surgical sutures which hydrolyze to harmless products (phos- 15000 phazenes with -NHjR moieties being ammo acids). 7} a(3); b(6i; c(S); d{2); e(4); f(I) The linear polymers so obtained are still soluble in organic solvents 8) {a) and a host of substituted polymers are possible, many with physical and chemical properties for practical use. 8)

RHK KHB (b) Polymer grows from Ti sile outward leading to strictly linear polymer with high molecular weight and higher stereoregu- (NPC1,), + NHJl larity than polymers derived by radical initiation. Steric constraints at Ti site require higher oleims to polymerize with stereoregularity (to give isotactic polypropylene, for example).

Institute for High School Chemistry Teachers

An Institute for High School Chemistry Teachers will be held July 6-16,1984 at San Jose State University, San Jose, California. The purpose of the Institute is to provide background in theory through lectures by Ronald Ragsdale, University of Utah; ArtJitir Campbeli, Harvey Mudd College; and George Pimenlel, University of California at Berkeley. Special sessions are pianned for teachers of advanced placement courses and for beginning teachers. Laboratory experiments, demonstrations, computer workshops, and model building will also be included in the program. Two college credits wi!! be given for successful completion of the Institute. For further information write to: Ciaire H. Smith San Francisco University High School 3065 Jackson Street San Francisco, California 941 IS (415) 346-8400

Volume 61 Number 3 March 1984 235 Discovering Watson's Crick in High School Chemistry

Mark Whitman William Henry Harrison High School, West Lafayette, IN

The first two weeks of school present a unique blend of the these topics later, I see the lights come on when reference is good and the bad, which makes the beginning of achool a time made to our earlier discussions of "The Double Helix." of considerable adjustment for both teachers and students. I have found it necessary to conclude our study of "The Though many students possess a vibrancy and an eagerness Double Helix" with a short quiz, in order to present just re- to ieam that may well be missing by November, their attention wards to those who have pursued the book in earnest, as well spans have been adjusted over the summer to expect a com- as to those who have fallen along the way. I have real misgiv- mercial break every seven minutes. In addition, late arrivals, ings about quizzing my students over factual material from transfers, and student schedule changes serve to undercut the book, for it is not the facts which make it valuable; how- attempts by the teacher to achieve classroom continuity early ever, some students will not invest their time unless they in the school year. To accommodate these inherent idiosyn- perceive a material benefit for doing so. This is the nature of crasies best and still to achieve academic progress, I have the beast, and I am certain that the threat of the quiz en- begun each of the past three school years by assigning to my courages a number of students to read the book who otherwise first year chemistry students "The Double Helix" by James would not. Watson,3 a very readable account of the events leading to the discovery of the structure of DNA by Watson and Francis Two or three days prior to the quiz the students are given Crick. a list of main characters and a set of questions that are to be asked about the one specific character on the quiz. The During the first two weeks, I tentatively allocate half of each identity of the character remains secret, until the name is class period to discussion of "The Double Helix," but X let class pulled from a hat just before the students begin the quiz. The interest dictate. Some days the entire hour is consumed by quiz is open book, and while the students may not mark in the such discussion, while on other days ten minutes wili suffice. books, they may use blank bookmarks. The questions asked Regardless of the time spent, dividing the hour between text about the character are material and "The Double Helix" guarantees a break in discussion. Thus, the students are not forced early in the year to 3) place of employment, concentrate on one topic ibr a futt hour. In addition, allotting 2) one area of scientific expertise, substantial time to "The Double Helix," allows me to establish 3) one major scientific achievement, an academic atmosphere and to reintroduce my students to 4) one distinctive personality trait, the discipline of study, without covering so much "funda- 5) one error made which hurt his/her chances for discovering the structure of DNA, and mental" material that late arrivals will be hopelessly lost only 6) the character's reaction to Watson ant! Crick's success. two weeks into the school year. However, the true value of the book is in its content, not just in its ability to buffer the nui- In addition to an answer, the students are asked to cite the sances associated with beginning a new term. pages in the text from which their answers come. The inclusion of the citation insures that the students must become familiar Watson's narrative ss illuminating and direct, and students with the book, rather than rely upon their recall of class dis- rapidly develop a feel for the human side of science. Reading cussions; and to prepare answers for each of the main char- about Watson, Crick, Pauling, and the others who figure into acters, the students must understand the book's content. the account, students come to realize that chemical knowledge is a product of real people with real feelings and real hang-ups Each year, as I have read and reread the book and have as the book removes the shroud of mysticism that the unini- developed background material, "The Double Helix" has tiated sometimes associate with genius. One quickly comes become an increasingly important part of my curriculum. For to appreciate the role of the individual and the relations be- background information, I recommend volumes 159 and 160 tween individuals in striving for scientific achievement. of Science, which contain original reviews, as well as comments of some of the principal characters discussed in the The reading assignments coincide with start-of-the-year book. Below are some of my student objectives and some lectures intended to develop an understanding of the scientific sample discussion questions. method, and the lectures and reading complement one another well. Students find it exciting to follow Watson and After reading "The Double Helix" students should: Crick as they collect background information, develop hy- 1) know the steps of the scientific method of research and how they potheses, test the hypotheses, and formulate new hypotheses. are utilized in the book, Mapping their progress awakens the students to the fact that 2) be aware of the individual differences among scientists, and how scientific achievements are the cumulative results of the their approaches to the same problem may differ, and contributions and errors of a large number of individuals. To 3) be aware of the strong influence personalities and politics have view the blunders, as well as the achievements, is particularly on scientific achievement. enlightening. Sample questions include: I refer to the book repeatedly during the remainder of the school year. If students are to understand the flow of Watson 1) Chapters 1-3. What role do personalities and politics play in and Crick's investigations, it is necessary to discuss X-ray science? Be able to support your answer with examples from the book. diffraction, hydrogen bonding, crystallography, macromoie- 2> Chapters 4-6. What is the difference between inductive and cules, molecular geometry, and acids and bases. Obviously, deductive reasoning? Consult a dietioaary. during the first two weeks of the school year only the most 3) Chapters 22-25. What was most surprising about Pauling's superficial explanations can be made, but when we broach error? What were Walson and Crick able to determine from Franklin's work that Franklin did not know? How would you ' Watson, James B., "'The Double Helix," New American Library, characterize Watson's thinking at this point? Organized? Pro- New York. ductive? What was Watson's new hypothesis?

236 Journal of Chemical Education Edited by GEORGE WIGER California Siare University textbook forum Carson, CA 90747 Who is Anti-Markovnikov?

J. M. Tedder University of St. Andrews, Scotland, KY16 9ST

A common reaction in organic chemistry which is of wide RCHCHs HCHBrCH, commercial and academic interest is the addition of free radicals to olefins. Naturally ail organic chemistry textbooks HBt describe these reactions, and the majority discuss the factors RCHCH,Br RCH,CH2Br(+Br-) which control the rate and orientation of addition of radicals to unsymmetric olefins. Unfortunately the great majority of This occurred at the end of the 1930's, that is, at a time when textbooks give interpretations which are derived from ex- the electronic theory was having an enormous impact on or- planations of the rate and orientation of heterolytic addition ganic chemistry, and it was natural to invoke similar ideas to to similar olefins. Such analogies are extremely precarious, explain both ionic and radical mechanisms. Thus ionic addi- and they have undoubtedly led to much misunderstanding. tion was believed to yield the intermediate carbonium ion in The factors which control free radical addition reactions are which the charge was the most delocalized, so similarly radical complex, hut this cannot be used as a justification for perpe- addition was assumed to yield the initial adduct radical in trating incorrect ideas. which the unpaired spin was the most delocalized. This was long before the contribution steric compression makes to bond Chemists are usually fairly quick to accept new ideas and strengths was fully appreciated.2 At that time the relative are willing to adjust the structure of the subject to accom- weakness of a tertiary carbon-hydrogen bond was attributed modate new knowledge. Occasionally, however, new factors exclusively to resonance stabilization through hyperconju- are ignored if they appear to challenge accepted belief, in the gation in the incipient tertiary radical. However, even at that hope that further work will prove the "new facts" wrong. This time the "resonance explanation" of anti-Markovnikov ad- phenomenon occurs either when a really major breakthrough dition to vinyl chloride was unsatisfactory. is achieved which involves a substantial change in existing outlook, or when the point in question affects a fairly small 8H~-CH, :CI=CH—CH3 area of knowledge and the existing incorrect interpretations H®- give predictions which are qualitatively correct in many common cases. It is the latter type problem we are concerned C1—CH=CHS with in this article.1 Br- The question we are going to consider is: "What are the :Ct—CH—CHsBr- • ;Cl—CH—<3H,BP factors which control the rate and orientation of free radical The resonance stabilisation of the intermediate carbonium addition to aikenes?" The addition of alkyl radicals to olefins ion is reasonable; we have plenty of evidence that chlorine can is usually an exothermic reaction, irreversible at normal act as a donor when attached to a site of high electron demand. temperatures. Addition of atoms (e.g., halogens) or some In contrast, the corresponding resonance structure for the hetero-radicals (e.g., H8-, CF^S-, etc.) is often reversible. This 2-bromo-l-chSoro-ethyl radical is unimportant; it requires the article is based primarily on results involving the behavior of donation of an electron from electronegative chlorine to alkyl radicals. The arguments to be developed, however, un- neutral carbon, and it results in the formation of a dipole. The doubtedly apply to the addition of atoms and hetero-radicals contribution such a structure can make to the ground state to olefins, though experimental verification is difficult because of the 2-bromo-l-ch!oro-ethyl radical is small. Finally since of the kinetic complications associated with reversible pro- radical addition is usually a very fast exothermic reaction it cesses. would be expected to have an "early transition state," and The problem was first confronted when it was established therefore resonance stabilization of the adduct radical would that the orientation of addition of hydrogen bromide to un- be unlikely to be a major controlling factor. symmetric olefina differed according to the experimental conditions. In the presence of ultraviolet light or in the pres- The importance of other factors, expecially steric effects ence of peroxides the normal orientation of addition was re- was clearly discussed by Mayo and Walling in their seminal versed. review (2). However, the analogy with ionic addition proved too strong and emphasis on "resonance stabilization of the dark, solution phase RCHBrCH, Markovnikov adduct radical" continued to be the popular textbook explanation of the orientation of radical addition, RCH=CH5 + HBr C" More than 15 years ago it was discovered that trichloro- UV light or peroxides^ ECHICH2Br Anti-Markovnikov It was suggested almost simultaneously by Kharasch in methyl radicals preferentially attacked the unsubstituted end America and independently by Hey and Waters in Britain of vinyl fluoride because attack at the substituted end was retarded (3). Since then this has been established to be quite that this reversal of addition was due to a change in mecha- generally true and similar data is available for vinyl chloride, nism, the normal Markovnikov addition involving ions and propene, 3,3,3-trifluoropropene, acrylonitrile, methyl vinyl the anti-Markovnikov addition involving atoms and radi- ketone, etc. (.4). (At I64°C the rate of addition of trifluoro- cals. methyl radicals to the unsubstituted ends of these olefins varies by little more than a factor of two although the rate of ' The present article Is based on conclusions derived from fifteen addition to the substituted ends varies by several powers of years research aided by numerous collaborators of whose contributions ten.) Radicals attack the unsubstituted end of mono-substi- that of J. C. Walton was predominant. tuted olefins preferentially, because attack at the substituted 2 The Importance of sterlc effects in Free Radical reactions was end is retarded by the substituent. One cannot emphasize too emphasized by Ruchardt ten years ago (1).

Volume 61 Number 3 March 1984 237 strongly that orientation data by itself without kinetic data orientation of addition (cf. the orientation of methyl and tri- cannot'be used to elucidate mechanism. The fact that a methyl fkioromethyl radicals to vinyl fluoride). radical adds to the -CHg end of vinyi fluoride five times faster than it adds to the -CHP end could be because attack is en- D hanced at the -CH2 end or because it is retarded at the -CHF 17% CHsCHFCH j 164 C lCHaCHFCH3 10% end. Kinetic results show that the methyl radical adds to the However, in a polysubstituted olefin, steric effects and polarity -CH2 end of vinyl fluoride at aimost exactly the same rate it can be in opposition such that polarity has a decisive effect, adds to one end of ethylene. In other words attack occurs i.e., under these circumstances different radicals may add preferentially at the -CH2 end of vinyl fluoride because ad- preferentially to different ends of the same otefin. dition to the -CHF end is retarded at this site by the fluorine atom, i.e., the activation energy is greater for addition to the 32% 0H3CHFCF2

-CHF site. Kinetic data for a wide range of radicals shows tiiat 68% CHFCF2CH3] 164°C 5% in all the monosubatituted ethenes studied so far, attack occurs preferentially at the unsubstituted end of the molecule, We thus conclude that the rate and orientation of radical mainly because the substituent inhibits attack at the site to addition to oiefins is controlled by an interplay of steric and which it is attached. Substituents with TT orbitals of the correct polar effects, while delocalization of the unpaired electron in symmetry (e.g., CH2=CH~; -CeH^, etc.) do accelerate attack the adduct radical is only a major factor in special cases such at the unsubstituted end, but even here the very large orien- as radical addition to conjugated oiefins (e.g., styrene, buta- tation ratios are due more to lack of attack at the substituted diene, etc.). It is possible to develop some qualitative rules end than acceleration of attack at the -CHa end of the mole* (e.g., in monosubstituted ethenes addition is always preferred cule. Similarly vinyl substituents with nonbondingpaira (e.g., at the unsubstituted end), but in alkenes substituted at both ends no single criteria is adequate, and, as we have seen, dif- F-, C1-, -CH3O) have a very small resonance stabilizing effect, 3 which can be completely swamped by the resultant polarity ferent radicals may add preferentially at opposite ends. (see above). In ionic addition, cations (especially the proton) These results also illustrate another characteristic of radical add to the unsubstituted ends of propene (CH3CH---CH2) and additions. When two radicals are compared the more reactive vinyl fluoride (FCH=CH2) but to the substituted ends of radical is often the more selective. This is quite general for 1,1,1-trifluoropropene (CF3CH=CH2) and methylacylate aikyl and fluoroalkyl radicals and represents a direct contra- (MeOCOCH^CH2). In radical reactions the radical invari- diction of the Reactivity-Selectivity Principle, which implies ably adds preferentially to the unsubstituted end of these a decrease in selectivity with increasing reactivity. The reason oiefins and kinetic studies confirm that this is attributable to for this breakdown of the Reactivity-Selectivity Principle greater activation energies for addition to the substituted when CH3 and CFg are compared is that the more reactive site. radical (e.g., CFa') is also that which leads to the more polar transition state (7). Experiment shows that steric effects are of major impor- Radical addition is a very important process by which many tance in determining the orientation of radical addition. Al- polymers are prepared. Mistakenly, it is usually introduced though most radical additions are exothermic the approach in textbooks as an exception (i.e., anti-Markovnikov addition of the, radical to an olefih carbon atom in the transition state of HBr), and th$ explanation usually given is aimost always is sufficiently close for the increasing steric compression (i.e., misleading and sometimes wrong. Unfortunately, the true mutual repulsion between the nuclei, their bonding electrons, picture is more complicated than the various single alterna- and adjacent atoms) to be important. It will be expected that tives, but nature does not organize herself for our benefit. bulky radicals are particularly discriminating. Thus, at £64°C trichloromethyl radicals add at approximately the same rate Literature Cited to the -CFa end of CF3=CHF and CF2-=CHC1, but attack the (j) Riiehardt, C, Angm. Ckem. Ira. Ed. EngL, 9,831) (1970). -CHF end of the former olefin approximately 85 times faster (2) Mayo, F. C, arid Walling, C, Ckem. fiees.,«. 266 (1950). than the -CHC1 end of the latter olefin.3 (3) Tedder, J. M, nod Walton, J. C, Prix. Chum. Sac., 420 (1964). U) The kinetk' date referred to in this article has been collected tn three compilations: (a) J4PFT, J. A., and Parsonage, M. J., "Evaluated Kinetic Data en Cai Phase Addition Reactions," Butterwortha 1973; (b) Kerr, J. A., and Ralajraab, E., "Kccnnd Supple- OIsCFjCHI? +CF3CHFCCI mentary Tables of Bimolecular GBS Reactions," University of Birmingham, 1973; k) x = Kerr, J. Ar, and lla]ajC£ak, E,, "Third Supplementary Tabtee of Rimolerular Gas 22% 78% Reactions," University «f Birmingham. 1977. (5) The inclusions have been summariwd in (al Tedder, i. M, and Walton. J. C, Accounts +c Cham, ffes., 9,183 (197«>, (W Tedder, j. M.. and Walton, J. C, ACS. Symposium 1. 3 \<164°C) Scries, B6,107 (1978). CHX \ (6) (a) Tedder, J. M., and Walton, J. C, Tetrahedron, 8fi. 701 (1980); (b) Tedder, ,1. M.. x = Angetu. Chum. Internal. Ed. (EngL), 21,401 (1982). CCUCFXHC1 + CFiCHClCCU (71 Giese. B., Angeic. Chem. Int. Ed. Ens'-, 16,125 (1977).

Fluorine and chlorine have similar electronic properties (i.e., Table 1. Orientation and Relative Rate of the Addition of both are electron-attracting donors), but their size is very different. The importance of the size of the radical is well il- Perfluoroalkyl Radicals to Vinyl Fluoride CH2-==CHF lustrated by the orientation of addition of perfluoroalkyl (160° C gas phase) (from ref. (3)) radicals to vinyl fluoride (cf. Table 1). Notice that although fladical* CF CFsCFj- (CF ),CF. (CF313C- the orientation ratio a:{5 varies 200-fold, the relative rate of r 3 addition to the a site and to ethylene varies by less than a a:fi 1:0.1 1:0.06 1:0.02 1:0.005 factor of two. 2ko/ke 0.5 0.6 0.5 0.5

Although Steric factors are predominant, polarity does in- ' k = role COEstanla for addition To ethyiene fluence the rate of reaction (cf. Table 2). Table 2 clearly shows B that fluorine atoms in the olefin enhance the rate of addition of methyl radicals, which therefore behave like "nucleophiles," while the same fluorine atoms retard the addition of trifluo- Table 2. The Ratios of Addition to Tetraftuoroethylene and romethy! radicals, which behave like "eiectrophiles." Ethylene by Methyl and the Fiuoromethyl Radicals, (164°C gas Steric effects normally overrule polarity in determining the phase) (from ref. (3))

Radical CH3- FCHa- F2CH- 3 Rules for determining Bis rate and preferred orientation ol radical 3.4 1.1 0.1 addition have been given in ref, (6a) and in greater detail in ref.{6b). 9.5

238 Journal of Chemical Education edited by: DAVID A. PHILLIPS Wabash College Crawfordsvllle. IN 47933 PRUDENCE PHILLIPS Crawfordsviile High School Goal/ Crawfordsviile, IN 47933

Why Teach Organic Chemistry The Place of Organic Chemistry in the High Medical schools suggest that calculus and organic chemistry School Curriculum distinguish students who have analytical abilities from those At Detroit Country Day School, approximately one-third who have cluttered minds. Analytical ability is one quality the of the course time in second-year chemistry is spent on the medical schools look for in prospective candidates. After study of organic chemistry. This is rather unusual because teaching organic chemistry at several levels for 42 yeara I most high school courses tend to concentrate on the physical would not quarrel with this view. However, I do doubt whether or descriptive side of inorganic chemistry. If organic chemistry learning to think analytically in one field transfers to another is mentioned at all, it is usually in a brief survey of simple situation, For example, I can think of more than one famous functional groups with a mention of combustion, addition, and chemist whose views on political questions were completely esterification reactions. This amounts to a memory exercise prejudiced and unreasoned. In the history of chemistry there and provides the student with no depth of understanding of are examples of scientists who clung to theories long after the molecular interactions so vital to the nature of chemistry. evidence was overwhelming against them. These problems are noted in a recent paper dealing with trie This does not discourage me, however, as I look elsewhere inclusion of organic chemistry in the CHEM Study program.1 for reasons to learn some organic chemistry. Today a citizen The many reasons for our focus on organic chemistry are cannot read a newspaper intelligently without some knowl- elaborated upon in the following paragraphs. edge of organic chemistry. Certainly advertisements for as- Students enjoy organic partly because it is a break from the pirin can be read more critically if one knows that aspirin is constant emphasis on the quantitative nature of chemistry. a single pure substance. How then, can one brand of aspirin There is an underlying beauty in organic reactions stemming be better than another? Of course one company may have from the predictability afforded by our detailed under- better safety precautions for testing than another, but that standing of reaction mechanisms. This provides an exciting is a matter of trust.in proceedings, not a property of a sub- challenge to students and truly tests their understanding of stance, and generally not the point of the advertisement the material. Because natural and man-made products of In the last few years I have taught principally pre-medical organic reactions are so common and important in all aspects students. I have had conversations with former students now of life, students take a different view of chemistry and practicing medicine who are proud to tell me that they have chemists. They come to see that chemists are not people who not used organic chemistry since they left my class. I know merely solve problems on their calculators but that they also that this cannot be true, because what I have tried to leave are involved with exciting synthetic procedures and inter- with them after they have forgotten the mechanism of the esting laboratory experiences. Cannizzaro reaction, the utility of a Grignard reagent, and the Our first-year course is a comprehensive one which covers structure of glucose include the following. most of the traditional topics: atomic structure, bonding, 1) Some feeling for the limitations of the measurements gases, solution chemistry, thermodynamics, kinetics, equi- they get from laboratory technicians. In particular, doctors libria (including acid/base chemistry and solubility), oxida- need to be aware of the limitations of instruments, as, for ex- tion-reduction reactions, and electrochemistry. Beginning in ample, in determining the amount of sugar in a urine the fall of the second year, organic chemistry is introduced. sample. One very important reason for this is to review, in a new con- B 13 lfl text, many of the major concepts taught previously. Students 2) The use of tracers (D, T, * 0, C, N, and others) in need a thorough review of the introductory course (especially following the pathway of a chemical reaction. Such tracers if a year has elapsed since their first exposure) in order to place may be used in medicine to follow the pathway of a drug in the these topics in the proper perspective. Rather than repeating body. the same examples, reinforcement of important principles 3) Some appreciation that proteins, carbohydrates, and fats comes from using organic chemistry. as well as amygdalm (laetrile), ascorbic acid, dioxin, nylon, and cocaine are chemicals. The course begins with a discussion of bonding and hy- 4) Some notion of the problems they may encounter in bridization, using carbon compounds as examples, Emphasis practicing medicine. A doctor I met in India who had practiced is placed on the stereochemistry of these compounds, and both II years in this country before returning to his native land structural and stereoisomerism are introduced. Nomenclature said, "The. most trying problem I face day-to-day is telling a and the reactions of various functional groups are then dis- patient that he could cure his illness by eating better food cussed. Oxidation of alcohols provides a review of balancing when 1 know he can't afford it." What should he say to his patients? Where better to think about ethical problems than 1 Beasley, W., CHEM. EDUC., 57, 807 (1980).

About theAuthors LeaByrt B. Clapp is Emeritus Newport Rogers Professor of Chemistry Mary C. Johnson has taught chemistry lor thirteen years in the Detroit at Brown University In Providence, Rhode island. He has had a distin- area. For the past three years she has been a chemistry teacher at De- guished career in chemical education, serving as chairman o! the Divi- troit Country Day School Irs Birmingham, Michigan, where she is currently sion, as a participant In (he visiting Scientist Program, and as a member Involved In leaching regular and honors first-year chemistry and honors of numarous committees concerned wilh the teaching of chemistry and second-year chemistry. Last year 106 students wore enrolled in her the preparation of high school teachers. Among tha numerous honors classes. She received her B.A. degree from Western Michigan University accorded him are the MCA Award in College Teaching and foe Division's in Kalamazoo, Michigan and her MS degree from Wayne Stale University SAMA award. HB received his B.Ed, degree from Eastern illinois State in Detroit, Michigan. College and his MA and PhD degreeee from the University of Illinois.

Volume 61 Number 3 March 1984 239 in the organic class? In 1946, DDT was used to spray for oxidation-reduction reactions as well as an introduction to mosquitoes in Sri Lanka, and the death rate from malaria aldehydes, ketones, and acids. The study of carboxylic acids diminished from 30 to 22 per thousand population in one year. affords an opportunity to reemphasize the importance of Some years later some of the people of Sri Lanka starved to equilibrium, particularly with respect to weak acid/base death because there was not enough rice for the extra people chemistry, and the relationship of pKa, equivalence point, who had escaped the ravages of the disease. Was it ethical to buffers and indicators to the titration procedure. Mechanisms supply DDT in the first place? play a vital role in modern organic chemistry, and discussions 5) Organic chemistry is part of our culture. Culture is what of SN1> SN2, El, and E2 reactions follow directly from a review remains when you have forgotten all that you learned. Organic of kinetics and the orders of reactions. Polymers and medicinal chemists have added to our cultural heritage in a very short chemistry are other topics which can lead into discussion of time. Even today's 20-year-olds have iived through about many relevant issues facing today's society, and these subjects one-seventh of the entire history of organic chemistry. In 1828 would be difficult to study without a knowledge of molecular Wohler synthesized urea (an animal substance) from ammo- structure. nium cyanate {strictly a mineral substance) and forever re- Organic reactions can be used to introduce many new lab- moved the mystery which previously had held the synthesis oratory techniques. Kinetics experiments such as the oxida- of an organic substance required a "vital force." Citizens, tion of ethanol {followed titrimetrically)3 and the broraination chemistry majors, and pre-medieal students ought to appre- of acetone (followed spectroscopically) are two examples. Of ciate some of the clever thinking and strenuous laboratory course these experiments could be performed without any work that have highlighted accomplishments in this field in knowledge of organic chemistry. However, students have a the past—Emil Fischer's proof of structure of glucose and his better appreciation of the experiment when they understand synthesis of a peptide of 18 units; du Vigneaud's and Tuppy's the reaction behind the procedure. Each student is required work that resulted in elucidating the structure of the first to synthesize and purify a different organic compound and proteins, the pituitary hormones oxytocin and vasopressin; then, using instrumentation available at a nearby university, Carothers' work on polymers; and Woodward's remarkable to verify its structure by NMR and IE spectroscopy. Students synthesis of chlorophyll and many other complex mole- enjoy the challenge of searching the literature to find a suitable cules. procedure and then making the proper analysis. As in all young sciences, theories and research in organic On the more practical side, students have found that a chemistry are still empirical in many respects, although background in organic chemistry is an advantage when they quantitative explanations are slowly creeping into the field. go on to their college studies. Some take survey courses in their The role of catalysts, particularly heterogeneous catalysts, is freshman year which include organic and biochemistry. The still a dark corner to be explored. pace of such courses is usually rapid; prior exposure to the Students say that chemistry is less "cut and dried" than subject is of great value. Other students place out of first-year physics, by which they imply that every phenomenon in chemistry and go directly into organic, a very challenging physics has already been explained. Instead, what they mean course at the university level. Students with some organic is that in chemistry it is easier to get to the edge of research background are less bewildered by the introduction of many than it is in physics. In biology it is still easier for a beginner concepts in quick succession. Also, students from our course to make a contribution, because many biological problems are already familiar with reftuxing, distillation, recrystalli- yield to empirical methods, At the moment chemistry is in the zation, and some chromatography techniques and feel much ideal position between these two disciplines. more at ease in a college lab. Finally, our school follows the curriculum of the Interna- Leatlyn B. Clapp tiona! Baccalaureate, a program involving a rigorous course Brown University of study over a broad range of disciplines, and organic is a vital Providence, Rl 02912 aspect of the chemistry covered in this program. However, even if our school were not involved, I still would try to place a major emphasis on the teaching of organic chemistry in either a second-year or a third-semester of high school chem- The 1984 International Chemistry Olympiad istry. Since a great deal of all chemistry done in industry, in- In Frankfurt/Main (West Germany) cluding agricultural, pharmaceutical, paint and polymer The 16th International Chemistry Olympiad will be held in chemistry, involves organic reactions, it does seem strange to Frankfurt/Main (West Germany) from June 30 to July 10, leave such an enormous wealth of material out of the curric> 1984, with more than 20 countries participating. The four best ulum, even at the high school level. pupils from each country are given the opportunity to test their skills against these of others. Participants must perform both In previous years, I have taught a one-semester course of theoretical tasks {from all spheres of chemistry) and practical organic chemistry to non-honors students, using common high laboratory work, these assignments going far beyond what is school equipment along with old glassware donated by a required in school. university. I have found that we could make a decent attempt An extensive information and cultural program provide? a at good lab experiments without a tremendous outlay of funds. chance to become better acquainted with the host country and The course does not have to be a rigorous one, duplicating a its people. Many students find that the Olympiad allows them college-level course, to be interesting and educational to the to transcend political and ideological boundaries and to es- student. My only regret is that at present I do not have enough tablish contacts and make friends; this may well be the most time in the first-year course to offer more than a superficial valuable contribution of the International Olympiad. sketch of organic chemistry for those who will not be going on The Olympiad {as well as some of the requirements for to the second-year class. participation) has been described in: Ellis, P. R., Educ. Chem. 20,208 (1983). Mary C. Johnson For further information concerning participation ra the 1884 Detroit Country Day School International Chemistry Olympiad in Frankfurt/Main con- Birmingham. Ml 48010 tact: StD Klaus Hagenstein Geschaftsfuhrer der 16. Internationalen Chemieoiyropiade Brandsbornstrasse 11-15 D-6050 Offenbach, West Germany Finlayson, M. E., and Lee, D. G., J. CHEM. EDUC., 48, 47 (1971).

240 Journal of Chemical Education edited by ROGER B. FESTA Northeast Missouri State University profile/ in chemi/try Kirksvllie, Mo. 63S01

Neoprene and Nylon Stockings The Legacy of In 1920, Carothers left Tarkio College with a bachelor of Wallace Hume Carothers science degree. He began his graduate studies in the chemistry department of the University of Illinois. After one year, he had Carol Cummlngs completed the requirements for the master of arts degree but Warren Township High School lacked funds for further study, Carother's former instructor Gumee, iL 60031 at Tarkio, now chairman of the chemistry department at the University of South Dakota, was looking for a young instructor What do rubber tires and nylon stockings have in common? to teach analytical and physical chemistry. Carothers was They are both made with synthetic substances developed by chosen for the position and went to South Dakota with the the brilliant chemist Wallace Carothers. Neoprene was the idea that he would make enough money to complete his first successful synthetic rubber developed in the United graduate work. The careful preparation of his courses and his States. It has a wide variety of uses from tires and life rafts to concern for the students demonstrated that he could be a very sealants for space vehicles. Nylon revolutionized the textile successful chemistry teacher. industry by ushering in the era of synthetic fibers. In addition to its use as a textile, nylon has many applications as a molded Carothers started to develop some independent research plastic. Today, many well-dressed women would not consider project* while he was teaching. His first contribution to the leaving their homes without wearing nylon hose. If Carothers Journal of the American Chemical Society was "The Iso- only knew what he had started! sterism of Phenyl Isocyanate and Diazobenzene Imide" in 1923. His second paper, in 1924, was "The Double Bond," in Wallace Hume Carothers was born in Burlington, Iowa, on which he presented the first dear application of the electronic April 27,1896. His paternal forebears were farmers and arti- theory to organic chemistry. It became evident that teaching sans of Scotch origin. His father, Ira, was born on a farm in was not his primary interest, and he spent all of his spare time Illinois but left the farm at age 19 and taught country school. on research projects. His friends urged him to relax, but it was Later, he entered the field of commercial education and was as if he were driven by an inner desire to investigate. a teacher and eventually vice president of Capital City Com- mercial College in Des Moines. His maternal ancestors were Carothers returned to the University of Illinois in 1922 to farmers of Scotch-Irish stock who loved music, It may have complete his studies, and in 1924 he received the PhD in or- been the influence of his mother, Mary Evalina McMullin, ganic chemistry. His thesis research explored the catalytic that led to Carothers' keen interest in and appreciation of reduction of aldehydes with platinum-oxide platinum-black, music as an adult. and the effect of promoters and poisons on this catalyst in the reduction of various organic compounds. These studies were Carothers was the oldest of four children, He was especially completed under the direction of Roger Adams, the legendary devoted to his sister, Isobel, who achieved radio fame in the Illinois chemist who trained his research students as careful early 1930*s as Lu in the trio Clara, Lu, and Em. When she experimentalists and inspired in them an intense interest in (tied suddenly in 1936 after a short illness, Carothers was chemistry. Adams was strongly oriented toward the chemical greatly shocked, and he never completely adjusted to her industry, and this attitude apparently influenced Carothers. loss. While at the university, Carothers also studied physical When Carolhers was five, his parents moved to Des Moines chemistry and mathematics. He held assistantships in inor- where he began his education in the public schools. He grad- ganic and organic chemistry, was promoted to a research as- uated from North High in 1914. During these years, he dis- sistant, and was later granted the Carr Fellowship, the highest played an overwhelming interest in tools and mechanical award offered by the chemistry department. things and spent hours experimenting. Carothers was a per- fectionist. He carefully finished every task he started. After graduation, Carothers was appointed instructor in Carothers enrolled in the Capital City Commercial College organic chemistry at the University of Illinois where he taught in the fal! of 1914 and graduated in the accountant curriculum for two years. In 1926, he was chosen to fill an organic chem- in July 1915, In the fall he entered Tarkio College in Missouri, istry position at Harvard University. During his first year at where he pursued a scientific course and also accepted a po- Harvard he taught experimental organic chemistry and an sition as assistant in the commercial department. Carothers advanced course in structural chemistry. It was here that excelled in his chemistry courses and, after two years, his su- Carothers began his studies on polymerization. Then in 1928, perior record in English earned him a teaching assistantship Du Pont began a new program of fundamental research at the in that department. Then, during World War I, Arthur Par- Experimental Station at Wilmington, Delaware. Carothers dee, head of the chemistry department, accepted a position was asked to head the organic chemistry program, and it was at another institution. Carothers, who had taken all of the at this time that he permanently left education. chemistry courses at Tarkio by the end of his sophomore year, Prom the time Carothers joined Du Pont until his death, was appointed to take over the chemistry instruction. He had his accomplishments were plentiful and of great value. During been rejected as a soldier because of a goiter condition, so he the nine-year period that he was with Du Pont, Carothers not served as a chemistry teacher during his junior and senior only made numerous contributions to the theory of organic years while he completed his studies. chemistry but also provided inspiration and guidance to the chemists under his direction. His work laid the foundation for several new developments of commercial importance. "Profiles In Chemistry" is a biographical feature, highlighting the The first area which he studied extensively was acetylene contributions ol distinguished chemists in the contexi of their Hves. The polymers and their derivatives. Julius A. Nieuwland, a priest column ts designed for curriculum enrichment, ailowing the secondary schooi teacher to enhance the vitality oi chemistry with the sense of at the University of Notre Dame, had completed the basic scholarship and adventure shared by chemists throughout history. research on the synthesis of vinylacetylene and divinylacetylene. When a chemist from Du Pont heard Nieuwland's

Volume 61 Number 3 March 1984 241 presentation at an American Chemical Society Organic spoke before the Faraday Society in London on "Polymers and Chemistry Symposium in 1925, he realized that Nieuwland's the Theory of Polymerization." He was the first industrial knowledge could be valuable to Du Pont, and an association organic chemist to be elected to the National Academy of was formed. Now that vinylacetylene and divinylacetylene Sciences. Apparently Carothers never regretted his decision were available to Carothers, he completed a detailed study of of research over teaching; he turned down several academic these substances. Further, he found a way to add hydrogen positions during his years at Du Pont. chloride to mono vinylacetylene to form chloroprene. This On February 21, 1936, Crothers married Helen Everett substance is structurally analogous to isoprene, but polym- Sweetman of Wilmington, Delaware. She had received her erizes several hundreds of times faster to produce polychlo- bachelor's degree in chemistry at the University of Delaware roprene. The first polychloroprene was named duprene; and was employed in Du Pont's chemical patent division. however, Carothers changed the name to neoprene. Neoprene Carothers was an avid reader and especially enjoyed poetry. resembles rubber and is used as an additive to natural rubber He also liked to sing, and he found it very relaxing to listen to to improve its properties. The first large-scale application of his many recordings of great composers such as Bach, Bee- neoprene was for the production of gasoline hose which could thoven, and Brahms. Carothers was shy and sensitive, and he withstand attack by gasoline and hydrocarbons. Today, Du avoided parties and crowds. His close friends described him Pont produces about 175,000 tons of neoprene a year, which as deeply emotional, generous, and modest. In very small results in sales of about $400 million annually. groups, he was a brilliant conversationalist. While investigating the chemistry of polymerization, Car- Carothers suffered from a nervous condition, revealed in others also synthesized some cyclic polymers which possessed his later years, in his poor health. He was plagued by periods a musklike aroma. Du Pont marketed these substances under of depression which became more and more pronounced. On the trade name Astrotone synthetic musk for the perfume April 29,1937, at the age of 41, he checked into a Philadelphia industry. hotel and committed suicide by drinking cyanide. He never Carothers' most outstanding scientific accomplishment was saw his daughter, Jane, who was born seven months later. his work on linear polymers. He wrote a series of 31 papers in Despite the brevity of his career, Carothers' contributions to the field of polymerisation and held 50 patents. In these pa- organic chemistry are recognized as outstanding, and he is pers, he proposed a theory of condensation-polymerization acknowledged as a pioneer in the field. and a terminology suitable for this field. During the 1930's Carothers devoted his attention to the preparation of polymers which were structurally analogous to cellulose and siJk. References Many compounds were studied; however, the results were Adams. Roger, "National Academy of Sciences of tfie USA, Biographical Memoirs," disappointing. Du Pont was on the verge of abandoning the Washington. 1939, p. 21). project when in 1935, success was attained when nylon was Father, Ed (Editor], "Great Chemiata," Interecienee, Now York, IWSI. Findisy, Alexander, "A Hundred Vears of Chemistry," Humanities, NJ.I96B. developed. Nylon is a macromolecule obtained as a conden- Haasler, WiJliam W.,"HowNytati Was Discovered," Amerkan History, 5, Z2(197Gj. sation product from adipic add and hexamethylene-diamine, Ihde, Aaron, "The Development of Modern Chemistry," Harper and Row, Now York. with a molecular weight of over 10,000. Nylon has become a £964. Lochemann, Georg, "The Story of Chemistry," PhiloaophtcaJ Library, Philadelphia, fiber particularly suited for textiles. 19S9. Mifos, Wyndhara IX {Editor)* "American Chemists and Chemical Engineers," Amflrican Carothers' advice was sought hy chemists throughout the Chemical Society. Washington, 1B7*. world. At the age of 33, he was elected associate editor of the "Neoprene Celebrates e HaJf-Century of Commercial Success" Chemical and Engineering Journal of the American Chemical Society. The following Tarbcll, D. S., Tarlwll, A. T., and Joyce, R. M., Isis, 71, year, he became the editor of Organic Syntheses. In 1935, he "The Father of Neoprene," Notre Dams Neant, 10,4 (1981).

The Density of Solids

Dale Burgess Eastern Wyoming College, 3200 West C Street, Torrington, WY 82240

An experiment to determine the density of a solid usually do not fit easily into a graduated cylinder or are too heavy to is a simple one in which the student carefully slides a cylinder be weighed on the triple beam balances, so the students must of metai into a graduated cylinder partially filled with water think up ways to weigh the objects using the trip balance and in order to determine volume by displacement and weighs the to determine the volume with a reasonable degree of accu- metal cylinder. The student calculates the density from the racy. formula D = M/V and answers a few pertinent questions. There is generally a short period of student confusion and In my experiment, however, I have a large collection of as- aimlessness, but then the students start getting ideas and the sorted objects. This collection includes rebar, concrete, boards, experiment becomes both challenging and fun for most of rocks, gears, hose, pipes, corks, styrofoara, rubber stoppers, them. In my last class a couple of the students found a box that and odd pieces of metal. contained vermiculite that had been used as packing, and they Each student is given one of the objects and is told that he used the vermiculite as a displacement medium and the box can use anything in the lab in his determination of the object's as a container to determine the volume of a large board. density, but that the size of the measuring device must have Following the experiment I discuss: (1) the comparison of an accuracy commensurate with the size of the object being the measured densities with the real densities, (2) the com- measured. The volume of the object must be obtained both parison of the results of the two methods, (3) the possible er- by displacement and by using a ruler to get its dimensions. rors introduced by the measuring devices, (4) relative error The students have the normal chemistry lab equipment and in the experimental data, and (5) other methods of density some large pans to be used for large object displacement. determination. The discussion of relative error leads nicely There is also a trip balance with no weights. The objects either into a discussion of significant figures.

242 Journal of Chemical Education Use of the Computer for Chemistry Instruction

Robert Sutler Portage Northern High School, 1000 Idaho, Portage, M! 49081

In these times of rising costs and decreasing revenues, one NAKE iiBSEHCES POINTS GRADE must be able to work as efficiently as possible. At the achooi system where I teach chemistry we have seen a drastic decrease in funds, resulting in many changes. Therefore, the ADAMS J 0 243 A- teacher must be able to work smarter, rather than harder. BGE 1 0 217 8- Several years ago, I purchased an Apple II computer with GARV R 2 25S A an Epson MX-80 printer. Since I had programming experi- 30NES H 1 1% C ence, adapting to the Apple presented little difficulty for me. The personal computer has been the greatest invention for the KILLER R 0 225 teacher since the chalkboard. It has allowed me actually to PHILLIPS F 2 203 increase my efficiency without compromising quality. How- SRIIH J 3 24!) B+ ever, one must be careful to do only tasks with the computer that actually result in time saving. Too often, the computer TAYLOR S i 198 C ts used to accomplish tasks that can be done better without WHITE B 0 2U C+ it. SUMRftSY Gradebook TftBLE In our school system, student grade reports are issued six times per school year. As any teacher is aware, considerable time is needed to determine grades and, because of the sheer h- 2 number of grades being calculated, errors will inevitably re- B-- 3 sult. Therefore, I decided to use the computer as the gradebook. This allowed me to compute the grades for all my stu- C- 4 dents in a matter of minutes. At the end of each week, I spend D~ 0 about fifteen minutes entering scores into the computer. 0 When the grades are due, I simply enter the grade cut-off E-- point and the computer determines the grades. Then I have the grades transferred from the printout sheets to the school's POSSIBLE POIMTS - 263 report card sheets by my student assistant. My actual time FAILING 60 1 involved in preparing grades is a few minutes, rather than mm — hours. Since I have extensive programming experience, I decided to write my own gradebook program, rather than buy a 6RADIN8 SCALE packaged one. In this way, I could design the program to fit my needs exactly. Admittedly, it was a considerable amount ft+ 255 - 263 of work, but well worth it. My gradebook program will perform the following: A 24S - 254 A- 241 - 247 record scores record absences 8* 232 - 240 determine test score averages 6 222 - 231 determine total points for each student B- 212 - 221 determine letter grade for each student determine the number of each grade given per class Ct 201 -.211 allow for addition or deletion of students C 190 - 200 permit either screen or printer display (see Fig. 1> allow for easy changing of information C- 178 - 189 fi* 171 - 177 The records in the program are stored sequentially on the disk. An added advantage of the program is that a student is able D 164 - 170 to determine his or her grade at any time during the marking D- 15? - 163 period. Therefore, he or she knows how hard to work in order to improve the grade. Naturally, the program must have a security system that will permit the student to check only his FAILING SCORE - 60 7. or her grade, not change it. I use a password system that prevents the unauthorized modifying of grade records. The Figure 1. Sample printout of computer gradebook. password uses control characters which cannot be seen by listing the program. ords data, and has no idea if the experimental results are correct or not. The student generally does not learn whether Chemistry Laboratory the experiment has been done correctly until the graded ex- The microcomputer is also very useful in the laboratory. periment write-up is returned. Therefore, I have written a Too often, the student simply performs the experiment, rec- number of programs that will permit the student to check his

Volume 61 Number 3 March 1984 243 or her experimental data right in the laboratory. The student using the telephone Sine, which enables one to contact chem- performs the experiment, enters the data into the computer, ical information services such as CAS ONLINE. A very and then the computer informs him or her whether the data valuable exercise is to have the student perform a compound is good. If it is not, the student knows to repeat the experi- search using this facility. ment. Since I began using the computer in the laboratory, the work of my students has improved considerably. Communicating with the Student I have also attempted to have the student first type his or When writing programs for student use, one must realize her name before entering any data. The idea was to record the that very few of them have any computer experience. The student's name and data, use the computer to calculate the simple instruction "ENTER NAME" will confuse many of experimental results, arid save all this information on the disk. them. It would be better to use "TYPE NAME, THEN When checking lab reports I would be able to recall the in- PRESS RETURN." Also, the numbers one and zero are formation from the disk, and then compare their calculations confused with the letters 1 and o. Numerous error-trapping with the computer's. This should make lab report grading very routines are required. After the students enter their data, one easy. However, it has not worked out that way. The, problem must make provisions for the correction of errors. I use the is that there is only one computer available and lab periods statement: are only one hour long. Most students have no typing skills or computer experience. A non-typist may require several min- CHECK YOUR DATA. 18 IT CORRECT

1 Dletz, P., Tellefsen, R., Parry, Ft., and Stefner, L, "Chemistry Ex- perimental Foundations: Laboratory Manual," Prentice-Hai!, Englewood Cliffs, New Jersey, 1975. --17 aJohn Bell Engineering, Inc., 1014 Center Street, San Carlos, CA 94070. 3 Deininger, R., and Berger, C, InCtder, 74 (January 1983). Figure 3. Titration simulation.

244 Journal of Chemical Education his turn at the computer, and the following instructions appear test and make numerical and nomenclatural changes. Thus, on the screen: the main body of the test remains the same; this is especially useful for preparing makeup exams. (1) PRESS (RETURN) FOR ANOTHER SET OP DATA There are several features to look for in a word processor. (2) PRESS (E> TO EXIT PROGRAM First, there must be provision for subscripts and superscripts. Option (1) should be selected so that another person can use Without this ability, it is difficult to write formulas or expo- the computer. However, since most students have no idea of nents; however, it may be inconvenient to use these features what exit means, they will select this option when done. The because special printer codes are required. My word processor instructor will have to reload or rerun the program, On the uses the ESC key for upper case, and control keys for sub- other hand, there are the hot-shot programmers who like to scripting and superscripting. Writing the formula for sulfuric get a listing of the program and then change the commands. acid uses the following key sequence: Therefore, if possible, disable the reset key.4 ESC H CTL B ESC 4 OTL B ESC ESC S CTL B12 CTL Database System B ESC 5 ESC S ESC 0 CTL B ESC 4 CTL B ESC ESC H CTL B 1 4 CTL B ESC 5 A database program is similar to a computerized index card system. It will store information for easy retrieval. There are It is hardly worth the trouble. many database programs available. Examine several before Second, the screen display should indicate exactly how the making a decision. document will appear on the printed page. One must know One use for the database program is stockroom inventory. where the margins and the end of the page will be. When I Since we have a large chemical stockroom, computerization write a question on a test, I leave space for the calculation and seemed the logical choice. One can have information con- answer. Therefore, I must know exactly how it is formatted cerning the name of compound, class, amount, etc. One of the and where it will be on the page. features of database systems is their ability to sort and search. Next, it is very helpful if one can see an entire line of text. If one wants to know what bases are available in the stock- Since my computer has only a 40 column display, and the room, the computer can be instructed to search the base printer 80 columns, this could be a disadvantage. There is classification and al! these compounds will be referenced. hardware available that will give an 80 column display but this Another advantage of the computerized stockroom is that one is often expensive. My solution has been to purchase a word has instant access to the chemicals that are available. Since processor which uses the computer's hi-res graphics to show I do not have an office in school (it was converted into a 70 columns and lower case. I have been using the Magic classroom), al! my reference books are at home. If I find a Window II word processor by Artsci and have been extremely promising experiment that I would like to try, I can easily pleased. My only complaint is that it is protected software; it check my computer listing to see if the required chemicals are is not possible to make a back-up copy of it. The company does available. offer a liberal warranty, but if for some reason I accidentally damage the disk, I will not be able to access any of my docu- Another use of the database program is to record student ments until a replacement disk arrives, data, such as home phone number and hook number. If a student leaves his book in class, I simply have the computer To print numerous copies of any one document it is neces- do a search to find the owner. Also, one can keep a permanent sary to make dittos because we do not have access to a pho- grade record of the students. One problem with the database tocopier. There is a problem, however. A dot matrix printer program is that a considerable amount of time is needed to does not impact hard enough to make a ditto. Thermofax® record all the information. It is very helpful if one has a stu- dittos of the original can be made, but this does not always dent assistant who is able to type. produce a clear copy. Therefore, to get around this problem I make a ditto using a Thermofax® master directly in the When selecting a database program, be certain that it uses printer. In order to obtain best results I use both the double machine language for sorts and searches. The first program strike and emphasized printing modes. In addition, I remove I tried did not, and an hour was required to sort 175 chemicals. the printer ribbon so that the pins strike directly on the My present database program can accomplish this task in a Thermofax master. few seconds using machine language. One final problem is that my printer is tractor feed only, and Word Processing Thermofax® dittos will not pass through. One solution is to tape the ditto to the paper. A better solution is the purchase The term "word processing" is computerese for typing. The 5 word processor is probably the most used progam that I have. of a Paper Porter. This is a plastic sleeve carrier that will With it I can write letters, tests, and experiments and edit allow regular paper or dittos to go through the printer. them as needed. Once satisfied with the document, I can have it printed out. The document can also be saved on disk if I VISICALC® desire. The VISICALC® program is an electronic spread sheet. It Since I am not able to purchase textbooks for my organic can be used to make forecasts or projections as well as store chemistry ciasa, I must generate most of the written materials data. We have used the program to perform calculations with used. The word processing capability of my computer has large amounts of data. A number of teachers use this program proved to be a valuable resource, especially when I am pre- for their gradebooks. Recently, we have used Visicale® for paring lab experiments. Once I type them, they are saved on contract negotiations. The current salary schedules were disk and updated as needed each year. placed in the program; then, using the projection feature of the program, our school system could see how the values would I iike to give my students as many practice problems as change if certain percent pay increases were granted. The possible, and it seems they are always asking for more. To administration may want to use Visicalc* to make projections handle this demand, I prepare a master worksheet using the of student counts, costs of utilities, etc. Visicalc® is probably word processor, and need only to add new data to produce any one of the most important programs ever written for the subsequent worksheets. For example, if I am writing a mo- computer. larity practice sheet, I typically vary only the names and amounts of the given substances. I have described a few ways in which the microcomputer can The same technique can be used to write tests. I had found be helpful to the classroom teacher. I would never want to be even before I began using the word processor that my tests without one again. follow a similar pattern year after year. Thus, with the word processor, I have freed a considerable amount of time that can 4 Sottalk, 44 (March 1983). be used more productively elsewhere. I typically take an old s Beeline Services, 5718 Ponderosa, Stevensvlile, Ml 49127. Volume 61 Number 3 March 1984 245 The Basic Elements of Writing a Scientific Paper; The Art of Scientific Style

Carol Potera1 Eleanor Roosevelt Institute for Cancer Research, 4200 East Ninth Ave., B-129, Denver, CO 80262

Winston Churchill is reported to have said of literary critics above all in particular who insisted that sentences never end in a preposition (i), accordingly instead "This is the type of arrant pedantry up with which I shall not and so in summary put." This historic example of what is and what is not con- again likewise sidered proper in good writing applies to technical scientific also moreover writing as well as other, more literary forms of communication. besides more specificaify For those who do not write regularly, the experience can' he but nevertheless intimidating. Knowing what is important and reviewing some consequently nonetheless common pitfalls of science writing at the outset is always finally on the otJwr hand helpful. first rather for example second Scientific writing is a form of writing called expository. Its for instance similarly primary goal is to explain. Implicit in any expository writing furthermore so is another goal: to persuade. The two go hand in hand, for it hence still is hard to explain a scientific fact without taking a position on however tiien it The goal, then, is both to have your readers understand you in addition therefore and to convince them that your interpretation of your data in conclusion though is the only correct one. indeed thus in fact to sum up yet Correct and Concise Usage: Less Is More Good writing begins with a profound respect for words, their Specific Parts of Scientific Papers precise denotations, and their connotations. Do not use three Science writing is a unique process because scientific papers or four words when one will suffice. Every word of every sen- consist of specific elements that include the title, introduction, tence should work for maximum efficiency to achieve clarity methods, results, discussion, conclusions, summary, and and brevity, What looks like a natural gift to write is reaJly bibliography. Do not underestimate the importance of the great persistence, compulsiveness, and discipline. title. It is a clear statement of the paper's content and contains Along with brevity and clarity, accuracy is the third element key words that will be indexed for information retrieval sys- of good scientific writing. The words "scientific" and "data" tems. themselves suggest knowledgeable, documented, and orga- The introduction gives the necessary historical perspective nized information, Any manuscript should be written with the and then states why the work was done. It should seize the goal of its becoming a permanent and accurate record in the attention of the readers and emphasize the area of interest. scientific literature. Often the introduction is more effective if it is written last. Unfortunately, the structured methods and results are often Organization and Continuity written as rote copies of previous, similar works. This can re- Good scientific writing, then, is direct and definite. It suit in incongruities between these two complementary sec- demonstrates confidence and inspires confidence in your tions. The important point is to give the reader enough ac- readers. Weak writing, on the other hand, reveals uncertainty. curate information to allow a good understanding of how the One serious fault that weakens the reporting of careful sci- work was done and what the results were. entific work is the Jack of organization. Results reported in a In the discussion and conclusion, it is necessary to return disorganized manner take more time to interpret than readers to the argument you planted earlier in the introduction, Your are willing to spend. Without a well-organized presentation readers cannot be left seeing the trees but no forest. A comof the data, years of work and money may be wasted. parison of your work with others' and explanations of simi- For good organization, effort is required. For any subject, larities or discrepancies form the discussion, which moves to interrelationships should be addressed and then recapitulated a logical justification and conclusion of your paper. as they relate to otheT elements. Transitional sentences, which The writing of a summary follows easily. The summary is bridge thoughts, are often missing in poorly written pieces. composed of highlights of each preceding section, and though Inherent in good organization is continuity. Every sentence it often appears first as the paper's abstract, it is best written shouid connect the one preceding it to the one following it. last. Often neglected are explicit connectors that signal to the It is hoped that your readers will respond intellectually to reader that the direction of the argument is changing, being your information. Disagreement with your conclusions is far paralleled, or being contrasted to an earlier one. The signposts better than disinterest in ideas that are not clearly enough to use in these cases are conjunctive adverbs or brief transi- stated to be understood. The goal of all writing is to get a tional phrases that signal the thought coming next. The fol- message across. A well-written paper is a pleasure to read and lowing list offers a variety of choices for creating continuity a great satisfaction to the seeker of scientific information. and greater precision. Use them often. Common Pitfalls The hardest step for most writers is getting past the first This is publication no. 388 from the Eleanor Roosevelt Institute for draft. One must be able to say, "This wonderful creation of Cancer Research. mine still needs work." Compulsiveness is a trait of good 1 Present address of author: Health Data International, P.O. Box 2400. writers. When you think that you have a finished product, go Ketchum, iD 83340. back over it several times to check the specific points outlined

246 Journal of Chemical Education below which identify some of the most common errors and defined the first time they are used in your text. Some well- weaknesses. known abbreviations that are generally acceptable, but Read your manuscript through once, looking exclusively commonly misused, are given with their full meaning: at your subjects and verbs. Are subjects and verbs matched for singular and plural forms? Check that verb tense and form e.g., exempli gratias, for example-—Use commas before and denote conviction instead of doubt. Do not use constructions after and periods after each letter of the abbreviation. et al., et alii, and others—Since "et" is a complete Latin word, like "appeared to be" and "can be seen to" if verbs like "oc- do not use a period after it. The second word is abbre- curs" and "shows" would state the same ideas. The latter not viated, and a period must follow it. only result in more decisive statements but also use fewer i.e., id est, that is—As with "e.g.", i.e. must be set off with words. commas before and after and periods after each letter. Next read through your manuscript checking to see that viz., videlicet, namely—Also set this off with commas before each procedure described in the methods section was actually and after. performed and reported on in the results section. At the same Some Commonly Misused Words time, compare every figure and table to the statements attributed to them in the text Make certain that the text fully Affect-effect. "Affect" is commonly used as a verb that describes these illustrations. In addition, captions for figures means to influence and less commonly as a noun that means and tables should stand by themselves as brief explanations an artificiality. "Effect" is used commonly as a noun to mean of such visual representatives of the data. the result or outcome and less commonly as a verb that means Recall that brevity and clarity are essential. Do not use three to cause or to bring about. or four words where one will suffice. Why say "in the event Consensus. It is redundant to use the phrase a "consensus that" instead of "if"; "on the order of instead of "about"; "for of opinion" because consensus means a collective opinion. the reason that" instead of "since"; or "one and the same" Criterion-Criteria. Criterion is singular; criteria is plural. instead of "the same"? Other related words are medium-media, datum-data, and Finally, check the cited references to insure that they ac- stratum-strata. tually contain the material attributed to them. Do not rely on Different from-Different than. The preferred preposition references from similar papers. Typing errors are very com- after different is from; however, different than is acceptable mon among the numbers used in bibliographical informa- if it avoids a wordy clause. tion. Factor. This word resonates with scientific overuse; its synonyms—element, ingredient, and component—-are und- Odds and Ends erused. What follows is a catch-ail of various stylistic and proce- First-Firstly, "First" is a genuine adverb itself and should dural items that particularly plague science writing. be used without the suffix "-ly." "Second," "third," etc., fall Punctuation into this same category. Semicolons. A semicolon replaces a connecting word like Imply-lnfer. If an author implies something in his paper, "and" and can be replaced by a period; it is not a substitute something is hinted at; the reader infers or understands the for a comma. It is often used to combine two or more related hint. independent clauses. Another common use of the semicolon Like-As. In formal usage "like" should be used only as a is to separate items in a series. This is not a violation of the rule preposition. "As" is acceptable as both a preposition and a that each part must be a complete sentence; the form may be conjunction. viewed as elliptical, the missing words being understood. The Only. Make sure "only" is placed immediately before the writings of Mark Twain and G. B. Shaw abound with semi- word it is intended to modify. colons. An illustration of the use of semicolons in good scien- Principal-Principle. A rule or truth is a principle and it is tific writing occurs in the paragraph below (2) in which the used only as a noun. Its homonym, "principal," is a noun or words "These hybrids have been used for" are understood as adjective and means chief or leading. a common prelude to each phrase separated by semicolons: Revert back. Simply use "revert"; "revert back" is redundant. In this paper I review newer experimental developments in our Reason is bemuse, "Because" means "for that reason"; this laboratory, which are based on development of ausotrophic and is a common redundancy. other mutants of mammalian cells and the construction of a series of hybrid Chinese hamster ovary f CHO) cells containing sin- Thus-Thusly. "Thus" is an adverb by itself and needs no gle, or email numbers of, human chromosomes. These hybrids suffix. have been used for genetic, biochemical, and differentiation anal- Unique. There is only one of a kind of a unique thing. "Most ysis of eeli surface macromolecules; regions! mapping of particu- unique," "very unique," or "rather unique" events do not exist. lar genetic markers; an approach to biochemical understanding of Use "unusual" or "rare" in place of these incorrect terms. the human aneuploid diseases; a new method for detection of en- Everyone can develop skill in the use of language that vironmental mutagens and carcinogens; and an amalgamation of somatic ce53 genetic techniques with those of recombinant DNA conveys scientific information in a meaningful, persuasive, in order to devise a new method for mapping the human genes, and understandable manner. It is an accomplishment that is which promises wide application and high resolving power (2). learned and that grows by paying attention to good writing to see how these skills are used to their fullest. None of these Commas. Insert a comma where there is a light natural learned skiils are intended to conflict with an individual's pause. Reading aloud your words is the best way to determine writing style, which is a unique portrayal of the author's per- this. Conjunctive adverbs and signpost expressions like sonality. A natural writing style is the best and most plea- "moreover," "therefore," and "on the other hand," must be surable to read; such a style comes only with practice and a set off by commas both before and after if they occur in the desire to improve your writing. Two quotes, one from a sci- middle of a sentence. Never connect two independent clauses entist and the other from a well-known literary figure, sum by a comma; use only a semicolon. up these ideas appropriately. Colons, The colon, like the semicolon, joins related thoughts; however, it ia used only when the first thought in- When we encounter a natural style, we are astonished and de- troduces the second. Any colon used properly can be replaced lighted; for we expected to see an author, and we. find a man. by "that is" or "namely." Pascal (3) Abbreviations Interviewer: How much rewriting do you do? Hemingway: It depends. I rewrote the last page of Farewell to Abbreviations that have not become standardized must be Arms thirty-nine times before 1 was satisfied.

Volume 61 Number 3 March 1984 247 Interviewer: Waa there some technical problem there? What was Literature Cited it that stumped you? il) Flmcb, R., "the Art of Readable Willing," CoUiei Books, New York, [962, p. 148. Hemingway: Getting the words right. (2) Puek, T. T., Conltol of Cellular Division and Development; Part B, 393 (1981J. (3) Pa5Cai,"Pensoes,"SeeiionI,do.29. Ernest Hemingway (4| Hemingway, E.. "The Peris Review Interviews," Second seriea. Plimpton, G. (Ed.) Viking, interviewed by Geoige Plimpton (4) NewYork, 1965. p.m.

Scenarios in Science

Sharon J. Sherman and Alan Sherman Middlesex County College, Edison, NJ 08818

Many students who are nonscience majors are enrolling in of war and destruction and decided instead to pool their science courses today at both the high school and college levels. knowledge and wealth to improve the human condition. Many These students are interested in learning more than science of the problems that plagued human society in the late 1900's history and fact- They want to know how science and tech- were brought under control by 2025. Programs to stabilize nology are affecting them now and how it will affect them in population growth and produce adequate food for those living the future. A technique that we have employed while teaching on the planet were becoming effective. Medical science, as well nonscience majors at our school involves the uae of scenarios as the natural sciences such as biology, chemistry, and physics as introductions to the topics under discussion. These scen- reached new frontiers, arios are sometimes biased and may take either a positive or However, it was the discovery in this year of 2050 that was negative view of the subject matter. Most important, the to bring startling news to the scientific community. Scientists scenario gets the student involved in the topic and sets the and engineers had transplanted the brain of an individual into stage for an in-depth discussion once a particular chapter in an artificial body. The new body had the appearance of a the course has been covered. human being and functioned in a completely humanlike Here is our suggested method of operation. A scenario is manner. The transplant had been a success. The ramifications presented to the student in hand-out form at the time that a of this event were awesome. This new body would not age and new topic is introduced. The majority of students have not yet would last 200 years! begun to read the assigned chapter. A short discussion of the subject matter follows and students are allowed to ask ques- Scenario: The Day We Lost New Jersey tions pertaining to the topic. On many occasions it becomes It is a bright, sunny day in New Jersey on April 5,1990. New apparent that the students are not familiar with the subject Jersey has grown through the years to become a major in- matter and are not able to discuss the issues raised by the dustrial state in the northeast; a state that consumes a tre- scenario. The students clearly see the need to read the text mendous amount of industrial power. Almost 80% of this assignment, as well as any supplementary material avaiiable, power is supplied by ten nuclear power plants located either and attend the lectures so that they will be able to participate in the state or surrounding it. Two of these power plants are in an in-depth discussion of the scenario upon conclusion of off the coast of Atlantic City, built on manmade islands in the the topic. Atlantic Ocean. New Jersey is not a state that is prone to many What follows are examples of three scenarios that we use natural hazards, Tornados, hurricanes, and earthquakes are in our nonscience majors chemistry course. The first scenario infrequent. That is why it came as such a complete suprise is entitled "New Bodies for Old." It is used as an introduction when on this day a major earthquake hit the state, sending to the course when discussing the impact of chemical science shock waves from Boston to Virginia Beach. The quake was and chemical technology in today's world. The second scenario as strong as the one that devastated the city of San Francisco is called "The Day We Lost New Jersey." It presents a in the early 1900's. However, in New Jersey the results were somewhat biased view of nuclear energy and serves as an in- more devastating. The earthquake demolished numerous troduction to the topic of nuclear energy and nuclear power. buildings and tore up many roads. The quake was centered We must point out, lest we offend the proponents of nuclear on the central Jersey coast, not a highly populated region. power, that although this particular scenario appears some- Large numbers of people were not killed by the initial devas- what one-sided, it is quite successful in getting the students tation- The problems arose with the four nuclear power plants involved in the subject matter. A well-balanced view of nuclear located just off the coast and with those located on the coast energy is presented in class. When students have read the of the Jersey shore. assigned material and attended lectures, they have sufficient Although these plants were supposed to be earthquake- information to allow them to make their own decisions re- proof, they were not strong enough to withstand the power of garding nuclear power. this quake. Sections of these power pianis broke away. Cooling The third scenario entitled "Starting Off Right" is used to systems were lost and the atomic cores heated to meltdown. introduce the subject of food chemistry. The scenario deals Radioactive clouds of steam were dispersed into the atmo- with the topic of infant formula versus breast milk. As you sphere. Offshore breezes blew the clouds across the state. read these short scenarios, keep in mind their main purpose Tens-of-thousands of New Jersey residents died of the effects which is to whet the student's interest and foster involvement of this radiation and tens-of-thousands more were to die of in the subject matter. radiation-linked diseases.

Scenario: New Bodies for Old Scenario: Starting O(f Right The year is 2050. During the first fifty years of the 21st It is the year 2010; a step into the 21st century. A baby has century science and technology were used by the governments just been born and has been given to her mother to be fed. The of the earth to improve the quality of life on this planet for all baby is being breast-fed and a natural process is taking place people. It was the year 2000 when the major powers on this once again. The mother is relaxed and comfortable and the planet agreed to stop spending billions of dollars in weapons baby is being weil nourished.

248 Journal of Chemical Education Toward the end of the 20th century, during the last few scenarios are in many cases one-sided, and designed specifi- decades, a trend toward artificial feeding of infants was seen. cally to promote discussion. After studying nuclear power it In the industrialized countries of the world substitutes for might be a good idea to plan a nuclear power plant discuasion breast milk became easily available. Millions of mothers gave session. Students can choose or be assigned pro-nuclear or their infants formulas made from pasteurized cow's milk. anti-nuclear sides. They then present their views in a debate These babies showed a fine pattern of growth and weight gain. or planned discussion session. Students wili see that the group But experts learned that breast milk was better. It provides armed with the greatest amount of research material and fads the infant with some forms of immunity to disease. It is more will be able to argue a stronger case. Students might also try easily digested and it rarely causes an allergic reaction. Breast to write their own scenarios to demonstrate another point of milk also contains a natural laxative. view on some of the other topics. Problems arose with artificial feeding in many of the Middle There are several uses for this teaching too! in science ed- Eastern and African countries and in South and Central ucation. It can be the basis of a one-semester course at the high America, as well. Largely as a result of commercial advertising, school level called "Decision Making in our Technological urban women of these countries abandoned breast-feeding Age." Here students would be presented with the various and swtiched to milk formulas. In the absence of absolutely issues facing us today and learn how to evaluate these issues. safe drinking water, good sanitary conditions, and refrigera- Another use at the high school level is the application of this tion, baby formulas sometimes became carriers of common technique to add relevance to the topics studied in science infections. This caused several diseases which were once seen class. After scientific principles are learned, the instructor can mainly in older children to be seen in infants. Re-education point out the applications of these scientific principles and of the population as to the values of breast-feeding reversed discuss the issues which have developed as a result of these this trend. Even an undernourished mother is able to produce technological advancements. Finally, we use this technique 400 to 600 ml of milk daily for her child. In the year 2010, this in our college level nonscienoe majors course to introduce and is the more advisable method of feeding infants throughout motivate students in chemistry and teach about the deci- the world. sion-making process. As we progress in the area of science education it is clear Using the Scenarios that science courses for nonscience majors and high school After reading these introductory scenarios, the student students which present only science fact are not sufficient. realizes that in order to understand and discuss a science- While understanding concepts is central to learning and un- related issue, the scientific concepts behind the issue must be covering new information, the effect of science on humanity studied. At this point the instructor begins the lecture mate- is of significance. The students of today who will be the leaders rial. The six basic questions—-who, what, where, when, how, of the future must have a clear picture of how scientific dis- and why—will be answered in the lecture and lead to an un- coveries can affect us both positively as well as negatively. derstanding of the topic. The instructor must be careful to Only in this manner will they be able to make logical decisions point out to the students that their opinions must not neces- based primarily on fact and not on emotional persuasion. sarily agree with the view presented in the scenario. The edited by MARY VIRGINIA ORNA, O.S.U College of New Roeheite thumbnail /ketche/ New Roehelte, NY 10801

Is Sugar from Sugar Beets the Same as Sugar path involving the three-carbon intermediate phosphoglyc- erate {!), and a more recently established path involving a from Sugar Cane? four-carbon dicarboxylic acid intermediate (2). Plants are W. Conard Fernelius divided rather sharply into two classes, designated C3 and Cj Kent Stale University according to the number of carbon atoms present in the Kent. OH 44242 photosynthetic intermediate. The selective rejection of 13C

is greater by the C3 pathway than by the C4 pathway (3). If At the beginning of this century when the beet sugar in- 513C equals the difference of the ratio of 13C to 12C, times 1000, dustry in this country was relatively young, there were those in a sample and the ratio in a reference standard marine car- who insisted that cane sugar was different from and superior bonate, then 513 for atmospheric carbon dioxide is —7, the to beet sugar. Chemists took no stock in the arguments be- average for C3 plants is -26.5, and for C4 plants, —12,5. Now, cause to them it was obvious that a pure compound was the sugar beets are C3 plants and sugar cane a C4 plant. So a mass same regardless of the source. Nevertheless, it actually is spectroscopic examination of the products of combustion will possible to tell whether a given sample of sugar came from indicate the source of the sugar. cane or from beets by means of a mass spectrometer, an instrument now in common use in most laboratories, since the Since bees gather honey from C3 plants and corn syrup 13 12 ia 12 ratio of isotopes of carbon C to C is different in the two comes from C4 plants, a measurement of the C/ C ratio of. kinds of sugar. a sample will show whether it is pure honey or one diluted with low-cost, high-fructose corn syrup (4), Similarly, knowledge These two stable isotopes of carbon normally exist in the of the ratio will indicate whether a glass of orange juice is the ratio 1.104 to 98.892. (For present purposes we can forget real thing, which has a large negative shift in (3C/12C, or a about the minute amounts of 14C whose weak radioactivity synthetic one made from orange pulp, artificial flavoring, and makes carbon dating possible.) In the products of photosyn- high-fructose corn syrup, with a smaller negative shift in thesis the ratio of 13C to 12C is slightly less than their ratio in i3Qf\2Q (5)_ Archaeologists are even using 513 values of bone the COa of the atmosphere. Such isotopic selectivity is known collagen to reconstruct the diets of ancient man (3,6). for many reactions. However, the conversion of CO2 to carbohydrates in plants takes place by two routes: the familiar Literature Cited (5) Calvin, M., and Benson, A.. Science, 107,476 [1948). (2) Kortshacii, H. P., Hsrt, 0. E., and Bun, C. 0.. Plant Phyaiol.. 41), 909 (1966), Brief descriptions of phenomena, topics, and tacts which chemical (3) van dcr Merwe, N. J., Amur. Sei., 70,596 «983). educators have found to be of interest in their teaching, are presented (4) White, J. W., and Covet, L. W,, J. Amoc. Off. Anal. Chem., «1,746 0978). in a "note type" format throu^oul the JOURNAL. <5) .liihualon.K; Science B2, (October), 86 (1882). (6) Zurer, P. A., Chtm. Eng. News, Peb. ai, 1983, pp. 33,36.

Volume 61 Number 3 March 1984 249 edited by MIRIAM C. NAGEL /ofety tip/ Avon High School Avon, CT 06001

Peroxides Can Be Treacherous On the question of possible unstable, unwanted peroxide Miriam C, Nagel contamination of a reagent, one is wise to err on the side of safety. There are tests that will detect the presence of perox- Avon High School Avon, CT 06001 ides. However (6),

Peroxides are unstable, shock-, thermal-, and friction- Any suspect material will be in some kind of container. If there is sensitive compounds whose sensitivity increases with con- a deposit of sensitive peroxide in and around the cap of that container, the act of removing the cap—in order to obtain a sample centration. Organic peroxides are ail highly flammable. High to test for the presence of peroxide—may initiate tie detonation school teachers need to be aware of the possibility of peroxide of the peroxide. This test, though reliabiy positive for the pres- formation in aging organic solvents and stored alkali metals. ence of peroxide, yields undesirable results. Therefore, a first "A peroxide present as a contaminant in a reagent or solvent principal policy statement; can change the course of a planned reaction" (1). That change If 1 think I ought to make a test for the presence of peroxide can be a violent explosion. then I have already kept it too long; instead of testing 1 should as- In normal oxides each oxygen atom has a -2 oxidation state. sume as certain that unstable peroxides are present and dispose In peroxides two oxygens form a nonpolar covalent bond with of the material in a suitable manner. a net —2 oxidation state (2). The oxygen linkage (—0—0—) Life would be much easier if there were a list of peroxide of the peroxy group in some organic compounds is actually formers and reliable information on how to store them safely. useful when properly handled. The (—O—O—) bond splits, Unfortunately, the problem is too complex for the simple so- producing free radicals which can initiate polymerization. This lutions. CHAS Notes f 7) offers some suggestions on potential instability makes them useful in polymer industries (3). But peroxide formers. One such list includes organic compounds industrial settings are far removed from first year chemistry with these structural components (examples are illustrative, courses. Some peroxides are so sensitive they have no com- not definitive); mercial value. Different peroxides vary in their degrees of hazard, de- ethers, acetaJs, secondary alcohols, oxygen pending on the structure of the compound and the concen- heterocycles tration of the active oxygens. Dangerously reactive peroxides can build up in old solvents such as diethyl ether and isopropyl olefins with aliylic H, terpenes, ether. Half-empty containers of ether can form treacherous tetrahydronaphthalene peroxides from autooxidation. Peroxides of this type are more isopropyl compounds, shock sensitive than TNT. Any purchase of ethers for use in decahydronaphthalenes a high school has to be questioned. Where the high school needs to be especially concerned is in the accumulation of unwisely purchased solvents such as ethers, or alkali metals ally! compounds such as potassium, in which dangerous peroxides could be accumulating. Even hydrogen peroxide should be handled with extreme haloalkenes, vinyls care, particularly the 30% solution commonly found in high school labs. Besides being a very strong oxidant, contamination of the H2O2 from metals and meta! ions can cause violent dienes decomposition reactions as targe quantities of oxygen gas are I generated. Diiute hydrogen peroxide mixed with dilute acetic H H acid forms explosive peracetic acid when heated to 110°C. vinylacetyienes Hydrogen peroxide mixed with organic matter under some circumstances has the same explosive power as an equivalent H weight of TNT (4). —C---C cumenes, styrenes f I -Ai One high school chemistry teacher inherited a bottle of H cyciohexene that had been in the stockroom for at least a decade. The teacher, new to the school, noticed crystals in the aldehydes bottle and suspected peroxide formation. The problem was H reported to school authorities. After some persuasive conversation, they took the problem seriously. A phone call to the N-alkyl amides, ureas, lactams state police was made to have the bottle removed. The police T T checked with chemical safety experts and were convinced of Other compounds and elements; the hazard. When school was not in session, the police removed the bottle with the same care as a suspected bomb alkali metals potassium (5). alkali metal alkoxides and amides sodamide organometallics Grignard reagents Regarding the problem of storage, as noted above, high "Safety Tips" presents safety Information and practical suggestions to school teachers should carefully weigh the merits of getting meet the special needs of high school chemistry teachers. H is also a involved with peroxidizable reagents before ordering supplies. forum in which teachers can share their experiences and seek solutions Does the benefit justify the risk? It is hard to imagine any to safety related problems. situation where a safer experiment, a good film, or even a challenging problem for the computer would not suffice to

250 journal of Chemical Education teach the principles involved at the high school level. If 5) Avoid all potential for friction or impact hazards. No chemicals prone to peroxide formation must be purchased, grinding! limit the order to the minimum amounts required. Then, 6) Do not use glass containers with screw caps or glass stoppers for "store peroxide formers out of heat and light in closed vessels, storage. Use polyethylene bottles with screw caps. perferably in the container furnished by the supplier... [and] In a high school lab, where the naivetS of students can make keep no peroxide formers on hand longer than two months" any experiment risky, peroxide problems are best avoided by {7). avoiding the chemicals that can produce them. If a high school teacher has to handle peroxides or potential peroxide formers, a few cautions for handling them should be Literature Cited followed (8): (1) Natbnal Research Council, '"Prudent Ftactices for Handling Hazardous Chemicals in Laboratories," National Academy Prese, Washington, UC, 1981, p- 63. {21 Timm, John Arrend, "Genera! Chemistry," 4th ed., McOra»-HUl Book Co., New Yolk, 1) Unused peroxides should never be returned to the container. im p. us. 2) Clean up organic peroxide spills immediately with vermiculite; (3) Varjavflndi, Jr, "Safe Handling of Organic Perosidea," m "Safety in the ChenricaJ Lab- dilute the waste to a concentration of 2% or less, then transfer oratory." Vol. 3, {Editor: Steers, Nurman V.|, J. CUEM. EDUC, Eaaton, PA, 1974, p. to a polyethylene screw-top container containing an aqueous US. soiution of a reducing agent such as ferrous sulfate. HI "Hazardous Materials," 4th ed., National File Protection Association, Boston, MA, 1972, 3) Never concentrate by evaporation or distillation. IS) "Safety Tips," J. CHEM. EDUC, 59,156 U982). (6) CHAS Notes, 1(4], 1 (1982). American Chemical Society, Division of Chemical Health 4) Do not use metal spatulas; instead, use ceramic oi wooden anil Safety, Washington, DC 20036. spatulas. This caution is particularly important for those using (7| Reference (St, p. 3, alkali metais. (SI Referenced),p.64. edited by GEORGE L. GILBERT Denlson University te/ted demonstration/ GranviHa, Ohio 43023

Diffusion of Gases—Kinetic Molecular Theory of may wish to discuss gas densities at this point) and try it again. This time the wash bottle does not squirt since the beaker has Gases air in it. SUBMrrTED BY K. D. Schtecht Problems S.U.N.Y. BrocKport, Brockport, NY 14420 The porous cup must be dry. A wet surface slows the dif- CHECKED BY fusion sufficiently to prevent the bottle from squirting. If the David Speciehard porous cup gets wet, oven dry it for several hours. Also, if the Loras College, Dubuque, 1A 52001 water level in the wash bottle gets too low, the demonstration The pressure inside a container with a porous surface can does not work wefl. be changed due to the rate of diffusion of low molecular weight Hazards gases. Hydrogen is flammable, Helium is much safer. Materials Discussion Plastic wash bottie (250-ml or SOO-ml) Porous cup {such as Coors #60495 or 70001 or Sargent-Welch Low molecular weight gases diffuse or effuse more rapidly #S-43755OA) than do heavy gases. (Kinetic Molecular Theory of Gases says Rubber stoppers and glass tubing two gases at the_same temperature have the same average Cylinder of Ha or He kinetic energy, KE = '•famv1, so light gases must have higher 600-ml beaker average velocities and hence diffuse faster,)2 Thus, when the beaker is held over the porous cup, Ha or He goes into the cup Procedure faster than the other heavier gases (air) can leave, thereby Hook up the wash bottie and porous cup with the stoppers creating a positive pressure. Measurements made on this and glass tubing as indicated in the figure. Fill the wash bottle system with a manometer indicate that the pressure inside the with water, but not so full that siphon action would begin. A porous cup can increase by almost 0.25 atm within 10-15 s. dye such as methylene bine may be added to improve visibility The process described here occurs due to the difference in from a distance. Pill an inverted beaker with hydrogen or concentration of H2 or He on the two sides of the porous sur- helium gas. Place the inverted beaker over the porous cup. face. The pressure difference between the two sides of the Water should "magically" '• begin to squirt from the wash porous surface should drop to zero after the concentration of bottie. Lift the beaker, and it stops. Repeat the procedure. H2 or He is the same on both sides. Again manometer mea- Empty the beaker of the gas by turning it right side up (you surements verify that the pressure drops slowly to atmospheric pressure. Within 1-2 min, 90% of the peak pressure is lost If the H2- or He-filled beaker is removed after it has been over the porous surface for more than a minute, the pressure difference is immediately reversed as H-j or He dif- fuses out of the cup, creating a negative pressure. Air bubbles are observed entering the wash bottle through the spigot. Of course, in a short time equilibrium will again be established and no pressure difference will exist.

1 A digression on the difference between "magic" and a scientific demonstration: In magic one tries to deceive the audience by sleight of hand, but in scientific demonstrations, one uses laws and theories to explain observations. It would be very easy to perform this demonstration as a magic irlck If the gas cylinder and its tubing were con- cealed. 2 Boikess, R. S., and Edelson, E., "Chemical Principles," 2nd ed., Harper & Row, New York, 1981, pp. 113-116.

Volume 61 Number 3 March 1984 251 Chemical Storage of Solar Energy Using an Old Color Change Demonstration

L. Gene Spears, Jr. Rice University, Houston, TX 77005 Larry G. Spears University of Houston Downtown, Houston, TX 77002

One of the major problems associated with the utilization of solar energy as a primary energy source for heating and cooling is the lack of a practical, efficient means of storing large amounts of energy after it has been collected (I). Below we describe the results of a student research project that could be used as a class or group experiment at the high school or first-year college level to illustrate the potential of hydrated salts for solar energy storage. It involves a demonstration often used to illustrate the ease with which some transition metal ions can change their coordination numbers (2). The demonstration requires a solution, containing approximately 10 g CoCla-6H2O per 100 mL of isopropyi alcohol, that has been made distinctly pink by the dropwise addition of water. At room temperature, the pink color of the solution is due 1!+ to the octahedral complex, Co(HzO)g , On heating in a hot •wo 600 600 700 water bath, the solution changes to a deep bine color due to Wavelength (nm) the formation of the tetrahedra! complex, CoCU2". This system can be described by the equation Figure 1. The i/islbie spectra of Co^Ofe** and CoCU2".

2 Co(H;O)6 + + 4C1- + heat — CotV~ + 6H2O pressions for a system with two absorbing species (4). A Since this reaction is endothermic, it provides a potential 2 spectrophotometric scan of both the pink and blue solutions means of storing solar energy via the unhydrated CoCL) " ion. indicated a. maximum absorbance of the pink complex at 513 On cooling (the reverse reaction), energy would be released nm and a maximum absorbance of the blue complex at 655 ran based on the heat of hydration and the specific heat of solu- (see Fig. I). Calibration plots of absorbance versus moSarity tion. 2 2+ were made for CoCU " at 513 and 655 nm and for Co(H2O)6 To determine the potential capacity of this system for solar at 513 and 655 nm, using a cell pathlength of 1.0 cm, and the energy storage it is necessary to know the following: (1) the following molar absorptivity values determined (P = pink solubility of C0CI2 in isopropyi alcohol at different tempera- complex and B = blue complex) tures, (2) the heat of hydration for CoCL,2-, (3) the specific heat of the solutions, and (4) the effects of HSO and Cl" on the a(L/mole-cm) equilibrium system. Based on these data and published data 513 nm as' = 18.0 op' = 5.46 on solar energy systems and energy use, calculations can be 655 nm aB° ™ 491 ap" = 0.60 made to determine the amount of CoCl2-6H20/isopropyI al- coho! solution that would be needed to store the necessary Since the mo!ar absorptivity constant op" is very small energy required for a average residence in the United States. compared to

2S2 Journal ol Chemical Education .72 Added H-O Cone • O.OOOM o 0.1 S4M • 0.183M .60 . i 0.218M 0.400M

.48 -

8 -36

.34 -

o hag Soiy. - 0.086T - 0.87 ALogSaly.«0,062T-1.33 33 40 48 Temparsture, "c

! a+ Figure 3, Effect of temperature and HaO on the CoCi, ~/C

30 4B Temperature, C Figure 2. Logarithmic plots of ttie solubility of CoGirlfy&k in Isopropyl alcohol/H;0 solutions at different temperatures.

ments, and then added to obtain the total concentration of dissolved cobalt chloride. The results of these measurements are shown in Figure 2.

Determination of Product/Raactant Ratios For the reaction in this study the equilibrium constant expression can be written as

"en ~" '

Due to the difficulty in measuring values for the free water concentration in this system, values for the ratio [C0CI42-]/ 2+ [Co(H2O)e l were used instead of Kev Figure 4, Effect of H O on the CoCUi~/Co(H OJ s+ ratio. 2 5 s B Effects ofH20 on the CoCh "iCo{H20)

Volume 61 Number 3 March 1984 253 Determination of Specific Heat Volume of Energy Storage Solution Needed The specific heat describes the amount of heat a particular For these calculations it is assumed that the energy storage solution can absorb. A solution of 0.1 M cobalt chloride in solution is circulated only once in a 24-h period and that the isopropyl alcohol was selected as representative for this study, temperature of the cooled solution is 20"C and that of the and a double-walled expanded polystyrene, student-type heated solution is 60°C. The heat absorbed per liter of the calorimeter used for the measurements (5). A value of 3.37 solution is J/g/°C was determined. 81.5 kJ/L + 2.67 kJ/°C/L X 40°C = 188 kJ/L Determination of the Heat of Hydration of CoCk Since the amount of heat needed per day is 2.89 X 108 J/day, The major reason for considering a hydrated salt system for the required volume of solution needed per day is energy storage is that the heat of hydration associated with 6 the salt can store and release larger amounts of energy than (2.89 X 10 kJ/day) X (I L/188 kJ) = 1537 L/day just the specific heat associated with the heating and cooling = 1.067 L/min. of a liquid such as water. Using a modified Nalgene® Dewar flask with cover for a calorimeter and a previously reported Volume of Storage Tank Required method for determining the heats of hydration (6), a value of The volume of the heat storage tank required to store a 92.7 kJ/mole was obtained for the heat of hydration of CoCl2- one-day supply of heat using the above conditions is thus 1537 This value is higher than a reported literature value of 76.8 L or 1.537 m3. If a 50% efficiency factor for heat storage is as- 3 M/mole for the heat of solution of CoC!2 {7), and a value of sumed, a 7.9-m tank could store a three-day supply of energy. 89.4 kJ/mole calculated based on the heats of solution for If only water were to be used for energy storage under these 3 CoCl2 and CoClr6H20 (8). conditions, a volume of 10.4 m would be required. Obviously, if the solution were circulated faster than L067 L/min, more energy would be available and thus a smaUer storage volume would be required. Circulation rates of 10-40 L/min are commonly used for aqueous systems. Energy Calculations Some basic properties of a solar heating system using cobalt Solar Heat Collector Surface Area Required chloride as a heat storage medium were calculated based upon Assuming that the solar collector is exposed to 2.05 X 104 data collected in this study and from various published doc- kJ of heat per square meter of surface area per day, an ac- uments. cepted figure for the southern United States (3), the available solar energy per square meter per minute would be 14.2 kJ. Daily Heat Energy Requirement for the Average U.S. Earlier we found that 2.89 X105 kJ/day, or 200 kJ/min, of heat Residence are needed for the average residence. Assuming a 100% col- Assuming that the average U.S. residence of 1500 ft2 re- lector efficiency, the area of collector surface needed is quires 1000 therms of heat per year (3), the daily heat requirement is (200 kJ/min) X (1 m2 rain/14.2 kJ) = 14.1 m2 (1000 therms/yr) X (1.055 x 108 J/therm) Assuming a more realistic figure of 50% efficiency for the s X {1 yr/365 days) = 2.89 X 108 J/day collector, 28.2 m of collector surface area would be required. Using a 4:1 heat concentration ratio and a 1:6 collector tubing Concentration of Cobalt Chloride area to collector surface area ratio, 42.3 m2 of collector area would be needed for the solar heat collector. The solar collector was assumed to concentrate incoming heat at a 4:1 ratio, and to operate at a mean temperature of Possible Oil Dollars Saved by Using a Solar Heating System 60°C. Using Figure 2, the concentration of cobait chloride in a saturated solution of 100% aieohoi was determined to be Assuming that the residential heating requirements for the 10.47 M at 60°C. above residence are obtained only from imported oil, the oil dollars saved by using only solar energy would be Heat Content of Solution (1.066 X 10" J/yr) X (1 barre!/3.06 X 10s J) The heat content of the solution is due to both the heat of X ($34/barreI) = $1,184 hydration and the specific heat. In Figure 3, it is seen that for z 2 100% alcohol at 60°C, the CoCU ~/CoiHzOh * ratio is 0.64 Literature Cited and at 20°C it decreases to 0.44. Prom these values it can be D (1) Wentwonh,W.E.,etal.,.9«iar,W£yr2S, 141(1981!, determined that at 60°C, 39% is unhydrated, and at 20 C, (2) Chen, Philip S,, "Entertaining and Educational Chemical Demonstrations." Stockton 30,6% is unhydrated. Thus on cooling from 60°C to 20"C, 8.4% Trade Press, Sanla Fe, CA 1974, p. 36. of the CoCl42~ undergoes hydration. (3) Ijiftness, Hubert L., "Energy Handbook," Van Korstrand Reinhold Co., New York, 1978. (41 Friln, James 8., and Schenk. Goorge H., "Quantitative Analytica! Chemistry," 4th ed., (92.7 kJ/moie) X (10.47 moles/Li X (0.084) * 81.5 kJ/L Atiyn and Bacon, Boston. 1979, p. B2. 15} Morss, Lester It, and Hoikees, Robert 8., "Chemical Principles in the Laboratory," The specific heat of 1.0 L of a 10.47 M solution is approxi- Harper & Row, New York, 1978, p. 84. (6) Shiftet.t, B. B., J. CHKM. SDUC, SS, 103 (1978). mately 17) "I-ange's Handhook of ChemiBtiy," ll£hedr,££&"£wvDean,<]ohn A,) MfSraw-Hill. ppr 9-108. (3.37 J/g/°C) X (0.793 g/mL) X (1000 mL/L) = 2.67 kJ/DC/L (8) "Chemical Engineer's Handbook," 6th ed., McGraw-Hffl, p, 3-147.

254 Journal of Chemical Education edited by ROBERT REEVES MaMOofough Schpo 250 S. Ftossmore Avenue filtrate/ A re/idue/ Los Angeles, CA 90004

Spectrophotomeiry: Mechanics and 5) Repeat the above process, in increments of 50 nm, until a wavelength of 800 nm is reached. Record the data obtained. Measurement 6) By looking over the data, determine the wavelength regions Susan M. Dtehi-Jones where a peak of absorbance (minimum %T) occurred. In these Broker Rioe High School regions, scan {repeat steps 3-5) tiie solution in increments of 10 7101 Lahssr Road nm. Birmingham, Ml 48010 7) Again, where a peak of absorbance occurs {minimum %T), scan the solution again; first in increments of 5 nm, and then in in- Pur (lose crements of 2 nm, to determine the exact wavelength of mini- This experiment is designed to be an introduction to spee- mum transmittanee. It should be noted that the regions scanned tiophotometry and to general spectral analysis techniques. in these smaller increments should only be less than 50 nm. This Students will become acquainted with the basic components entire procedure is called scanning a spectrum, of a spectre-photometer and their functions, will use a spec- 8) Calculate the absotbanee from the percentage iransmittance trophotometer in an open-ended experiment, and will me data and graph the results (absorbance versus wavelength). This graph is known as an absorption spectrum. Beer's Law in several different ways. In addition, they may compare the detectability (tolerance) of the spectrophotometer with visual detection limits as an optional activity. Abbreviated Procedure: Calibration Curve/Beer's Law The concepts involved in these experiments are not new. 1} Using volumetric flasks, pipets, and distilled water, prepare a The arrangement and method of presentation is, however, series of solutions of yoar "unknown" from a stock solution thought to be unique at the secondary level. identified by your instructor. (Instructor's Note: Usually I'M stock solutions are used.) At least four solutions of varying Equipment concentrations should be prepared; for example, 0.1 M, 0.36 M, 0.50 M, and 1.0 M solutions might be considered a series of Speetrophotometer standards. Be sure to record solution preparation methods in Pipets (1-inl through 25-ml, in 5-m! graduations) your notebook. Volumetric flasks f 100-ml) 100-200 ml of stock solution for each unknown (see special 2) Prepare tlie speetrophotometer for use, as directed. notes) 3) Adjust the wavelength selector knob to the maximum absorption peak determined in the Absorption Spectrum Procedure, which Procedure will be called the optimum wavelength, if two strong absorption peaks occur, choose the wavelengths nearest 300 nm, that is, Because of the open-ended nature of these experiments, choose the wavelength nearest the center of the visible spectrum, students do not necessarily need a detailed, step-by-step rattier than at one end. procedure. They may only be given a general procedure and 4) At this optimum wavelength, determine the percentage trans- an "unknown" solution. Both the general procedure and one mittanee for each prepared solution as well as for your unknown. abbreviated step-by-step procedure are given in the following Record the data. (The reference solution should be distilled sections. water.) 5) Calculate the absorbance from your percentage transmittanee Spectrophotometric Determination of the Concentration of data. Graph the results, absorbance versus concentration for an Unknown Solution all the standards prepared. This graph is known as a calibration curve or a Beer's Law plot. General Procedure 6) Prom the linear relationship graphed, read the concentration of your unknown. Record this concentration and report it to your Students first determine the wavelength of maximum ab- instructor. sorbance of a colored "unknown" solution by scanning. They prepare a series of solutions of this "unknown" of varying Limits of Detectability (Optional) concentrations (0.01-2.0 M). These solutions are from this point referred to as standards. Then, at the optimum wave- General Procedure length (identified earlier), students determine the absorbance Students prepare several solutions (10-20) of varying of each of the standards. Subsequently, the calibration curve concentrations of their "unknown" ranging from very dilute is prepared by graphing the results of absorbance versus to very concentrated and determine the absorbances at the concentration. Using this graph, the students apply Beer's optimum wavelength. To determine the limits of detection, Law to identify the concentration of the original "unknown" the students continue to vary the concentration of the solu- solution. tions until a concentration is reached which exceeds 85% transmittanee (lowest iimit) or transmits less than 20% (upper Abbreviated Procedure: The Absorption Spectrum limit). These two concentrations, then, are identified as the 1) Prepare the speetrophotometer for use, as directed. limits of detectability for the unknown substance. 2) Fill one cell with distilled water and the othei cell with your colored "unknown" solution. 3) Adjust the wavelength selector knob to 350 nm; determine the Abbreviated Procedure: The Limits of Detectability percentage transmittanee of your unknown solution at this 1) Prepare 1 M, 0.10 M, and 0.03 M solutions of the chemical wavelength. compound you studied previously. Record preparation methods 4) Record the wavelength and corresponding percentage trans- in your notebook. mittanee obtained. 2) Prepare the speetrophotometer for use as directed. Adjust the wavelength to the optimum wavelength determined in the Ab- sorption Spectrum procedure. New lectures and laboratory experiments and directions in teaching 3) At this optimum wavelength, determine and record the per- Chemlslry through 1he use of the faboratoiy are provided in this feature. centage tcansmittanee for each prepared solution. The reference Experiments wilt be fully detailed and wili be field tested before they are solution should be distilled water. [xibiished, Contributions should be sent to the feature editor. 4) If needed, prepare more dilute solutions and fepeatthe measurement procedure (step 3) until a solution concentration is

Volume 61 Number 3 March 1984 255 Limits of Detectablltty {Student Data) for CofNOsfe • 6H2O

wavelength * X « 512 nm sllt = O.OS mm (fllulion preparailon % abscwftance trom 1 M solution molarity OVC T tcalc) colOr

5 ml-10 mi 0.5 M 0.38 2.42 dk.red 3ml-10m! 0.3 M X 3.39 1.47 red 2rnl-10ml 0.2 M X 8.12 1.09 red 17ml-100fnl 0.17IW X 15.8 0.801 It. rad IS ml-100 ml 0.1SIW X 23.5 0.S29 ft. red 12rnMO0ml 0.12 M X Z2.0 0.6E8 It. red 10 mM 00 ml 0.10 M X 31.2 0.505 It. red 5 ml-100 ml 0.06 M X 61.2 0.213 pink 500 600 3 ml-100 ml 0.03 M X 74.7 0.127 pink ; mi-100 ml 0.02 M- X 86.9 0.061 WOVE LENGTH dial ft. pink Graph of absor&ance versus wavelength for deterrhlnlnQ the optimun wavelength 1 mM00 ml 0.01 M X 96.3 0.016 pals pink • 6HjO, 0 = opaque c- dear (not visibly dstedabla) reached, that, when tested, transmits 80-85% of the light. This V" visibly detectable detectable Smite (spectrophotometrlc) solution represents the iower limit of detection concentration. 3) This instructor scanned the. solutions listed on a Beckman 5) If needed, prepare more concentration solutions and repeat the DB-G. The data obtained, with the corresponding abaorbances, measurement procedure (step 3) until a solution concentration was available for comparison as a set of "theoretically-accepted" a reached, that, when tested, transmits only 15-20% of the light. values. Therefore, errors were quickly identifiable. The most This solution represents the upper iimit of detection concen- common student errors are: (1) dilution errors in either calcu- tration. Be sure to record all data, including the solution prep- lation or volumetric equipment usage and (2) the choice of a aration method. minor absorption peak (on one end of the visible spectrum) as 6) In order to make a comparison between the instrumental de- the optimum wavelength. Students find it helpful to develop tection limits and the visual detection limits, note the color and a computer program to calculate ahsorbance and print out the shade of each solution tested. data calculation. 7) Calculate the absorbance from the percentage transmittance The only disadvantage of the experiment is the extensive data for each solution tested, and put m tabular form with the solution preparation required. The feet that it k an introductory corresponding concentrations (in molarity). experiment does mean that student* may do more retrials than 8) (optional) Plot the data (absorbance versus concentration) to is usual for an experiment. However, in spite of this, all students determine whether Beer's Law is obeyed over the entire range seem to fiad the experiment interesting and a bit of a challenge, of conceotrations tested. and are able to complete it wetl within eight hours of laboratory time.' Special Notes Editor's Note: To obtam further information on student handout 1) This experiment offers the students the opportunity to explore materials, laboratory procedures, and DB-G ("accepted values") data, spectiophotoraetry whiie gaining the experience, practice, and contact the author directly. confidence necessary for independent research. Although students are not usually given a detailed, refined procedure, they Literature Cited are given the general instructions presented here, along with a (1) One or more equipment manuals for the spwtrophotometer in use. For elample, in list of background articles 1,1-9). Therefore, this experiment usiflfi Spectronic 20: Bausch and Lomb, Analytical Systems Division, "SpectrophO' would be especially useful in an AP or second-year chemistry b>n»eter EducationalU Manuel" Ow date). class. Other references appropriate for the instructor and/or (2) BeckmanInatruniemfi| AnIn<^ucU™toSpectmphotDBiet^,"8iulatfo student are listed below (10-20). California, Beckman Instruments, {No date). 2) The preparation for this experiment is extensive the first time, (3) Davis, Jeff C, Chtmictry, 50 (November, 1977). The entire series of articles (3-9) is available as Chemistry reprint 128, "Introduction to SpBctroscopy" from the since all accepted values must be determined experimentally. American ChemicaL Society. On a modem spectrophotometer (like the Beekman DB-G), (4) Davis, Jeff C, Chemistry, 48,3-9 (December, 1B75). where manual and automatic scanning can be done inter- <5) Davis. Jeff C, Chemistry. 48,15 (July-August 1875). (B) Davis, Jeff C, Chemistry, 4*. IB (May, 1975). changeably, the absorption spectrum of several colored solutions (5) Davis, Jeff C, Chemistry, 47,8 (October, 1974). can be obtained. For each of these solutions, the concentration (S) Davis, Jeff C, Chemistry, 48,11 (January, 1975). is adjusted so that no percentage transmittance (300-800 nm) (9) Davis, J«(TC., Chemistry, 49,18 (November, 1976). falls below 10%, and so that the major peaks of absorption ilO) BwfnftGalonW.,"lo5tMBCTtalMeUiodBof!3iemicalAnaiysis,"4tiie(i,Mc()raw-IBll, (400-700 nm) are clearly indicated, preferably with at least a New York, 1S76. Nbt necessarily for student use. This boot, references (IS) or (!9), minimum transmittance of 25%. These solutions, then, become or a current instrumental text could be usP*t alone. the student "unknowns." For student use, they should be labeled (11) KaUs.H., "The Limit of Detection of s Complete Analytical Procedure," (TWnlaior: Menzies. A, C), Hafner Publishing, New York, 1999. with their chemical name but without a concentration. (12) Macalady, Donald L., Chemistry, 48,87 (July-August 1975). (13) Meloan, Clifton E, and Kieet, Robert W.,"PwWemBend Eipsrimentsin Instrumental It is usually convenient, at this time, to prepare 100-200 ml Analysis," Charles E. Merrill Publishing, Columbus, OH, 196S. Either Uiisoj refer- of 1M stock solution for each compound used. In this way, so* ence (14) vrould be sufficient for background1- lotions are available for many of the standards and weighing can (H) Reilley, Charles N., and Sawyer, DonaSdT.,"Enperin»nts for Instrumental Methods," be kept to a minimum. All solutions should be stored in amber McGraw-Hill,^* York, 19SI. (15) Sandull, B. B. {Editor), "Colotimetric Determination of Ttaces of Metals," 3rd ed., bottles. Alternatively, students may prepare their own stock "Inter-Science Publishers: Chemica! Analysis," vol. HI, John Wiley and Sons, New solutions. York, 1959. Not necessarily for student use. The following compounds seem to work best as student (16) Sienko, Michael J., Plane, Hobert A., and Marcus, Stanley T., "Eiperimental Chem- "unknowns": nickel(H) choride hydrate, nickel(il) nitrate hy- istry," 6tii ed., McGraw-Hill, Nsw York, 1*76- drate, cobalt(II) chloride hydrate, cobaltdl} nitrate hydrate, (17) Skoog, Douglas A., and West, Donald M., "Fundamentals of Analytical Chemistry," copper(II) nitrate hydrate, copper(II) sulfate hydrate, chrom- End ed., Holt, Rinehart, and Winston, New Yoti, 1869. Not necessarily for student ium (III) nitrate hydrate, iron(III) chloride hydrate, iron(HI) use. nitrate hydrate, potassium permanganate and potassium (18) Skoog, Douglas A^ and West, Donald M., "Prindptea of InBtimnental Analysis," Holt, Biiwhart, and Winston, New York, 1971. Not necessarily for student use. chromate. The yellow solutions (iron chloride, iron nitrate, and (19) WniMd, H. H., Mettitt, L. L., and Dean, J. A., "Instrumental Methods of Analysis," potassium chromate) are more difficult to work with because 5th od, D. Van Nostrand, New York, S974. Not necessarily for student use, the color remains intense even at lower concentrations. Neither (201 Wine(ordner,J.I).(E*(ori,''TracBAnalysis:SpectroscopicMethodsfwtfeEleroBnts," manganese{ll) sulfate nor potassium dichromate are recom- "Intet-Seience Publishers: Chemical Analysis," Volume XLiV, John Wiley and Sons, Ne» York, 1S7S. Not necessarily for student uae. mended. Sample student data and a graph of absorbance versus (21) Diehl-Jones, Susan, J. CKEM. BDUC, «0.966 (1863). wavelength for determining the optimum wavelength ate given 11n the program described In the November, 1983 Issue of trie in the table and figure for Co(NO3)2-6H2O. JOURNAL OF CT«MGAI. EDUCATION, a three-week period was allotted ami was sufficient (21). 256 Journal of Chemical Education A New Method of Separating 210Pb from Ra-DEF for a Radioactive Equilibrium Experiment

C. M. Wai and J. M. Lo University of Idaho, Moscow, ID 83843

The decay of ai0Pb to 210Bi provides a good system to il- container walls and to control the forms of the ionic species lustrate secular equilibrium between a long-lived parent and in solution. After shaking the mixture for about a minute, the a short-lived daughter. system is allowed to stand still for the separation of two phases. If a centrifuge is used, phase separation can be achieved within a minute. The aqueous phase which contains g- 0.061M«V pr l.MMcV <, 5-SMcV pure 2J0Pbis ready for the secular equilibrium experiment. ». 22 y >. 2ioPo The time when two phases are separated is taken as the zero 6 6 139 d time for the experiment. 2l0 2l0 A general procedure of separating Pb from Bi for this To prepare a pure 21(|Pb source, an aliquot of the aqueous experiment is by means of a precipitation technique U). solution is taken from the via! and placed in a planchet. De- Carrier solutions made of bismuth nitrate and lead nitrate are pending on the activities of the Ra-DEF solution used, the generally used for the precipitation of either radioactive iso- aliquot size can vary from 20 nl to 200 ni. The radioactive so- 210 210 tope. Incomplete separation of Pb and Bi may result if lution is evaporated to dryness either at room temperature or pH of solution is not carefully controlled in the precipitation under a lamp. procedure. Another difficulty involved is to handle small quantities of precipitate and to make it into a uniform and Results and Discussion thin-iayer sample for counting. We have recently developed 2I0 210 ai0 a new method of separating Pb from Bi and Po by Theoretical Basis of the Separation Method means of solvent extraction of their diethyldithiocarbamate The proposed method of separating 210Pb from 210Bi and {C2H ) CS ~ complexes. This method involves a simple ex- 5 2 2 2!0Po is based on the difference in their complex formation traction procedure which allows complete separation of 210Pb constants with diethyldithiocarbamate. The extraction con- from Ra-DEF within several minutes. Since the radioisotopes stants of some metal-DDC complexes are given in the table. are separated in different solutions, they can be easily trans- The extraction constant of Pb(DDC)2 is much smaller than ferred and made into uniform thin samples by evaporation. 2+ that of Bi(DDC)3 or Po(DDC),,. Therefore, Pb can be sep- The experimental procedure and the basis of this separation 3+ 4+ method are described in this article. arated from Bi and Po in aqueous phase using a metal- DDC complex which has an extraction constant between those of Pb(DDC)2 and Bi(DDC)3. Experimental In this experiment, we chose to use BifDDCh to extract 210Bi and 210Po from the Ra-DEF solution. The concentration Reagents of Bi(DDC)a used in this experiment (about 10~a M) is much The proposed extraction procedure requires a diethyldi- greater than that of 210Bi present in the aqueous phase (about thiocarbamate (DDC) complex, Bi(DDC)g, which can be easily 4 X 10™11 M). Because of the large extraction constant for synthesized in the laboratory. The starting materials for Bi(DDC)a, virtually all 210Bi present in the aqueous phase synthesizing Bi(DDC)a are sodium diethyldithiocarbamate should be extracted into the organic phase by isotope ex- and a bismuth salt such as bismuth nitrate. The former can change with nonradioactive Bi in Bi(DDC). The extraction, be obtained from Baker or other major chemical companies. constant for Po{DDC)4 has been determined to be gTeater The synthetic procedure involves the reaction of Bi3+ ion with than that of BifDDOa (4). Therefore, in the extraction pro- 330 1+ DDC in aqueous solution followed by extraction of the metal cess, Po will replace Br to form Po(DDC)4 leaving es- complex with chloroform. After discarding the aqueous phase, sentially pure 210Pb behind in the aqueous phase. ethanol was added to the solution and the mixture was heated to 70°C to drive off chloroform. To avoid inhalation of Growth of^Bl from 2™Pb chloroform vapor, the whole experiment should be carried out in a hood. After evaporation, Bi{DDC)3 which is In general, the growth of a radioactive daughter product insoluble in ethanol, is recovered by filtration. The metal from a pure parent can be expressed by the following equation complex can be stored in a bottle for a prolonged period of (5): time, Radioactive Ra-DEF solution used in the experiment can be obtained from Amersham or New England Nuclear. (1)

2W Separation of Pb from Ra-DEF Extraction Constants " of Some Metal-Diethyldithiocarbamale About 0.1 to 1 jiCi of Ra-DEF is sufficient for a typical ra- Complexes dioactive equilibrium experiment. 21RPb is separated from a ai0 210 Extraction solution of Ra-DEF by extracting Bi and Po into a 0 Mela! Ion constant Reference chloroform solution containing Bi(DDC>3. The extraction can Complex be performed in a 5-ml polyethylene liquid-scintillation vial Pb(DDC)s 9.48 with a plastic cap. The Ra-DEF solution is introduced into 1 13.4 ml of a 2.4% HNO3 solution placed in a plastic vial. An equal Bi(DDC|a 13.6 (31 3 4+ Po(DDC), volume of CHC13 solution containing about 1.5 X 10~ M Po 14.1 Bi{DDC)g is then added to the radioactive solution. The acid * Extraction conslam •= 1/m log Kupoo^ J is defined as (M|0l3C)m]o.0' solution is used to prevent adsorption of radioactivities to the "*! [DDC-]m and m Is the charge of Ihe mutat Ions.

Volume 61 Number 3 March 1984 257 S

o.i 300 300 400 Time (hr)

Figure 2. Plot of (A* - A)/Ar. for Hie growth of *"tei.

2OO 400 000 800 If aiflPb and ai0Bi are in equilibrium in the Ra-DEF solution Tim* (hour) to start with, the activity of 210Bi found in the organic phase Figure 1. Growth of Bi from a pure "0Pb sample •and the decay of apure!!°Bi after Bi(DDC)3 extraction should represent A^. Another sample &. graphical illustration of the secular equilibrium is by plotting ln(A2eq ™ A^JMz611) versus tas shown in Figure 2. The slope of the line should be —X2. where A and X represent activity and decay constant and subscript 1 and 2 are for the parent and the daughter, re- This new method of separating Ra-DEF provides a simple spectively, If X<. is much greater than \i as in the case of a and fast procedure for studying the secular equilibrium be- 2I0 210 long-lived parent and a short-iived daughter, eqn. (1) can be tween Pb and Bi. It illustrates several important concepts simplified as such as solvent extraction, complex formation, and isotope exchange which are relevant to undergraduate laboratory

Az = Ai(l -e-**') (2) experiments in radiochemistry and in analytical chemistry.

2I0 The mathematical aspects of this experiment are important The beta activities from the decay of Bi can be measured for understanding the relations between parent and daughter by a Geiger-Miiller counter. A thin aluminum absorber (about in a radioactive decay series. 10 mg/cm2) should be placed between the sample and the G-M tube to remove weak beta emitted from 310Pb and to absorb the Po alpha particles. The growth of 2I0Bi from a pure 210Pb Literature Cited source obtained by this method is shown in Figure 1. The decay of a pure 2!0Bi source obtained from the same experiment is also shown in Figure 1. Jl) Chase, G, D.T rmd RabanowitK, J. L,, "Principles of Radioiaolope Methodology," 3rd ed., Burgp-Ge PubEJBhina Co., MinneppoJis, iH67, p. 179. Since at equilibrium Aj = A%, eqn. (2) can also be expressed (2) Shen, L. R, Veh, S. J.. and Lo, J. M..Anai Chum., £2,1882 (1980). (3) Yell, S. J., Lo. J. M.,and Shen. L. H.. Anal. Ckem., 52,528 U980). as (4) Wai.C. M.andLo, J. M.. Radiurhem. Radiaanal. ieii.,60,293 (1932]. i5) Friedlandet, G., Kennedy, J. W., Macias, E. S., and Miller, J. M., "Nuclear and Radio- .42 =- (3) chemistry." 3rd ed.. John Wiley & Sons, New York, 1981.

A Simple Method for Gleaning Mercury The usual method for the purification of mercury involves initial filtration, treatment with dilute nitric acid, and then distillation under reduced pressure.1 The facilities required are not always available in school laboratories and in many in- stances such highly purified mercury is not essential. Often, all that is required is a shiny mercury that does not stick to glass, and is suitable for filling manometers, etc. The following procedure is extremely simple, requires nothing more than a bottle and some sugar, and converts all those dirty old mercury samples into a bright, shiny, free-flowing liquid again. Procedure. Piace the sample of mercury to be purified (say 1-10 ml) inagiass (or plastic) jar with a tight-filting lid, add an equal volume of white sugar crystals (ordinary sucrose), and shake vigorously for several minutes. Pour the resulting mercury/sugar mixture into a large beaker or jar containing water, stir gently until the sugar has dissolved, decant the sugar solution and wash the mercury several times with water. The mercury can be dried either by rinsing several times with acetone, or by air-drying after removing the last droplets of water with a little absorbent paper (filter paper). We have been unable to find any reference to this method in the more common inorganic chemistry texts, but a similar procedure was reported iate in the last century,2 No explanation was offered as to why the method works, but presumably the major impurities (metal oxides, dust) are adsorbed onto the surface of the sucrose and in this finely dispersed form are easily floated off by the water upon dissolution of the sucrose. CAUTION: Carry out in a well ventilated area and carefully recover any spilt mercury droplets. Mercury vapor is highly poisonous and the effect is cumulative. 1 See for example, Vogei, A. I., "Quantitative Inorganic Analysis," 3rd ed., Longmans, 1961, p. 1056. 1 Dick, W. B,, "Encyclopedia of Practical Receipts and Processes," 5th ed., Dick & Fitzgerald Publishers, New York, 1892, p. 30fi. a 1874--1959. Benjamin Jenkins3 and Ian D. Jenkins School of Science, Griffith University Nathan, Queensland, 4111, Australia

258 Journal of Chemical Education Growth and Decay An Experiment Demonstrating Radioactivity Relationships and Chelate Solvent Extraction Separations

D. M. Downey, D. D. Farnsworth, and P. G. Lee West Virginia University, Morgantown, WV 26506

Many important techniques discussed in lecture material aqueous hydrogen ion concentration and the equilibrium frequently are not covered by laboratory experiments due to che!ate concentration in the organic layer, i.e., limitations in available laboratory time. Thus, experiments which demonstrate more than one concept are often more beneficial to the student than those which cover only one topic. We have attempted to include in the undergraduate Where K'ex is the extraction constant for the metal ion of radiochemistry laboratory course at West Virginia University larger charge value. experiments which teach both important radiochemistry It is useful to express eqn. (2) in logarithmic form: concepts and analytical chemistry techniques that are not + + covered in our forma! analytical laboratory courses. These log Kn = log [MRn]o + n log [H j - log |M" ] - n log JHA] (7) experiments include the determination of solubility product and solvent extraction partition coefficients, quantitative Rearrangement gives paper and thin-layer chromatography, metal separations by pH = ilog [MRn]0 - -\og |M»+] - log [HAL - - (8) ion exchange and solvent extraction, X-ray fluorescence and n n it activation analysis. Equation (8) may be used to calculate the threshold pH value One of the experiments, the separation of lead and bismuth which is the lowest value for complete extraction of the metal. by chelate solvent extraction, is of interest because of the It may be seen that the threshold pH is dependent on the simplicity which the use of radiotracers allows in its demon- concentrations of extracted metal chelate, residual (unex- stration. Chelate solvent extraction metal separations are tracted) metal ion, and unreacted chelating reagent in the usually discussed in the introductory analytical course but are organic layer. Thus, a threshold pH is calculated for a par- seldom demonstrated by experiment. Yet the separation of ticular meta! extraction based on the anticipated concentra- 2I2 lead and bismuth may be conveniently followed with Pb tions; then a pH value higher than the threshold pH is selected 212 and Bi which are readily obtained from natural thorium. and used in the extraction to allow for variable conditions. Furthermore, the parent-daughter relationship and the rel- 3+ 2 The separation of Bi from Pb * with dithizone (diphenyl- atively short half-lives of the tracers make possible the thiocarbazone) is a classic example of a chelate solvent ex- teaching of the laws of radioactivity in the same experi- traction separation (1). The published log K values for these ment. ex metals are 9.98 and 0.44, respectively (2) and these values allow the calculation of threshold pH values by eqn. (8) for the Theory separation conditions presented in the experiment below. If Metal ions may be extracted very effectively from aqueous a final aqueous metal concentration of 1 X 10~8 M is the cri- solutions by the formation of chelates with weak acids which terion for complete extraction (—100% extracted) from a so- are soluble in organic solvents. The genera! chelate extraction lution of initial metal concentration 2 X 10~5 with an initial process may be represented by organic phase of initial chelate concentration 8 X 10~5 M, then a 2+ + the threshold pH values are 2.46 for Bi + and 5.83 for Pb . M" + n(HR)o ** (MRn)o + raH+ (1) 3+ 2+ n+ Other values for the extraction of Bi and Pb have been for a metal ion, M , and che!ate, HR, with the subscript "o"calculated from eqn. (8) and are plotted in terms of the per- denoting the organic phase and no subscript denoting the centage of metal extracted versus pH in Figure 1. These curves aqueous phase. A nonthermodynamic equilibrium constant may be used to describe the process+ . That is [MR,,]O[H J» "ex ~ " (2) 100- Quantitative separation of metal M' from metal M" is defined as 80- L >100 (3) 5) 60- for the organic phase, and

Ml <0.OJ (4) [Ml x for the aqueous phase. The separation factor, a, is defined ui as 20- iM'R UM"] a = n ——- (5) [M*RB]O[M'] and must be greater than 10* for quantitative separation. It 2 3 * 5 6 7 may be seen from eqn. (2) that a is simply K'eJK"^ for two PH equally charged metal ions. For the separation of meial ions Figure 1. Effect of pH on the extraction of Bl3+ and Pbs+ with dlthizone In carbon s S which differ by one unit in charge value, a is dependent on the tetrachlorlde {initial concentrations: CH = 2 X 10~ M; Co = 8 X 1

Volume 61 Number 3 March 1984 259 are developed on the assumption that the dithizone concen- counts above background. However, the 212Bi will "grow" with tration is negligible in the aqueous phase and there are no time in the parent 212Pb according to the equation secondary complexing reagents present. Experimentally, it is found that optimum extraction for Bi3+ occurs at pH 3.2-3.4 and for Pb2+ at pH 8.6-9.2 (3). At pH 3.2, the a value for the dt Bi3+/Pb2+ separation calculated from eqn. (6) is well in excess 4 where the A values are the decay constants (0.693/ti/2) and JV of 10 and quantitative separation should be obtained. represents the number of atoms at a specific time after prep- Sever£d natural radioactive series were discovered early in aration of the radiochemically pure 2iaPb. Solution of eqn. (9) the history of nuclear science. One of these series has its origin for the number of mBi atoms at any decay time gives in a;!2Tb, which is 100% of natural thorium. The transforma- 232 tion of the radioactive Th to stable ^Pb proceeds through -JV< a variety of intermediate radioactive daughters by njeans of l>b six aipha and four beta decays. This group of radiormclides when there is no initial ai2Bi present and JVph is the initial is called the "4n" series since all the mass numbers are evenly number of ei2Pb atoms. Figure 2 illustrates the growth and divisible fay four. The overall decay scheme of the thorium (4n) decay of the radioactive materials. It may be seen that a series is shown below. maximum activity of the daughter is attained after 2.7 h and that radioactive equilibrium is attained after 3.8 h. After 3.8 h the 212Bi decays at the same rate as it is produced and the activity of the mixture decreases with the characteristic half-life of the parent ai2Pb.

Experimental

Materials A thorium cow should be prepared in the manner suggested by Morimoto and Kahn (4). Enough Th(OH)4 should be present to give 500 counts/s by G-M counting on the wire to provide sufficient activity for good counting statistics. The apparatus may be set up in a fume hood and left as a permanent source of the short-lived daughters. Two Geiger-Muller counters, each consisting of a G-M tube in a shielded lead castle and sealer/timer with aluminum absorbers (80 mg/ cm2), and a NaI(Tl) Scintillation Detector with 3.0 X 10"" 3 signal led into a Multichannel Analyzer (MCA) should be available" for j?~ particle counting and It may be seen that ^Rn is an intermediate product of the 7 spectra collection. A standard pH meter with glass electrode decay series. The radon is released as a gas from the solid and reference electrode is used for pH adjustment. parent material and provides a ready source of the short-lived Chemicals. Electrode calibration buffers

Washing the wire electrode with nitric acid provides a tracer 212 solution consisting of Pb (tm « 10.6 h), »«K {tin = 60.5 min) and 'm&T\ (tyz = 3.1 min) in radioactive equilibrium. These tracers are very convenient for use in the monitoring of the Bi/Pb separation discussed above. Furthermore they exhibit properties which make them useful for studying the laws of radioactivity. The 2l2Bi may be separated from the aisPb by the dithizone extraction procedure. The separated 2!2Bi may then be monitored with a Geiger-Muller detector to determine its half-life. More sl2Bi will begin to form in the separated 2l2Pb as it decays and this activity may be monitored to demonstrate the growth of daughter products in a radioactive parent.

The mPb emits up to 0.4 MeV 13™ in its decay whereas 212Bi Time, hrs. emits up to 2.2 MeV &~ particles. If an aluminum absorber of Figure 2. Aollvily variations with time. (A) decay of EISBI; (B) decay of 2fzPb; (C) 2 80-100 mg/cm thickness is placed between the separated growth and decay of I12Bi In initially pure z™Pb\ (D) total activity of Bie mixture 2!2Pb and the G-M tube, the detector will initially record no (B) + (C).

260 Journal of Chemical Education flasks, counting pianchets, heat lamp, and disposable CCU- Pipet 1 mL of this solution into a planchet (Planchet gloves. "C") and evaporate to dryness. Allow a 10-min decay of planchet "C" to reduce the activity of any coextracted 2OST1 Procedure (h/2 - 3.1 min) and count in the GM castle and NalfTl) de- ai2 Warning: The student should foe cautioned of the haz- tector as for pianchets "A" and "B". The half-life of Bi may ards of radioactive materials and volatile solvents. All be determined graphically from the data recorded by counting planchet "B" in successive 10-min intervals for up to 2 h. The work except counting should be carried out in fume hoods and 212 212 students should wear safety glasses, lab aprons, and disposable growth of Bi in Pb may be observed by counting planchet gioves at all times. Film badges, pocket dosimeters, and/or "C" for successive 10-min intervals in the second G-M castle survey meters should be used, and appropriate containers for with an aluminum absorber in place. radioactive waste disposal must be provided. The student should be aware of the particular hazard of accidentally in- Results gesting alpha-emitting radioisotopes and therefore pipetting Planchet "B" should contain 212Bi free from 212Pb con- by mouth must not be done. Radon gas is released upon tamination. Comparison of the beta activity cpm as deter- opening the thorium cow, and it must be kept in a properly mined by the G-M counting of pianchets "A" and "B" will vented fume hood to prevent inhalation. indicate the completeness of extraction and may be used to Transfer the wire electrode from the thorium cow to the indicate the students' laboratory technique. The students may small test tube, add 2 ml- of 2 M nitric acid, 0.5 mL of each be asked to comment on the "error" in the beta counts of planchet "A" due to the gamma activity of 212Pb. The radio- carrier solution, and heat to dissolve the radioactive daughter 212 products. Carefully transfer the cooled solution to a small chemical purity of the extracted Bi will be evident from the lack of a 0.24 MeV 212Pb peak in its gamma spectrum. The beaker, immerse the calibrated pH electrode and add several 2ia drops of concentrated ammonia to neutralize the acid. Care- completeness of the Pb extraction will be indicated by the comparison of the 0.24 MeV peak counts for ptanchets "A" fully adjust the pH to 3.0 using 1/10 ammonia and/or 1/10 212 212 nitric acid. Transfer the solution to a 10-mL volumetric flask and "C". Any residual Bi that is coextracted with the Pb and dilute to volume with distilled water. Pipet exactly 1.0 mL wiil be evident in the G-M count for planchet "C". The half- life of 2I2Bi may be determined from a plot of log activity of this solution into a counting planchet {pianchet "A") (Note Kl2 2!2 2) and evaporate to dryness with an infrared lamp. Planchet (cpm) versus decay time. The growth of Bi in Pb may be "A" serves a reference as it contains both aiaBi and B12Pb. demonstrated on the same graph by plotting the log beta ac- Count the planchet in the G-M castle with the aluminum tivity of ptanchet "C" versus time. absorber in place and determine the original counts per 212 minute {cpm) due to Bi (Note 3). Meanwhile, quantitatively Notes transfer the remainder of the aqueous solution to a separately 1) The diJution should not significantly change the solution pH. funnel with as small a volume of distilled water as possible 2) The extraction of Bi3+ proceeds slowly. Shake the separatory (Note 1) and extract twice with 4-mL portions of the dithizone funnel for 4-fl min per extraction. solution (Note 4). Quantitatively transfer the extract to a 3) The aluminum absorbers prevent the weak beta particles of 2iaPb second 10-mL volumetric flask and dilute to volume with from reaching the detector. CCL,. Pipet 1 mL of this solution into a planchet (Planchet 4) The student should calculate the net full energy peak counts as "B") and evaporate to dryness. Transfer planchet "A" to the explained by Bauer et al. (7). Nal(Ti) detector and record the cpm for the 0.24 MeV peak 2ia of Pb. Meanwhile count pianchet "B" in the G-M castle Literature Ctted under the same conditions as planchet "A" and record the 212Bi cpm. When the beta counts of aiaBi are recorded, U) Sanddl.R, B., "CatorimeEric Determination GfTraecs of MeEata," 2IKS ed., Intei-science, New York. 1956, pp. 388-402. transfer planchet "B" to the Nal(Tl) and record the gamma (2) fLuzjc&a. rl., and Stary, Jr, "Substoichionietry jrt Rwiinchemica! Anatysis." Pergamon, spectrum. Adjust the pH of the residual aqueous layer in the New York, 1968, p. VI. separatory funnel to 8.8-9.2 with a few drops of ammonia/ {3) Iwajjtachoff, <}., "lias DifJirzfln und seine Aifwettduug in der Micro und Spurenanalyae," Verlag Chemie, Weinheim, J958. ammonium chloride buffer. Extract twice with 4-ml portions (4) Murimoto. K M.,and Kahn. M. J., J. CHEM. Eixii:., 3fi, 296 (1959). of the dithizone solution. Quantitatively transfer the extract (6) Kvaie, E., and Sltarcstad, M., J. CHEM. EMJC, SI, 756 U974). (G> Broda. E.. aid Schonfdd.T.,•}. CKKM. iSDUC 5*, 577 flWIlh to a third 10-mL volumetric .fiask and dilute to volume with (7) Bauer, H. K. Christian, G. D., and O'Reiliey, J. E., "Jiistfuinpntal Analysis," Allyn and Bacun, Boston, 1975, pp. 676-577.

Double Balloons—Long Term Protection for Sensitive Materials In this laboratory we have been protecting basic solutions from carbon dioxide with an inert, dty nitrogen atmosphere. Normally one could use an ascarite tube (sodium hydroxide on asbestos) and change it periodicaiiy. We have discovered an excellent way to protect a solution with an inert atmosphere with a very inexpensive apparatus: one balloon positioned inside a second balloon. One balloon is forced inside of a second balloon with a pencil and the inner balloon is inflated with nitrogen. These "double balioons" are attached to tbe solution through a glass tube which protect* the solution with a positive nitrogen atmosphere. These "double balloons" will last for several weeks and when they

Volume 61 Number 3 March 1984 261 Phosphorus Determination by Derivative Activation Analysis: A Multifaceted Radiochemical Application

E. W. Kleppinger, E. H. Brubaker1, R. C, Young3, W. D. Ehmann, and S. W. Yates University of Kentucky, Lexington, KY 40506

Traditional neutron activation analysis (NAA) is a sensitive ders its determination by NAA in the presence of other beta technique which is applicable to about two-thirds of the ele- emitters impracticable without extensive chemical separa- ments. The remaining third, whose nuclear properties make tions. them difficult if not impossible to determine, include some Through the derivative activation technique, the desirable biologically essential and environmentally important ele- traits of an element such as vanadium can be employed to ments; conventional methods for many of these are both determine phosphorus. If phosphorus and vanadium are conjpiex and fraught with interferences. Hence the develop- chemically combined with a definite stoichiometry, deter- ment of derivative activation analysis (DAA), a method which mination of the indicator dement (vanadium) will give an extends the applicability of NAA to some of these elements, indirect measure of the amount of phosphorus present. Of is particularly significant. course, the chemical complex must be relatively stable and The determination of phosphorus is important in biology, easily separable from any excess of the indicator element. physiology, and environmental science; however, the tradi- While phosphorus has been determined through activation tional gravimetric and colorimetric methods are cumbersome of tungsten in tungstophosphoric acid (6), the more sensitive and lack the requisite sensitivity (J). We have adapted the technique we have appropriated involves the formation of a pAA determination of phosphorus (2) for use in a radio- stable phosphovanadomolybdate complex. This entity has a cfyemistry laboratory course, although this experiment would phosphorus-vanadium ratio of 1:2 under our experimental be, apropos in many other settings. The DAA method itseif is conditions and can be quantitatively extracted into methy! useful in teaching not only the principles of NAA, but also isobutyl ketone (MIBK) (2). problem-solving through the combination of several tech- Once the complex has been formed and isolated, the pro- niques. In this case, chemical, radiochemical, and instrumental cedure duplicates the NAA determination of vanadium. me^rfods are combined to accomplish what couid not readily Following irradiation of the sample, the 1.43-MeV gamma rays be achieved by any one of them alone. from the decay of 52V are instrumen tally segregated and counted. If absolute activity (A) can be ascertained, the amount of Jn thermal NAA (3, 4), a stable nuclide captures a neutron vanadium present can be determined from the activation to forni a heavier isotope, which typically decays by the analysis equation (3).

emission of a beta particle and one or more gamma rays. Since !ii the gamma-ray energy is characteristic of the particular ra- A = nfa(\ — e-*

262 Journal of Chemical Education Sample Data

Specific Activity Student Count Rate (cpro) Standard Samples Results Group Standard Sampies Background (cpm/mg P) (cpm/mg PF) <%P>

2 52? ± 8a 519 ±8 368 ±7 238 ± 19 13.1 ±0.9 4.63 ± 0.44 495 ±8 11.0 ±0.9 3.89 ± 0.41 507 ±8 12,0 ± 0.9 4.24 ± 0.43 4 193 ±5 205 ±5 119 ±5 138 ± 12 6.65 ± 0,55 4.82 ± 0.58 207 ±5 6.80 ± 0.55 4.93 ± 0.58 211 ±5 7.11 ±0.55 5.15 ±0.60

> Statistical uncertainties only are presented.

Equipment, The chemical procedures are carried out with Discussion readily available laboratory accouterments. Volumetric In any experiment involving radioactivity, the question of glassware, separatory funnels, irradiation vials, and an ana- safety invariably wiU arise. Derivative activation analysis is lytical balance are accessible for genera! use. particularly appropriate for a teaching laboratory in this re- Neutron source. The irradiation vials are lowered into ports gard, Ail chemical procedures are carried out before any ra- 252 5 4 cm from a Cf source where the flux density is about 2 X dioactivity is induced. When activity is handled, it is in a fi 2 ] 10 neutrons cm* s~ . sealed vial, and the short half-life of 62 V and relatively small Instrumentation. Figure 1 shows a block diagram of the amount of vanadium present keep the total activity quite low. instrumentation used. The irradiation vials fit snugly into the In addition, no radioactive waste is generated; within a half- well of the 3.8 cm X 3.8 cm NaI(Tl) crystal. The single channel hour of removal from the neutron source, less than 1% of the analyzer is set by leaving the window wide open and raising the discriminator until no appreciable count rate is observed with a 13?Cs source (£, = 0.662 MeV) (6) near the crystal. Procedure. Standard (KH-2PO4) and sample (plant food) solutions are accurately prepared with distilled, deionized water to be about 20 ppm phosphorus. Analysis is performed • "*" " Vial T'F[lt' on 25-mL aliquots of standard and sample. 3.8 K 3.B cm The phosphovanadomolybdate complex is formed directly I Crys'al 5149 in separatory funnels, as follows: To each aliquot of phos- Ph'cio - phorus solution, 5 mL of concentrated nitric acid, 5 mL of Suppiy pter vanadate solution, and 10 mL of molybdate solution are • 1000V Hi added. Pipets are used to measure all volumes. Each separa- Tube tory funnel is shaken well and allowed to equilibrate for 5 min. The appearance of a bright yellow color in solution indicates Figure 1. Block diagram of gamma-ray detector and electronics. the formation of the complex.

A IG-mL aliquot of MIBK is pipeted into each funnel. The organic and aqueous layers are intimately mixed by shaking at 30-s intervals for 5 min. The layers are then allowed to .CALCULATIONS. separate undisturbed for 30 min. Half of each organic layer {5 mL) is transferred to a labelled polyethylene irradiation vial. The vials are sealed with epoxy or "heat sealed." STANDARD PROCEDURE SAMPLE Each specimen is irradiated for 10 min in the 232Cf source % phosphorus and counted for 8 min in the Nal(Tl) well crystal. A 1-min % phosphorus tn planl fbod waiting period is allocated between irradiation and counting in KHEP04 1 nominal 1 to allow for transfer of the vial from the neutron facility to the gamma-ray detector. weight phosphorus Prepare Standard weight plant food m ) L and plant food in I L of sofuiion solutions. of solution Results

Representative data are presented in the table. The sig- weight phosphorus weight plant food nal-to-background ratio is limited both by the efficiency of Totie 25 mL aliQuats in 25 mL in 25 mL of each. the relatively small well crystal and by the amount of complex of solution Of solution soluble in 5 mL of MIBK. The great variation in counting rate originates from the use of various counting conditions and Form complex; shielding arrangements around the detector. weight phosphorus weight plait food extract and transfer in 5 mL MISK The calculations, although straightforward, involve several in 5 mL MI9K to viat. steps. There are many ways to obtain the results from the data; presumably the most instructive is to carry out the cal- ; culations in the same logical order in which the experiment activity Irradiate and specific ccliviiy was performed (Fig. 2). This method serves to reinforce the (cpm/mg PI count. (cpm/mg plant lood) logic and purpose of the experimental procedure, Results calculated from student data are presented in Figure 3. All students worked in groups of two or three and % phosphorus in plant food analyzed the same plant food. Each result is a weighted av- cpm/mg PF erage of three sample determinations. The error quoted is X 100 % cpm/mg P obtained through propagation of a one-sigma statistical uncertainty, associated with the counting of decay events. Figure 2. Logical sequence of calctitatlona! steps fot determining %P.

Volume 61 Number 3 March 1984 263 * 1 ! ! 1 iment is viable with more available neutron facilities. For example, plutonium-beryllium sources provide up to 1.4 X 107 neutrons s~' Ci~! (3), which is more than ample for this ex- 252 5.0 — h periment; and smail Cf sources are becoming increasingly more commonplace. Less potent sources could be used in conjunction with more concentrated samples and a larger o 1 volume of MIBK in order to yield the requisite level of ac- 4.5 tivity. I CL 11 In nitric acid medium, there are virtually no ionic interferences to the determination of phosphorus. Samples of 4.0 water, coal, biological tissue, and rock and mineral matter have been assayed successfully by DAA (2). Solid samples must first be dissolved, and all samples must be preconcentrated 1 1 1 1 1 or diluted, if the phosphorus concentration is not between 1 ng/mL and ~30 jUg/mL. The upper limit is determined by the solubility of the phosphovanadomolybdate complex in MIBK, Group Number and the lower limit by the available neutron flux density (1 X 10« n cm-2 s~J for 1 ng/mL) (2). Figure 3. Student results lor %P in Ortho House Plant Food 5-10-5. The flashed iine depicts 10% Ps05 (4.4% P), as quoted on the piant food label and pre- With its wide options for sample type, neutron source, and sumably represents a lower limit. counting instrumentation, DAA of phosphorus emerges as a versatile analytical method in addition to being a very useful teaching tool. initial activity is present and the organic solutions may be disposed of through normal procedures. Literature Cited This experiment has two features which particularly rec- (1| KuliJraff, S. M, Sandell, E. B., Median, B. J., and Bruckenetein, Stanley, "Quaniative ommend it as a teaching tool. First, it can be completed in one Chemicai Analysis," 4th od., Macmillm. Lotulon, L9«», pp. 1125-1129. (2) Vouifg, Robert Cornwell, •''Derivative Activation Afialysie Applied to (ire Determination laboratory period. All students performing the experiment of P, Ni, and Tl," Ph -D. Dissertation, University of Kentucky, 1979, carried out their laboratory work comfortably in 3-4 h. Sec- 13» DeSoete, D.T Gijbclo, R., and Hoste, Jr, "Neutron Activation Analysts." Chemicftt Analysis ond, this determination yields good results without undue Monographs, Vol. 34. Wiley-Inlersdeuoe, NRW York, Ifl72. meticulousness. Student data attest the fact that the method (4) Ehmann, W. D.. "Non-destructive. Tftchniques in Activation Analysis," Topics in Current works well. Chemistj-v.Bii. KHf.l.Sprbiger-VMlag.Borlbi, 1970, pp. 49-91, (5) Lederei, 0. M, and Shirfey, V. S., "Table o£ Isotopes," 7th od., John Wiley & Sono, Inc., While activation analysis with a nuclear reactor as the New Vork. IOT8. source of neutrons has been widely exploited (7), this exper- (6) Alien, H. F,, and Hahn, U.B., Erw. Sri. Tech., 3, a44 (1969). 17) Kenyan, Krishnaswamy, J, CHBM. EDUC, 55.203 {1976}.

HPLC Analysis of Chlorophyll a, Chlorophyll b, and ^-Carotene in Collard Greens A Project for a Problem-Oriented Laboratory Course

Augustine Silveira, Jr., Jerry A. Koehler, Edward F. Beadel, Jr., and Pearle A. Monroe State Universfty of New York, College at Oswego, Oswego, NY 13126

The theory and application of high performance liquid Experimental chromatography should be an integral part of college chemistry curricula since many students will be utilizing this Instrumentation technique in their profession. A popular experiment (J, 2) in The instrument used was a Varian 5020 liquid chromato- undergraduate organic laboratories is the separation of a ca- graph equipped with a Model UV-10 variable wavelength rotenoid, such as ^-carotene, from the chlorophylls in vege- detector and a Model 9171-02 duaj-pen, strip-chart recorder. tables (e.g., collard greens, spinach, etc.) using column or thin The 4-mm X 30-cm prepacked analytical column for this layer chromatography (TLC). We have expanded this tradi- separation was a MicroPak Si-5(Silica). A 4-mm X 30-cm tional experiment fay utilizing high performance liquid chro- bonded reverse-phase column (monomeric octadecylsilane) matography (HPLC) to separate and quantitate ^-carotene, MicroPak MCH-10 also was used. For a comprehensive dis- chlorophyll a, and chlorophyll b originating from collard cussion of reverse-phase chromatography, see reference (6). greens. This experiment clearly illustrates to the student the Each of these analytical columns was preceded by its appro- versatility of HPLC as a powerful analytical technique. A priate 4.6-mm X 3-cm pre-column. The mobile phase was a project undertaken by SUNY Oswego students who have nonlinear, step-an

264 Journal of Chemical Education Sample Preparation Average HPLC Student Results ol /^-Carotene, Chlorophyll a, and Separatory Funnel Extraction Method. Crush approximately 15 Chlorophyll b from Coltard Greens g of fresh or frozen eollard greens in 50 ml niethanol with a mortar and Pigment Occurrence8 pestle. This is to remove as much water from the plant ceils as possible. Decant and discard the methanol solution and press the vegetable ^-Carotene 47 X 1IT6 g as tree of solvent as possible. Regrind the coiiard greens with 3 5 ml Chlorophyll a 1.6 X 1{T6g methanol and 25 ml isooctane. Filter the mixture through a glass Chlorophyll b 1.2 X 10~eg funnel plugged with absorbent cotton into a 125-ml separatory funnel. Again, regrind the vegetable with I5ml methanol and 25 ml isooctane. " Values ate expressed as per grem trash wetght of eollard greens. Siandards wme Filter as previously and place in the separatory funnel. purchased from Sigma Chemical Company, P.O. Box 14508. St. Louts, MO 6317S. Discard the lower inetianol phase and add 30 mi water to the separatory funnel and shake gently. If an emulsion appears, add sodium chloride. Repeat as previously with another 30 ml water. Plate the isooctane solution into a 125-ml Erlenmeyer flask, and The selectivity (a) class value for chlorophyll a and b was dry by adding 1-2 g anhydrous sodium sulfate. Decant the liquid into 1.4, and the resolution was 1.1; this indicates that if one wished a sample bottle with a screw lop. Fill to the top with additional igo- to collect the samples, one would obtain approximately 99.2% octane as needed. This minimises contact of the sample with oxygen. of each component. The average HPLC student results, ex- Strong light and oxygen hasten the decomposition of components. pressed as per gram fresh weight of eollard greens for ^-car- To exclude light, the sample bottle is wrapped tightly with aluminum otene, chlorophyll a, and chlorophyll b are summarized in the foil. Save the sample for HPLC analysis. table. The other, unidentified compounds appearing in the 2 SEP-PAK" Extraction Procedure (7). Add 10 ml 2-propanol to chromatogram are typically pheophytins (chlorophyll which 5-10 g of coiiard greens and stir with a mortar and pestle for 1 min. has lost its magnesium), chloropnyilides (chlorophyll which The 2-propanol serves to eliminate the water from the disrupted cells has lost its long-chain alcohol, either phytol or farnesol), (i.e., same as methanol). Press tiie vegetabie as free of solvent as pheophorbides (chlorophyHides which have lost their mag- possible and decant the mixture. nesium), or pheophytins which have lost their phytol Extract the pigments by adding 5-10 ml isooctane and stirring. moiety. Decant the green colored mixture. Evaporate the liquid almost to dryness using a steaffl bath. Add 2-5 ml isooctane through the silica The literature is replete with time-consuming separations SEP-PAK™ with a I.uer-type syringe. Immediately dissolve the ex- utilizing column or thin layer ehromatography {8-11). Evans tracted residue in 3 m! isooctane and pump it onto the premoistened et a!. (12) have separated two chlorophyll derivatives with ailica SEP-PAK cartridge with the Luer-type syringe. Flush 3 ml high-pressure liquid ehromatography and Kskins et al. (13) isooctane through the cartridge and discard the eluate. With 5 ml 2-propanol elute the yellow and green bands, collecting only the col- have described a preparative HPLC procedure too lengthy for ored bands. Place this in a screw-top sample bottle, fill to the top with routine analysis, Shoaf (14) has separated chlorophyll a and 2-propanol and cover the vial with aluminum foil. b from aquatic algae utilizing dimethyl sutfoxide as the extracting solvent and water-methanol as the HPLC mobile Results and Discussion phase and Braumann and Grimme (15) have done a single- step separation of photosynthetic pigments with HPLC. The A typical chromatogram obtained by students showing the chromatographic separation of /i-carotene, chlorophyll a, and separation of j5-carotene from chlorophyll a and chlorophyll chlorophyll b by TLC and open-column methods is time- b ia shown in the figure. The entire HPLC analysis can be consuming and causes pigment decomposition by exposing accomplished in about 25 min. Interestingly, both the silica these labile compounds to oxygen, h'ght, solvents, and adsor- and the oetadecysilane column gave comparable class results, bents for relatively long periods of time. with the more polar compounds being eluted last Therefore, in the octadecylsilane run, one is actually observing a form of The project we have described demonstrates to the student "reverse-reverse phase" (i.e., normal) ehromatography. The that high performance liquid ehromatography is useful for HPLC class results from either the longer separatory funnel rapid quantitative identification and analysis of such com- extraction method or the shorter SEP-PAK™ preparative pounds as plant pigments. Because the separation is rapid and procedure also gave comparable HPLC results. requires only a few, inexpensive standards, it can be integrated easily into existing laboratory curricula.

1 Information on SEP-PAK™ cartridges may be obtained from Waters Acknowledgment Associates, 34 Maple Street, Milford, MA 01757. A. Silveira, Jr. gratefully acknowledges the National Science Foundation for support in the purchase of the Varian HPLC 5020 High Performance Liquid Chromatograph and the State University of New York Research Foundation for Improve- UJ O ment of Undergraduate Instruction for its continued support of project-oriented laboratories. < ChlA o Literature Cited to (1} Pavia.D. 1,., Latnpni&n, G. M., and Kris. G. S., "tntroduciion tn Organic Laboratory CD Techniques, 2nde&, W. B. Saundeis Co., Philadelphia, PA, 1982, pp. 'iSS-HS. < (2) Mwire, J. A., Dakytnple, D. l_,and Rodig.O. R., "Experimental MetJinds in Organic S~ Carotene Chemistry." 3rd ed., W. B. Saundeis Co, Philadelphia, PA, 1982, pp. 83-89. LU v. (3) SilvBira.A.,Jr.,J.CHEM.EmJC., 55,57 (1978). (4) SiIve!ra.A.IJr.,asdSatra,S. K..J. Org. CAem.,44,873 0979). ChiB (5) Silvcini, A., Jr., Brelhprlck, H. D., and Negishi, B., Z. CHEM. EtillC S6,560 (1979). (6) Colin, H., and Game!™, G.,J.e/jr<™ieio,Br., 141,288 (]977). (7) McKone.T. H.,J.CH1!M. KDUC, 56,676 (1979). _J _* (8) Jeffrey, 8. W, Bimhim. Biophys, Acta, 162,27i (1968). (9) Jones, ].T>., Ballet, I,. S.,Gibb8. E., and While, H. C..J. Chmtrwtogr., 71), 87 (19721. LU (10) Daley, R. J.. Gray, C. B. J., and Brown, S. H..J. Chramatogr., 76,175 (1973). f 11) Shnof, W. T., and Limn,B. W., J. Re*. U.S. Gml. Sum., a, 263 (1977). (12) Evane, N, Games, 0. E, Jackaun, A. H., and Mallin, S. A., J. Chromatcgr., 115,326 TIME (1975). (13) EsWns, K.,Schoifie!d, C. R.. and Button, H. J., J. Cliromatngr., 135,217 (1977). Chromatograpf! ol ^-carotene, chlorophyll a (Chl^), and chlorophyll b (Cht,,) from (14) Hhnaf, W. T., J. CAromntair., 152, 247 (1978). 1 collard yeans by the SEP-PAK " method. (15) Brarnnsnn,T.,andlJrimine.L.H.,J.C/iran)Otoi'f.r 170.364(1979).

Volume 61 Number 3 March 1984 265 Southeast edited by NANCY LEMASTER D. W. Daniel Nigh School Central, SC 29630 ADVANCED PLACEMENT SEMINARS April 3,1994 University of Kentucky, Student Center Annex, Lexington, KY 40506. For further information, contact: Timothy R. Burcham (606| 257-1608. April 10,1984 Tennossee Technological University, University Center, Coofcesville, TN 38501. For further information, contact: James C. Perry, (615) S38-3888. For the State of Ftorida, Hie list of AP seminars may be obtained. For further Information, see the February 1984 Issue of TUB JOURNAL, May 10-12, 1984 37TH ACS FLORIDA SECTION ANNUAL MEETING at Florida Southern Colfege, Lakeland, FL. For further information, see the February 19S4 Issue of ma JOURNAL.

Northeast edited by WALLACE J. GLEEKMAN Brookiine High School Brookline, MA 02146 March 26-28, 1984 NEW YORK ACADEMY OF SCIENCES CONFERENCE ON MACRO- MOLECULES AS DRUGS AND AS CARRIERS FOR BIOLOGICALLY Northcentral edited by ACTIVE MATERIALS to be held at Ihe Roosevelt Hotel, New York, ROBERT SUITS NY, D. H, Hickman High School For further information, see the February 1984 issue of THIS JOURNAL. Columbia, MO 65301 April 5-8, 1984 April 6-7, 1984 32ND ANNUAL CONVENTION OF THE NATIONAL SCIENCE The 63«o 2YC3 CONFERENCE at the St. Louis Community College TEACHERS ASSOCIATION (NSTA) will be held at the Sheraton- at Florissant Valley, 3400 ParshaH Road, SI. Louis, MO 63135, tn BOSIQR and the John B. Hynes Auditorium In Boston, MA. conjunction with the 187th ACS National Meeting April 8-13, For further Information, see the February 1984 Issue of THIS JOURNAL. 1984. For further information, see the February 1984 issue of THIS JOURNAL. April 5, 1984 ALL DAY CONFERENCE ON ACID RAIN sponored by Northeastern April 8-13,1984 Section, American Chemical Society to be held at the Sheraton- 187TH ACS NATIONAL MEETING, St Louis, MO. Lexington Hotel, Lexington, MA. For further information, see ttie February 1984 Issue of THIS JOUHNAL. Keynote speaker: Dr. Michael Oppenhelmer, environmental Defense Fund, New York, NY. April 9, 1984 For further information, contact: Marlon Ryan, Polaroid Corporation, 750 "HIGH SCHOOL DAY" at the ACS National Meeting, St. Louis, MO. Main Street—IR.Carobrlriga, MA 02139, (617)577-3585. For further information, see Die February 1984 issue of THIS JOURNAL. April 7,1984 May 23-25,1984 A VERY A. ASHDOWN HIGH SCHOOL CHEMISTRY EXAMINATION JOINT GREAT LAKES CENTRAL REGIONAL MEETING, Kalamazoo, CONTEST sponsored by the Northeastern Section, American Mt. Chemical Society to be held at Simmons College, 300 The Fenway, For further information, contact: L. E. Mines, Upjohn Co., 301 Henrietta Boston, MA. Street. Kalamazoo. Ml 49001, (616) 385-781B. For further Information, contact: Ivan VanderWorkeen, Chemistry Dept., Westwoorj Hfgh School, Westwood, MA 02090, (617) 32B-750Q. May 21-23, 1984 18TH MIDDLE ATLANTIC REGIONAL MEETING, New Jersey Institute of Technology and Rutgers University, Newark, NJ. For further Information, contact: G. E. Heinze, Jartsen Pharmaceutica inc., 501 George St., New Brunswick, NJ 08903, (2011 524-9575. May 31-June 2, 1984 11114 CONFERENCE OF COLLEGE CHEMISTRY CANADA to be held at John Abbott College, Montreal, Quebec. Theme: Life in Chemfstry == Chemistry in Life Northwest edited by For further information contact: Shahld Jalil, John Abbott College, P.O. DOUGMAOCIT Box 2000, Ste. Anna de Bellevue, P. O, H9X 3L9. Sumner High School Sumner, WA 98390 June 10-14, 1984 14TH NORTHEAST REGIONAL MEETING, Fairflefd University, Fair- June 13-15, 1984 field, CT. 39th NORTHWEST REGIONAL MEETING OF THE AMERICAN For further information, contact: D. L. Swanson, American Cyanamid CHEMICAL SOCIETY at the University of Idaho, Moscow, ID. Co., Chemical Research Division, 1937 West Main Street, Stamford, CT For further information, contact: Dr. Steve Brown Washington State Uni- 06904,(203)348-7331, versity, Pullman, WA 99164.

266 Journal of Chemical Education Southwest edited by More on Chemical Stereoviews ERIC STREITBERGER To the Editor: University of Callfornla-FuHerton Fuilerton, CA 96231 Since writing the note on the construction of a resource file for chemical stereoviews,1 1 have come across a number of TEACHER WORKSHOPS sponsored by the Colorado additional references dealing with the history of chemical ACS Section, Regis College, Room 312 Science Bfdg., stereoviews as well as several new sources of potentially useful Denver, CO 80221. 8:00 a.m.-5:00 p.m. stereoviewa, both of which may be of interest to the readers April 7,1984 of THIS JOURNAL. Dr. Ivan Bernal has called my attention to Descriptive Chemistry of Metals an extremely interesting collection of stereoscopic drawings, May 5,1984 edited by von Laue and Mises, and published as two separate Descriptive Chemistry of Non-Metals volumes by Springer Verlag in 1926 and 1936.2 These volumes For further Information, contact Evelyn Bank Chairman of the Cotorado contain a tola! of 48 hand-drawn stereoviews illustrating the ACS Section, Westminster, CO 80030, (303) 428-9541 Ext. 343 or (303) 14 Bravais lattices and the structures of 34 elements and 424-3162. simple inorganic compounds, ranging from NaCl to perovsk- 3 WEDNESDAY AFTERNOON LECTURES being held at ite. The 1921 crystallography text by Groth also contains a collection of stereoviewa, though these are stereophotographs California Institute of Technology, 3rd floor, Baxter of actual physical models rather than line drawings. Hall, Pasadena, CA. These lectures begin at 3:30 p.m. and are free for secondary school The back cover of the April, 1929 issue of the JOURNAL OP students and teachers. They are as follows: CHEMICAL EDUCATION carries an advertisement for Fisher Aprlt 4,1964 Scientific, complete with a photograph, of a "Camerascope" The Crack: the Most Expensive "Nothing" for "visual instruction in X-ray crystallography." This device Speaker: Di". W. T. Knauss, Professor of Aeronautics a Applied Me- sold for the then rather expensive price of $18.00 and consisted 4 chanics of a small folding stereoscope and 37 stereoviews. From the May 2,1984 description it is apparent that it was essentially an American The Atomic Nucleus: Quantum Physics on a Grand Scale version of the Bragg set mentioned in my original note. Speaker: Dr. S. C. Koonln, Professor of Theoretical Physics. For turther information on the above lectures, contact Lee F. Browne, or As for sources of stereoviews, the first volume of the series Phyllis Brewster, California institute ot Technology, Pasadena, CA "Molecular Structures and Dimensions," published by the 6 91125,(213)356-6624. International Union of Crystallography, contains close to 920 computer-drawn stereoviews of organic compounds, organometailic JT-complexes, charge-transfer complexes, ciathrates, carboranes, and traditional metal complexes of organic ligands. Regrettably, a similar source of stereoviews for non- molecular solids is apparently still lacking.

LETTER; William B. Jensen University ot Wisconsin Madison, Wl 53706 The Error in In x To the Editor: 1 Jensen, W. B., j. CHEM. EDUC, 59, 385 (1982). I found Leonard Nash's article on the "Ice Point and Triple 2 von Laue, M., and Mises, R. {Editors), "Stereoscopic Drawings of Point" in the December 1981 issue quite interesting, partic- Crystal Structures," Vols. 1 and 2, Springer, Berlin, 1926 and 1936. 3 ularly his pointing out that a four digit logarithm can yield a Groin, P., "Elemente der Physikalischen und Chemischen Krisial- six digit antilogarithm. lographie," Oldenbourg, Berlin, 1921. 4 J. Crew. EDUC., 6,4 (1929). Although his demonstration was moat convincing, I should 5 Kennard, O., et ai. {Editors), "Molecular Structures and Dimen- like to suggest an alternative derivation of his result. If we use sions," Vol. A1, international Union of Crystallography, 1972. the notation of calculus for finite changes (errors), then we may write than an error in x, d(x), causes, in the logarithm of x, In x, an error d(ln x) given by The Supporting, Rather than Initiating, Rote of Science In Technology Thusd(x) = x d(hix), the errorn i To x the Editor: isx itself multiplied4 by the errorn i the logarithm. In his editorial in the May, 1982 issue of THIS JOURNAL In one of Nash's cases, where Inf'Th xe 7 Publi -c Attitud -8.23e0 Towar Xd Science") 10~, J. J . =Lagowski —0.0008230, fi we assume an error ocorrectlf ±y 1lament ni s the prioritie thes o flas thet America digint public for the quoted, then d(ln x) = 2 X suppor10~.t o fNo sciencwe an xd technolog itselfiys wit hmanifestl tax revenuesy, neaas inr- 1 (i.e., 0.9991...), thus dicated by the most recent annual report of the National Science Board, Science Indicators 1980. He comments that d(x) * (1)(2 x 10-') "It should be more than slightly disturbing to the scientific community that the general public perceives the acquisition or the resulting x is determined too fwithi newn knowledge—th 2 ni e fundamenta the lsevent basish of modern tech- figure. nology—to be so lacking in merit as to place it among the Note that the above-relationship indicateslowes that otn th eth Hset of area erros tro be supported." While the public's increases with increasing x and that Jacthek of appreciatio inversen procesfor the sbenefit ofs to modern society of obtaining hi x, given x, can leadfundamenta toquit el researc largeh is errorindeeds caus fi e for x concern is, Lagowski' verys small. justification for the acquisition of new knowledge as "the fundamental basis of modern technology" is ill-suited to his Oliver G. Ludwtg purpose. Historians of science and technology have in recent Villanova University years devoted much effort towards the elucidation of the in- VMtanova, PA 19085

Volume 61 Number 3 March 1984 267 fraction between science and technology, and a consensus Soiled Chemistry has emerged that technological innovation most often evolves To the Editor: from prior technology, and that when pure science does play a role, its relation to the technological developments are sel- There are significant agronomic errors in the experiment dom those of cause and effect. In a carefu! study, for example, entitled, "Soil Analysis for High School Chemistry Students," of 84 successful British technological innovations of 1966/67, by Mary A, Eisenmann, published in J. CHEM. EDUC, 57,897 F. R. Jevons found the role of science to he a supporting, rather (1980). The Discussion section has several significant errors: than an initiating, one and that in no single case was an in- 1) The fertilizer analysis 15-5-10 means 15% N, 5% PaO5, and novation induced by a scientific discovery.1 10% K2O, not 5% P and 10% K as stated in the article. The state fertilizer registration laws are 20-30 years behind the Tf we choose, as many of us do, to justify the pursuit of times. 2) In soil that is too alkaline (basic) (pH > 8), the mi- knowledge primarily by consequent technological innovations, cronutrients zinc, copper, iron, and manganese are tied up as then the importance of pure research will be diminished if, as insoluble phosphates and the phosphate ions (HPO/") are seems likely, the justification ia rendered invalid. It is im- unavailable because of the formation of insoluble calcium and portant for modern scientists, of whom chemists form a large magnesium phosphates. 3) In acidic soils (pH < 5) the mi- percentage, to seek societal support for the pursuit of new cronutrients {trace elements) manganese and iron become too knowledge as an integral part of the cultural attainments of available and may reach toxic levels. Aluminum becomes a mankind, a part moreover which encourages us to appreciate, significant problem also. The ideal soil pH is 6.5, the pH of utilize, and live in harmony with, the world around us. maximum major and secondary nutrient availability and proper mieronutrient availability. Meivyn C. Usselman A professional soil testing laboratory tests for the primary Univelrslty of Western Ontario and secondary plant nutrients—N as NO3" by specific ion London, Ontario Canada N6A 5B7 electrode, P colorimetrically as the blue phosphomolybdate complex, and K, Ca, and Mg by atomic absorption-emission spectroscopy. The mieronutrients ate also determined by A A.

1 A soil lab does not test for HCC>3~. pH is measured with a pH Jevons, F. R., Technology & Culture, 17,729(1976). meter. Na-Churs Plant Food Company analyzes approximately 130,000 soil sample a year for its fertilizer cus- Liability insurance tomers. To the Editor. I wili be happy to answer any questions about soil testing, agronomic recommendations, fertilizer manufacture, etc. A contribution to the Safety Column last November by N. T. and Marilyn C. Kurnath1 has pointed out the increasing numbers of law suits charging negligence on the part of labo- Walter C. Crause ratory teachers. This has raised questions about liability in- Director, Product Research surance for the financial protection of teachers and prompts Na-Churs Plant Food Company 421 Leader St. us to call special attention to the ACS Professional Liability Marion, OH 43302 Insurance Plan, just in case our readers failed to note the paid advertisement on page A344 of that same issue. An Alternative Proof Reductions in rates have made this coverage a genuine To The Editor: bargain in the opinion of your Column Editor. For peace of mind and the protection of your solvency we recommend Carl W, David's article, "Why is an LCAO-MO Not Nee- writing for full information. Address inquiries to the American easarily an Eigenfunction," which appeared in the April 1982 12 Professional Agency, Inc., 95 Broadway, Amityville, NY 11701. JOURNAL provided one demonstration that ^ttiai lsa+ lsb (The plan also includes coverage for industrial chemists, and is not an eigenfunction of the one-electron Hamiltonian H. an alternative plan is available for consultants.) I would like to suggest a much simpler and perhaps more interesting proof. Malcolm M. Renfew Consider

University of Idaho ff&iia] = HfiV2m)V2 _ Zeyre _ Ze v,-b](!sa + iSh> Moscow, ID 83843 But lsa is an eigenfunction of the first two terms in H, and \#h is an eigenfunction of the first plus the last term in H. In each 1 Kurnath, N, T. and Kurnath, Marilyn C, J. CHEM. EDUC., 58, A329 case, the eigenvalue is simply the hydrogen-like atom ground (1981). state energy Euv = -{13.6 eV)Z2. Therefore

Crib Cards for Tests To the Editor: and I would like to note that Whitmer'a suggested use of a 3 X 5 "crib card" on tests [J. CHEM. EDUC., 60,85 (1983)] is not limited to physical chemistry. I have successfully used the same idea for several years in my sophomore organic chemistry course and I concur with Whitmer's comment that preparing It is impossible to factor the last two terms to yield simp the card is an excellent focus for study. I have had students multiplied by a constant. Therefore, ^jai is not an eigen- complain that by the time they have figured out what they are function of H. going to put on the card they no longer need the card. I rec- This proof exploits essential properties of the Hamiltonian ommend its use by instructors interested in testing the use of H as weD as of the AO's lsB and lsb- and offsets any need to facts without testing the memorization of those facts. consider specific functional details.

John Henderson Frank O. Ellison Jackson Community College University of Pittsburgh Jackson, Ml 49201 Pittsburgh, PA 15260

268 Journal of Chemical Education BOOK REVIEW

General Chemistry Principles and Introduction to Chemistry, Fourth order of chapters after the first four without Structure, Third Edition, SI Version Edition penalty. . A final point; this book does not have that James E. Brady and Gerard E Hum/s- T. R. Dickson, John Wiley a Sons, Som- fourth edition the- author -listened -to-ev- ton, John Wifey & Sons, Somerset, NJ, erset, NJ, 1983. xvli + 540 pp. Figs, and ery-advisor-aroimd look. It is a polished, 1983. xix + 826 pp. Figs, and tables. 2,2 X tables. 19 X 24 cm. $25.95. well-written, attractively designed textbook. 26 cm. $30.95. It is recommended for those who are faced with the challenge of teaching the course for The appearance of an SI version of this This textbook, intended for a one-term which it is written. respected textbook [see my review in this course in chemistry, is supposed to fulfill the Deaii F. Martin Journal, 60, A103 (1983)] is a sign of a needs of two different groups of students— University of South Florida healthy sales picture, which for the admirable those who need a foundation for additional Tampa, FL 33620 text under review is altogether deserved. courses in chemistry and those who wish to Unfortunately, however, the need for two have only an introductory course. It is a alternative versions of first-year textbooks challenge to teach both groups, and.it is a reflect* a deplorable lack of agreement among significant challenge to find an appropriate chemists over the basic grammar and spelling textbook. of our science. At this time no consensus has The author recognizes the need to provide yet been reached on the names that should be students with an appropriate background in given to the well-defined physical quantities systems of measurement and problem solv- and the symbols for those names, the names ing. This is handled well through the factor- Practice of Thin Layer given to well-defined units and the symbols label method in the first chapter and through for those names, and the rules for the ex- the use of three appendices. Chromafography. Second Edition pression of relations involving numerical Chapter two coverB the chemical elements Joseph C. Touchstone and Murrell F. Dob- values between such physical quantities and bins, John Wiley & Sons, Somerset, NJ, such units. Thus, students of chemistry at all (nature of matter, atomic theory, nuclear atom, isotopes, and atomic weights), chapter 1983. iii + 405 pp. Figs, and tables. 16 X levels are currently taught an incredible 23.5 cm. $40.00. mishmash of names and symbols, depending three covers compounds and formulas, and on the whim of the particular instructor. In chapter four looks at atomic structure and the this situation we look to editors and textbook periodic tabJa, including electronic configu- The authors present a follow-up volume authors for the leadership which will lead us rations. of their successful first edition which was to a more logical and rational future. Against Subsequent chapters cover chemical published in 1978. The book consists of 16 this is the conservatism of the professoriate bonds, chemical nomenclature, chemical re- chapters and is intended primarily for prac- who, after all, can control at least the text- actions and equations, chemical stoiehiom- ticing chromatographers. It contains much book market by exercising the power not to etry, gases, water and solutions, solution dy- "how to" information and is full of practical adopt. namics and chemical equilibrium, acids, and advice. bases, oxidation and reduction, liquids and Comparing the second to the first edition, Even in this version of the excellent text solids, nuclear energy, organic chemistry, and one finds that the majority of the chapters under review, Professor Heikkinen, a well- biochemistry. was left essentially untouched. In many cases practiced chemical educator, has retained the In short, most significant topics of general the chapters are identical, including the lists standard atmosphere (atm) as a convenient chemistry are considered (though, obviously, of references. The only significant changes synonym for 101,325 N m~2 (101.325 kPa), a in limited detail). At first glance, then it were made in Chapter 4 dealing with sample even though the N m~ (pascal) is used as the might seem that the book is written for the preparation and application, and Chapter 10 Si-derived unit of pressure throughout the second student group. Actually, the author which has been relabelled from "Radioactive text. has faced the dilemma of what to include and Procedures" to "Procedures for Radioactiv- This popular and serious textbook is highly has responded by providing all students with ity." The authors have, however, paid tribute recommended. an honest view of chemistry as the basic, ex- to 2 new developments, revise phase tech- citing, relevant central science that it is. J. J. Zuckerman University of Oklahoma There is a tot of material here, but it is weii Norman, OK 73019 presented, and the instructor can alter the (Continued on page A114)

-Reviewed in this issue- Reviewer James E. Brady and Gerard E. Humiston, General Chemistry Principles and Structure, Third Edition, Sf Version J. J. Zuckerman A113 T- R. Discon, Introduction to Chemistry, Fourth Edition Dean F. Martin A113 Joseph C. Touchstone and Murrell F. Dobbins, Practice of Thin Layer Chromatography, Second Edition Wolfgang Bertsch A113 Titles of Interest A114 Continuing Series A114

Volume 61 Number 3 March 1984 A113 APPARATUS CHEMICALS NEW JOURNAL EQUIPMENT chem ed buyer'/ guide SERVICES ANNOUNCEMENT Drying Technology and International [THE CHEMISTRY TEST MAKEIP Journal, Volume 1, Number 1 I Make Any Size Tests On Copyable Disks Carl W. Hail {Editor}, Marcel Dekker, Inc., New York, NY, 1983. 163 pp. Figs, and ta- bies. 15 X 23 cm. Two issues per volume; STOP j COMPUTER CHEMISTRY Institutional rate, $95.00; individual rate, SPILLS! $47.50. Stabilize j 15 CA.I. Programs - Apple & TRS-80 Suction Flasks | HIGH SCHOOL & JR. COLLEGE TITIES Of INTEREST with Vinvl Coated History of Clinical Chemistry LEAD OONUT I For information Write Or Call 7 sizes J. BuUner, (Editor) Waiter de Gruyter and j J & S SOFTWARE Co., Berifrt, Germany, 1983. 91 pp. Figs, $5.59 tO $3IJ> 140 Reid Avenue and tables. 18.5 X 26.5 cm. $44.50. Port Washington, N.Y. ttO50 Cheltenham 1 This volume is a collection of eight (8> pa- I 516-944-9304 • PA 19012 pers on the history of Clinical Chemistry that originally appeared in the Journal of Clinical Chemistry and Clinical Biochemistry in 1981 RAPID ELEMENTAL ANALYSIS AND and 1982. UNDERGRADUATE TEACHING I APPLE II -TEST TITLES OF INTEREST Vreelarw! Spectroscope • CREATE-A Symposium Easy to dperate It's here! A computer program that Built-in Standards fo makes perfectly formatted chemistry • Analytical Chemistry Symposia Series, At! the Elements tests in 10 minutes. Use disks ofH Volume 15, Computer Applications in Direct Reading prepared questions or write yourown. g Chemistry 6000 chemistry Calf or write for trso Application Note questions available S. R. Heller and B. Potenzorte, (Editors), arid free viewn/j of movte film. Elsevier Science Publishers, New York, SPECTREX CORPORATION SSSOO • CROSS EDUCATIONAL SOFTWARE NY, 1983. xii + 394 pp. Figs, and tables. 3594 Haven Ave., Redwood City, CA 94063 • P.O. Box 1536, Ruston, LA71270 17 X 24.5 cm. Phoie[415J 365-6567 • (318)255-8921 Topics Covered: The Neglected Ingredi- ent in Chemical Computer Systems; Di- Microcomputer Software rections In Macromolecular Structure for General Chemistry USE Representation and Display; Some As- Free brochure listing

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