Pure & 4pl. Chem., Vol. 56, No. 6, pp. 695—768, 1984. 0033—4545184 $3.00+0.00 Printed in Great Britain. Pergamon Press Ltd. ©1984 IUPAC INTERNATIONALUNION OF PURE AND APPLIED CHEMISTRY INORGANIC CHEMISTRY DIVISION COMMISSION ON ATOMIC WEIGHTS AND ISOTOPIC ABUNDANCES ELEMENT BY ELEMENT REVIEW OF THEIR ATOMIC WEIGHTS Prepared by Subcommittee on Assessment of Isotopic Composition of the Elements whose Membership during its preparation (1981—83) was as given below Editorial Coordinator: H. S. PEISER"2 Chairman, Commission: N. E. HOLDEN1 Chairman, Subcommittee: P. DE BIEVRE3 Secretary, Subcommittee: I. L. BARNES2 Members: R. HAGEMANN4, J. R. DE LAETER5, T. J. MURPHY2, E. ROTH4, M. SHIMA6, H. G. THODE7 'Brookhaven National Laboratory, Upton, LI, NY, USA 2National Bureau of Standards, Washington, DC, USA 3Central Bureau for Nuclear Measurements, Geel, Belgium 4Centre d'Etudes Nucleaires de Saclay, Gif-sur-Yvette, France 5Western Australian Institute of Technology, Perth, Australia 6National Science Museum, Tokyo, Japan 7McMaster University, Hamilton, Canada TABLE OF CONTENTS Page Acknowledgments 697 Part I. Introduction 698 1. Preamble 698 2. The Previous Element-by-Element Review 698 3. The IUPAC Tables 699 4. Reasons for a New Element-by-Element Review 700 5. The Assignment of Uncertainties and their Indication by the Tabulated Standard Atomic Weight 700 6. "Abnormal' Materials 703 7. The Mononuclidic Elements 705 8. Chemical Determinations of Atomic Weights 707 9. Mass Spectrometric Techniques for the Determination of Atomic Weights 708 10. Possible Future Techniques of Atomic-Weight Determinations 709 11. Radionuclides in Normal and "Abnormal" Materials 711 12. Aims and Format of the Sections in Part II on Each of the Elements 712 13. Changes in Atomic Weights and Their Uncertainties 713 References (for Part I) 716 Part II. The Elements (in ascending order of atomic number) 717 Page Page Aluminium Mercury 765 Antimony (Stibium). Molybdenum 744 Argon Neodymium 755 Arsenic Neon 724 Barium Nickel 735 Beryllium Niobium 743 Bismuth Ni trogen 722 Boron Osmium 763 Bromine Oxygen 723 Cadmium Palladium 746 Caesium Phosphorus 727 Calcium Platinum 764 Carbon Potassium (Kal ium). 729 Cerium Praseodyrni urn. 754 Chlorine Rhenium 762 Chromi um Rhodium 745 Cobalt Rubidium 741 Copper Ruthenium 745 Dysprosium Samari urn 755 Erbium Scandi urn 730 Europium Selenium 739 Fluorine Silicon 726 Gadolinium Silver 746 Gallium Sodium (Natriurn). 725 Germanium Strontium 742 Gold Sulfur 727 Hafnium Tantalum 761 Helium Tellurium 750 Holmium Terbium 757 Hydrogen Thal 1 ium 765 Indium Thorium 767 Iodine Thulium 759 Iridium Tin 749 Iron Titanium 731 Krypton Tungsten (Wolfram). 762 Lanthanum Uranium 768 Lead Vanadiurn 732 Lithium Xenon 752 Luteti urn Ytterbium 759 Magnesium Yttrium 742 Manganese Zinc 736 Zirconium 743 696 Element by element review of their atomic weights 697 ELEMENT BY ELEMENT REVIEW OF THEIR ATOMIC WEIGHTS Endorsed by the Commission on Atomic Weights and Isotopic Abundance (CAWIA), of the International Union of Pure and Applied Chemistry (IUPAC) Abstract —TheIUPAC "standard' atomic weights of the terrestrially occurring chemical elements are individually reviewed tracing changes during the past 25 years. Emphasized is the relevant published scientific evidence which in each case constitutes the basis for the expert judgment by the responsible IUPAC Commission. It biennially reports on, recommends, and tabulates the best values of these atomic weights with an implied judgment of their individual reliability. In the introductory part of this Review the history of atomic—weight determinations is sketched. The IUPAC leadership in this data— evaluation project is described as it benefits science, technology, and trade. The remaining experimental uncertainties and natural variabilities are discussed. The treatment of abnormal materials is explained. The principal techniques for determining atomic weights are outlined. The effects of naturally occurring radioactive nuclides are characterized in their essentials. ACKNOWLEDGMENT S The International Union of Pure and Applied Chemistry has since its founding encouraged and supported the assessment and dissemination of atomic—weight data. This function is assigned to its Commission for Atomic Weights and Isotopic Abundances (CAWIA) which in 1981 decided that the tine had cone to prepare an Element—by—Element Review of their Atomic Weights. That Commission accordingly entrusted to the Subcommittee for the Assessment of the Isotopic Composition of the Elements (SAIC), the preparation of this Review. This task could not have been undertaken without continuing interest and backing from the employing organizations of all SAIC members, who are the authors of this Review. Very special acknowledgments should be expressed to those organizations which also hosted recent meetings of SAIC. These host organizations are: the Central Bureau for Nuclear Measurements of the Commission of European Communities, the Brookhaven National Laboratory, and the National Bureau of Standards. They made important meeting facilities available to the authors including computer services which enabled the SAIC members to compute atomic weights and associated uncertainties on the spot as the joint assessment of published information proceeded during these meetings. The encouragement of the Western Australian Institute of Technology, the Centre d'Etudes Nuclaires de Saclay (of France), the National Science Museum (of Japan), and McMaster University (of Canada) is also sincerely appreciated. Unforgettable to the authors is the late Dr. Angus E. Cameron, formerly of the Oak Ridge National Laboratory. He was not only one of two authors of the previous element—by—element review but also —exceptfor his sudden and unexpected death —wouldhave been a co—author of this Review. During the intervening period, he was constantly active in the field, his views have been an inspiration to all the authors, and he took part in the initial planning for this Review. The authors owe Gus Cameron, their former colleague and friend, lasting gratitude and profound respect. Acknowledgment is also due to Professor A. H. Wapstra, Dr. K. Bos, and their publishers, the Academic Press, for permission to quote extensively from The 1977 Atomic Mass Evaluation Tables. The authors express thanks to D. Garvin and N. N. Greenwood for helpful comments on portions of the manuscript. Tables 3 and 4 were typed at Brookhaven National Laboratory. Much appreciation is expressed to Gelene Hensley, Anne Lawrence, and Joy Shoemaker at the National Bureau of Standards who typed the text and skillfully applied word—processing technology to prepare a concise document. 698 CONNISSION ON ATOMIC WEIGHTS AND ISOTOPIC ABUNDANCES PART I. INTRODUCTION 1. Preamble Although theories postulatimg the existence of atoms, indivisible smallest particles of materials, are deeply rooted in Greek metaphysics of ancient times, the wide acceptance of the atomic theory lies surprisingly late in the last century. John Dalton early in that century had published the first atomic—weight tables, but their values are today hard to recognize. Since then the determination of these numbers has attracted the efforts and skills of many famous chemists. Atomic weights are needed in science, technology, trade and commerce. In particular, no use can be made of the results of analytical chemistry without atomic weights which relate mass to molar quantities. The American Chemistry Society in 1894 published F. W. Clarke's remarkably accurate standard table of atomic weights, followed a few years later by a similar German table published by the Deutsche Chemische Gesellschaft. Together with D. I. Medeleev's periodic table of the elements, the foundations were thus laid for the development of modern chemistry. The importance of a consistent scale and internationally recognized values for the atomic weights now led to the formation of the first international committee which for practical reasons in communication elected an action committee of three: F. W. Clarke (U.S.A.), T. E. Thorpe (England), and K. Seubert (Germany). They published annual revisions of the atomic weights from 1903 until the first World War disrupted their efforts. In the meantime H. Moissan had joined the small Committee as representative of France to be replaced after his death by G. Urbain. Seubert resigned in 1906 and was replaced by W. Ostwald, with whom communication was not resumed after 1916. In 1913 this Committee affiliated itself to the International Association of Chemical Societies and in 1919 subordinated itself to the Inter— national Union of Pure and Applied Chemistry, which had just been constituted. In 1921 the Committee was enlarged and renamed "Committee of the Chemical Elements" with enhanced terms of reference, but redivided in 1930 with the formation of the "Atomic Weights Committee" plus two other committees. This "Atomic Weights Committee" went through further minor reorgani— zations and changes in name until in 1979 it became the present Commission on Atomic Weights and Isotopic Abundances (CAWIA). Since 1930 CAWIA and its predecessor committees have been chaired successively by G. Baxter (U.S.A.), E. Wichers (U.S.A.), N. N. Greenwood (U.K.), E. Roth (France), N. E. Holden (U.S.A.), and R. L. Martin (Australia). IUPAC from its inception has expended, and as the Commission's parent organization continues to undertake, much effort for the careful evaluation and dissemination of atomic weights and their uncertainties derived from