The Periodic Table of the Elements The president of the Inorganic Chemistry Division, atomic number was the same as the number of protons Gerd Rosenblatt, recognizing that the periodic table in each element. of the elements found in the “Red Book” A problem for Mendeleev’s table was the position- (Nomenclature of Inorganic Chemistry, published in ing of the rare earth or lanthanoid* elements. These 1985) needed some updating—particularly elements elements had properties and atomic weight values above 103, including element 110 (darmstadtium)— similar to one another but that did not follow the reg- made a formal request to Norman Holden and Tyler ularities of the table. Eventually, they were placed in a Coplen to prepare an updated table. This table can be separate area below the main table. found below, on the IUPAC Web site, and as a tear-off The Danish physicist Niels Henrik David Bohr pro- on the inside back cover of this issue. posed his electronic orbital structure of the atom in 1921, which explained the problem of the rare earth by Norman Holden and Ty Coplen elements. The electrons in the outermost and the penultimate orbits are called valence electrons since generally their actions account for the valence of the he Russian chemist Dmitri Ivanovich Mendeleev element (i.e., electrons capable of taking part in the constructed his original periodic table in 1869 links between atoms). Chemical behavior of an ele- Tusing as its organizing principle his formulation ment depends on its valence electrons, so that when of the periodic law: if the chemical elements are only inner orbit electrons are changing from one ele- arranged in the ascending order of their atomic ment to another, there is not much difference in the weights, then at certain regular intervals (periods) chemical properties between the elements. elements occur having similar chemical and physical The elements from actinium through uranium (along properties. with neptunium through curium when they were first synthesized) were originally placed with the main table Mendeleev sensed that chemical behavior was more elements, in spite of problems with their chemical fundamental than atomic weight and left empty spaces properties. In 1946, the American chemist Glenn in his table when chemical properties did not fit. He predicted that these miss- 1 1 ing elements would be discovered with H hydrogen appropriate atomic weight values and 1.007 94(7) 2 Key: having the required properties. When 3 4 atomic number Li Be Symbol lithium beryllium name gallium, scandium, and germanium were 6.941(2) 9.012 182(3) standard atomic weight discovered over the next 15 years with 11 12 Na Mg the properties that Mendeleev pre- sodium magnesium 3456789101112 22.989 770(2) 24.3050(6) dicted, the scientific world began to 19 20 21 22 23 24 25 26 27 28 29 30 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn take his periodic table seriously. potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc 39.0983(1) 40.078(4) 44.955 910(8) 47.867(1) 50.9415(1) 51.9961(6) 54.938 049(9) 55.845(2) 58.933 200(9) 58.6934(2) 63.546(3) 65.409(4) In 1913, the English physicist Henry 37 38 39 40 41 42 43 44 45 46 47 48 Gwyn Jeffreys Moseley compared the Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium energy of the X-ray spectral lines of var- 85.4678(3) 87.62(1) 88.905 85(2) 91.224(2) 92.906 38(2) 95.94(2) [97.9072] 101.07(2) 102.905 50(2) 106.42(1) 107.8682(2) 112.411(8) 55 56 57-71 72 73 74 75 76 77 78 79 80 ious elements against their atomic Cs Ba lanthanoids Hf Ta W Re Os Ir Pt Au Hg caesium barium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury weight. He obtained an approximate 132.905 45(2) 137.327(7) 178.49(2) 180.9479(1) 183.84(1) 186.207(1) 190.23(3) 192.217(3) 195.078(2) 196.966 55(2) 200.59(2) 87 88 89-103 104 105 106 107 108 109 110 111 straight-line graph. To avoid breaks in Fr Ra actinoids Rf Db Sg Bh Hs Mt Ds Uuu francium radium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium unununium this graph, he found it necessary to [223.0197] [226.0254] [261.1088] [262.1141] [266.1219] [264.12] [277] [268.1388] [271] [272] place elements in the order demanded 57 58 59 60 61 62 63 64 65 66 by the chemical properties rather than La Ce Pr Nd Pm Sm Eu Gd Tb Dy lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium increasing atomic weight. Moseley’s 138.9055(2) 140.116(1) 140.907 65(2) 144.24(3) [144.9127] 150.36(3) 151.964(1) 157.25(3) 158.925 34(2) 162.500(1) curve of X-ray lines indicated that every 89 90 91 92 93 94 95 96 97 98 Ac Th Pa U Np Pu Am Cm Bk Cf element has a constant value, its ordinal actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium or atomic number, that increases by a [227.0277] 232.0381(1) 231.035 88(2) 238.028 91(3) [237.0482] [244.0642] [243.0614] [247.0704] [247.0703] [251.0796] constant amount from element to ele- For a printable version of this table, see <www.iupac.org/reports/periodic_table/>. ment. In 1920, Chadwick showed that the A tear-off copy is attached to the backcover of this issue of CI. 8 CHEMISTRY International January-February 2004 Theodore Seaborg suggested that these elements report provides table 3 with either the atomic mass or, formed an actinoid group similar to the lanthanoid. when that parameter is unknown, merely the atomic Lawrencium completed the actinoid series and element mass number (number of protons and neutrons in the 104 was placed in the seventh row of the main table. nucleus) of the most stable nuclide of that element There were conflicting claims of who first synthe- (i.e., the nuclide having the longest half-life). This sized element 104 and the next few elements of the value from table 3 of the report is shown on the peri- table for almost a quarter century. During this long odic table in square brackets for many of the ele- impasse, Joseph Chatt (of IUPAC’s Inorganic ments, including all elements above uranium. Thus, Chemistry Division) suggested the use of a Greco- element 100 is listed as “[257.0951].” Otherwise, the Roman naming scheme to provide a provisional IUPAC mass number of the longest lived nuclide is listed, name with a three letter symbol (e.g., element 111 such as [277] for hassium. One element deserves a would have the name unununium with a symbol Uuu). special comment in this regard. Element 110, darm- Eventually, a joint working party from IUPAC and from stadtium (Ds), is listed in table 3 of the report [281]. the International Union of Pure and Applied Physics Because the half-life of 1.6 min for 281Ds was deter- (IUPAP) was formed to review the scientific data for mined from only a single decay, it was decided elements 104 through 109 and to resolve the impasse. instead to give in the periodic table the mass number The joint IUPAC/IUPAP working party decided to con- of a nuclide that has the longest half-life and that con- tinue resolving the problem of determining the first firms the discovery of Ds. This is 271Ds; thus, [271] is synthesizer for future elements. The group determined listed for element 110. that element 110 was initially made by the German Element 111 has also been acknowledged by the joint group at the Heavy Ion facility in Darmstadt, Germany. IUPAC/IUPAP working party to have first been synthe- The Germans suggested the name darmstadtium with sized by the same German group at Darmstadt, but a the symbol Ds, which are now accepted both by name has not yet been suggested. It is shown on the IUPAC and IUPAP. table with its IUPAC provisional name and symbol “Uuu.” In keeping with the traditional use of atomic weight The elements with atomic numbers 112, 114, and 116 have values in the peri- been reported in the scientific literature, but have not 18 odic table, the lat- yet been authenticated by the IUPAC/IUPAP working 2 He est (2001) IUPAC party, so they do not yet merit a place in the table. helium 13 14 15 16 17 4.002 602(2) approved Standard Finally, for American readers, it is noted that alter- 5 6 7 8 9 10 Atomic Weight val- nate English language spellings for the names of alu- B C N O F Ne boron carbon nitrogen oxygen fluorine neon 10.811(7) 12.0107(8) 14.0067(2) 15.9994(3) 18.998 4032(5) 20.1797(6) ues are listed on the minum and cesium are used in the USA and do not 13 14 15 16 17 18 table with the constitute erroneous spellings. Al Si P S Cl Ar aluminium silicon phosphorus sulfur chlorine argon uncertainty in the 26.981 538(2) 28.0855(3) 30.973 761(2) 32.065(5) 35.453(2) 39.948(1) 31 32 33 34 35 36 last figure shown in *The 1985 “Red Book” (p.