| ? | ? | ? | ? | ? |Tanta- |Tung- | ? |Osmium | | | | | | |lum |sten | |Os = | | | | | | |Ta = |W = | |190·9 | | | | | | |181·5 |184·0 | |Iridium | | | | | | | | | |Ir = | | | | | | | | | |193·1 | | | | | | | | | |Platinum| | | | | | | | | |Pt = | | | | | | | | | |195·2 | +-------+-------+-------+-------+-------+-------+-------+-------+--------+ | |Gold |Mercury|Thal- |Lead |Bismuth|Polo- | ? | | | | | |lium | | |nium | | | | |Au = |Hg = |Tl = |Pb = |Bi = |(210) | | | | |197·2 |200·6 |204·0 |207·20 |208·0 | | | | +-------+-------+-------+-------+-------+-------+-------+-------+--------+ |Emana- | ? |Radium |Acti- |Thorium|Ekatan-|Uranium| ? | ? | |tion | | |nium | |talum | | | | |(Niton)| |Ra = | ? |Th = | ? |U = | | | | 222·0 | |226·0 | |232·15 | |238·2 | | | +-------+-------+-------+-------+-------+-------+-------+-------+--------+ NOTES. There are several somewhat different forms of this Periodic Table. This is one of the simplest, but it lacks certain advantages of some of the more complicated forms. The atomic weights given are those of the International Atomic Weights Committee for 1920-1. They are calculated on the basis, Oxygen = 16. The number of decimal places given in each case indicates the degree of accuracy with which each atomic weight has been determined. The letter or letters underneath the name of each element is the symbol by which it is invariably designated by chemists. The number above each column indicates the valency which the elements of each group exhibit towards oxygen. Many of the elements are exceptional in this respect. [a]: The exact position of Hydrogen is in dispute. [b]: The positions of Argon and Potassium have been inverted in order that these elements may fall in the right columns with the elements they resemble; [d]: so also have the positions of Tellurium and Iodine. [c]: The whole of “Group 8” forms an exception to the Table. [e]: There are a number of ill-defined rare earth metals with atomic weights lying between those of Cerium and Tantalum. They all appear to resemble the elements of “Group 3,” so that their positions in the Table cannot be decided with accuracy.