Gold atomic weight

All elements, by definition, have a unique proton number, but some also have a unique number of neutrons (at least, in naturally occurring forms) and therefore a unique atomic weight - examples are gold (Au Z = 79, N = 118, giving A =197), bismuth (Bi Z = 83, N = 126, A = 209), and at the lighter end of the scale, fluorine (F Z = 9, N = 10, A = 19) and sodium (Na Z = 11, N= 12, A = 23). Such behavior is, however, rare in the periodic table, where the vast majority of natural stable elements can exist with two or more different neutron numbers in their nucleus. These are termed isotopes. Isotopes of the same element have the same number of protons in their nucleus (and hence orbital electrons, and hence chemical properties), but... 

Hafnium had lain hidden for untold centuries, not because of its rarity but because of its dose similarity to zirconium (16), and when Professor von Hevesy examined some historic museum specimens of zirconium compounds which had been prepared by Julius Thomsen, C. F. Rammelsberg, A. E. Nordenskjold, J.-C. G. de Marignac, and other experts on the chemistry of zirconium, he found that they contained from 1 to 5 per cent of the new element (26, 27). The latter is far more abundant than silver or gold. Since the earlier chemists were unable to prepare zirconium compounds free from hafnium, the discovery of the new element necessitated a revision of the atomic weight of zirconium (24, 28). Some of the minerals were of nepheline syenitic and some of granitic origin (20). Hafnium and zirconium are so closely related chemically and so closely associated in the mineral realm that their separation is even more difficult than that of niobium (columbium) and tantalum (29). The ratio of hafnium to zirconium is not the same in all minerals. 

The metals copper, silver, and gold show a marked tendency to form double and complex salts, the tendency being greatest in the case of gold, the member of the group with highest atomic weight. 

John Dalton (1766-1844), a science teacher in England, combined the idea of the atom and Lavoisier s new definition of elements. Fie suggested that there were different kinds of atoms behind different elements. In this case, gold was built out of gold atoms, and lead was built out of lead atoms. Dalton also figured out a way to estimate the weight of each kind of atom. Other... 

An element can be defined by the number of protons in its atoms. All hydrogen atoms have only one proton, whereas all iron atoms have 26 protons and all gold atoms have 47 protons. The number of neutrons can vary, and there are usually more neutrons than protons in elements heavier than aluminum. Atoms of the same element that have different atomic weights due to different numbers of neutrons in the nucleus are called isotopes. Most of the weight of an atom comes from its protons and neutrons. Protons and neutrons have nearly the same mass, or to put it another way, they contain nearly the same amounts of matter. A proton has almost 2,000 times more mass than an electron. 

Historical.—In his tables published in 1818 Berzelius4 gave 31-36 as the atomic weight of phosphorus. Other values obtained before and after this time did not agree even so well as this with the value accepted to-day. The reactions principally employed in this early period were the displacement of gold and silver from their chloride and sulphate respectively by elementary phosphorus. These reactions,... 

According to Brauner,1 the results marked with an asterisk ( ) and obtained by Kriiss, Thorpe and Laurie, and Mallet, are the most reliable. Their arithmetic mean is Au=197-208. Employing the value 107-883 for the atomic weight of "silver, Brauner has calculated from them a mean value for the atomic weight of gold, Au=197-20. 

The value given in the International Atomic Weight Tables for gold at present is 197.2 it is not unlikely that this will soon be revised to the mass-spectrographic value by the International Committee. 

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