Argon atomic weight

Any of the inert gases could be used for GTAW However, only helium (atomic weight 4) and argon (atomic weight 40) are used commercially, because they are much more plentiful and much less costly than the other inert gases. Typical flow rates are 15 to 40 cubic feet per hour (cfh). 

Argon (atomic weight 39.948) has three stable isotopes of mass numbers 36, 38, and 40, which occur in a relative abundance in the atmosphere in the ratios 338 63 100,000, respectively. 

The atomic weight of an element is a weighted average of the mass of the naturally occurring isotopes of that element. Therefore, the atoms in a naturally occurring sample of argon must be heavier than the atoms in a naturally occurring sample of potassium. 

Atoms of argon have 18 protons, whereas atoms of potassium have 19 protons. In order for the atomic weight of argon to be greater than that of potassium, argon atoms must have more neutrons. 

From these data, we can see that argon would have a higher atomic weight than potassium. 

Soon after hearing of the discovery of argon, Lecoq de Boisbaudran predicted that it might belong to a family of absolutely inert elements all of which were then unknown, and that their atomic weights would be 20.0945, 36.40 0.08, 84.01 0.20, and 132.71 0.15. He also predicted that the first two of these elements would be more abundant than the others (33, 34). 

Dr. Travers, who was born in London on January 24, 1872, studied at University College, and received his doctorate in 1893. Soon after this he became intensely interested in Sir William Ramsays remarkable new elements and in the possibility of discovering another one between helium and argon and two others of higher atomic weight than argon. 

Sir William Ramsay, 1852-1916. Scottish chemist and physicist who, with Lord Rayleigh and M. W. Travers, discovered the inert gases helium, neon, argon, krypton, and xenon. He also made a remarkable determination of the atomic weight of radon (radium emanation), the heaviest of the inert gases. 

Thus Moseley s series is almost the same as Mendeleev s series of increasing atomic weights. When, however, the elements are arranged, not according to their atomic weights, but according to their atomic numbers (Moseley numbers), the discrepancies between argon and potassium and between iodine and tellurium disappear (10). 

Dmitri Mendeleyev (1834-1907), a Russian scientist and creator of the modern periodic table, discovered that if elements were lined up according to atomic weights and arranged in rows of 2, 8, 18, and 32, atoms with similar chemical and physical properties appeared in the same column. However, there were some exceptions. Argon and potassium were out of place. So were iodine and tellurium. Mendeleyev thought his relative weights were incorrect. 

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