Gram-atomic weight, definition

The mole (abbreviated mol) is defined as the amount of a substance comprising as many elementary units as there are atoms in 12 g of The definition of the mole is equivalent to the statement that the mass of one mole of a pure substance in grams is numerically equal to its molecular weight calculated from the standard table of atomic weights, in which the atomic weight of carbon is given as 12.01115. This number differs from 12 because it applies to the natural isotopic mixture of carbon rather than to pure... 

The term mole was first introduced by Wilhelm Ostwald in 1901. It is derived from the Latin for mass, hump, or pile (the term molecule, introduced by Pierre Gassendh in the early seventeenth century has the same root presumably it means a mass of atoms). Specifically, Ostwald used the term to represent the formula weight of a substance in grams 36.5 g of HCl is one mole. The formal definition of the mole adopted by the Fourteenth Conference Generale des Poids et Mesures in 1971 is the amount of a substance of a system that contains as many elementary entities as there are atoms in 0.012 kilograms of carbon-12. The rich irony is that Ostwald fiercely resisted the atomic concept at the time Boltzmann committed suicide in 1906 but his mole is now defined explicitly in terms of atoms. 

They could not chemically trace the infinitesimal accumulation of silicon. Joliot explained why in 1935, when he and his wife accepted the Nobel Prize in Chemistry for their discovery The yield of these transmutations is very small, and the weights of elements formed. .. are less than 10 [grams], representing at most a few million atoms —too few to find by chemical reaction alone. But they could trace the radioactivity of the phosphorus with a Geiger counter. If it did indeed signal the artificial transmutation of some of the aluminum to phosphorus, they should be able to separate the two different elements chemically. The radioactivity would go with the new phosphorus and leave the untransmuted aluminum behind. But they needed a definitive separation that could be carried out within three minutes, before the faint induced radioactivity faded below their Geiger counter s threshold. 

The precise ratio of atoms of different elements in a compound is responsible for the Law of Definite Composition, also called the Law of Constant Composition. This law states that any compound is always made up of elements in the same proportion by mass (weight). The source of the compound does not matter. For example, 100 grams of pure water always contains 11.1 grams of hydrogen and 88.9 grams of oxygen. It makes no difference if the water comes from a pond in Kansas, a river in South America, a lake in the Alps, or a comet in the far reaches of the solar... 

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