gram-molecular weight

(chemistry) The molecular weight of compound expressed in grams, that is, the molecular weight on a scale on which the atomic weight of carbon-12 isotope is taken as 12 exactly.

The molecular weight of an element or compound expressed in grams (g), that is, the molecular weight on a scale on which the atomic weight of the ¹²C isotope of carbon is taken as 12 exactly. This replaces the earlier scale on which the atomic weight of oxygen was taken as 16.00 g. In the International System of Units, gram-molecular weight is replaced by the mole.

The ratio of the gram-molecular weights of any two elements or compounds must be identical with the ratio of the absolute weights of their individual molecules. Therefore, the gram-molecular weights of all elements or compounds contain the same number of molecules. This number, called the Avogadro number, N, is 6.022 × 10²³. See also Molecular weight; Relative molecular mass.

See mole³ (sense ).