The terms "gram atomic weight" and "gram molecular weight" are older terminologies that were used before the concept of molar mass became widely adopted in chemistry. While the use of these terms has diminished in modern practice, they are still occasionally encountered, especially in older literature or when referring to historical contexts.
The reason for the persistence of these older terms can be attributed to tradition and historical continuity. Chemistry has a long history, and the development of concepts and terminology has evolved over time. The terms "gram atomic weight" and "gram molecular weight" were widely used in the past, and although the concept they represent is essentially the same as molar mass, the older terms continue to be recognized.
However, it is worth noting that the International Union of Pure and Applied Chemistry (IUPAC) has recommended the use of the term "molar mass" as the preferred and more precise terminology to describe the mass of a mole of a substance. Molar mass is an absolute quantity expressed in grams per mole (g/mol). It represents the mass of one mole of a substance, and it is numerically equal to the relative isotopic mass (atomic weight) expressed in grams.
The term "molar mass" is now widely used in modern chemistry textbooks, research papers, and scientific communication. It provides a clearer and more standardized description of the mass of a substance on a per-mole basis, facilitating calculations and comparisons across different elements and compounds.
While the terms "gram atomic weight" and "gram molecular weight" may still occasionally appear, especially in older references, the preferred and more precise terminology today is "molar mass."