Gram-Atomic Mass and Gram-Molecular Mass

Historically, the terms gram-atomic mass (or gram-atom), gram-molecular mass (or gram-mole), and gram-ionic mass (or gram-ion), were used to represent the mass of one Avogadro’s number of atom, molecule or ion respectively.

These terms are no longer used.

The term which is used for representing one Avogadro‘s number of chemical units, now-a-days is called a mole. Thus, for any substance, the practical unit presently used for describing the atomic and molecular masses is mole.

Gram-Atomic mass

The gram atomic mass is defined as

“the number of grams of an element numerically equal to its relative atomic mass is termed as the gram-atomic mass of that element.”

For example, the relative atomic mass of hydrogen is 1.008. So, the gram-atomic mass of hydrogen is 1.008 g.

In terms of the mole concept, the gram-atomic mass of an element is equal to mass (in grams) of 6.02 × 10²³ atoms of that element. The number 6.02 × 10²³ is termed as the Avogadro’s number. So, the gram-atomic mass of an element is equal to mass (in gram units) of the Avogadro’s number of atoms of the element.

1 gram-atomic mass = 1 gram-atom = Mass of 6.02 × 10²³ atoms of the substance

Gram-Molecular mass

The gram molecular mass is defined as,

“the number of grams of a substance numerically equal to its relative molecular mass is termed as the gram-molecular mass of that element.”

For example, the relative molecular mass of hydrogen is 2.016. So, the gram-molecular mass of hydrogen is 2.016 g.

In terms of the mole concept, the gram-molecular mass of a substance is equal to the mass (in gram units) of 6.02 × 10²³ molecules of that substance. The number 6.02 × 10²³ is termed as the Avogadro’s number. So, the gram-molecular mass of a substance is equal to the mass (in gram units) of the Avogadro’s number of molecules of that substance.

1 gram-molecular mass = 1 gram-mole

              = Mass of 6.02 × 10²³ molecules of the substance

Gram-Ion mass

In terms of the mole concept, the gram-ion mass of an ion is equal to the mass (in gram units) of 6.02 × 10²³ ions of that type. Since the number 6.02 × 10²³ is termed as the Avogadro’s number of that ion,

1 gram-ionic mass = 1 gram-ion = Mass of 6.02 × 10²³ ions

   = Mass of Avogadro’s number of that ion