Gram Atomic Mass, Gram Molecular Mass and Formula Mass

As we know that all substances are made up of atoms, molecules or formula units. Their masses are reffered to as atomic masses and formula masses respectively and are expressed in amu. But these masses can also be expressed in other units as well. When masses are  expressed in grams, they are termed as following:

1. Gram atomic masses
2. Gram molecular masses
3. Gram formula masses

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Gram atomic mass

The atomic mass of an element expressed in grams is called gram atom. It is also called a mole.

1 gram atom of hydrogen  =  1.008 g  =  1 mole of hygrogen atoms

1 gram atom of carbon = 12.0 g  = 1 mole of carbon

It means that 1 gram atom of different elements has different masses.

Gram molecular mass

The molecular mass of an element or a compound expressed in grams is called gram molecule. It is also called a mole.

1 gram molecule of H₂  = 2.0 g  = 1 mole of hydrogen molecule

1 gram molecule of H₂O  = 18.0 g  =  1 mole of water

1 gram molecule of H₂SO₄ = 98.0 g  =  1 mole of Sulphuric acid

Gram formula mass

The formula mass of an ionic compound expressed in grams is called gram formula. This is also called a mole. For

1 gram formula of NaCl  =  58.5 g  = 1 mole of sodium chloride

1 gram formula of CaCO₃ = 100 g = 1 mole of calcium carbonate.