# Where can formula mass be applicable?

Formula mass is defined as the sum of atomic weights of the atoms in the empirical formula. Formula mass is applicable in the case of ionic compounds.

## Example

• Ionic compound like sodium chloride do not contain discrete molecules as their constituent units.
• In such compounds, positive (sodium) and negative (chloride) entities are arranged in a three-dimensional structure.
• The formula such as NaCl is used to calculate the formula mass instead of molecular mass as in the solid state sodium chloride does not exist as a single entity.