# What is the difference between molecular mass and formula unit mass?

• Formula unit masses are used to describe ionic compounds, i.e. ionically-bonded compounds found as lattice structures. One formula unit of sodium chloride, $\text{NaCl}$, is found in...
It makes no physical sense to prescribe a molecular mass to $\text{NaCl}$, nor does it make physical sense to designate ${\text{CO}}_{2}$ as a formula unit.