Q.Formula mass with an example.

Step 1. Some substances, most notably ionic solids like sodium chloride, do not exist as discrete, isolated molecules — instead their ions are arranged in a continuous repeating 3-D lattice (each Na+ surrounded by six Cl- ions, and vice versa).

Step 2. Because there is no true 'molecule' to weigh, the term 'formula mass' is used instead of 'molecular mass': it is the sum of the atomic masses of all the atoms shown in the compound's representative formula. …

Explain why formula mass replaces molecular mass for lattice/ionic compounds, and demonstrate …

• Using the term 'molecular mass' interchangeably for NaCl without explaining why that term is technically …