Define formula mass of a compound.

Part 1: Definition of formula mass of a compound:

• The sum of atomic masses of all the atoms present in a molecule of an ionic compound is known as the formula mass of a compound.
• This is generally used for ionic compounds which do not contain discrete molecules, but ions as their constituent units.

Part 2: Example of formula mass:

The formula mass of Calcium chloride $\mathbf{\left(}{\mathbf{CaCl}}_{\mathbf{2}}\mathbf{\right)}$:

• ${\mathrm{CaCl}}_2$ contains one Calcium $\mathbf{\left(}\mathbf{Ca}\mathbf{\right)}$ and two Chlorine $\mathbf{\left(}\mathbf{Cl}\mathbf{\right)}$ atoms.
• The formula mass of ${\mathrm{CaCl}}_2$ = ($1\times$Atomic mass of Calcium) $+$ ($2\times$Atomic mass of Chlorine)
• The formula mass of ${\mathrm{CaCl}}_2$ = $(1\times 40)+(2\times 35.5)\mathrm{u}$
• Thus, the formula mass of ${\mathrm{CaCl}}_2$ = $111\mathrm{u}$