Question

Define the formula mass of ionic compounds.

Answer 1

Definition of formula mass of ionic compounds:

1. The sum of atomic masses of all the atoms in the ions of an ionic compound is known as its formula mass.

Example:

1. Sodium chloride $\mathbf{\left(}\mathbf{NaCl}\mathbf{\right)}$ is an ionic compound.
2. It contains one sodium ion $\mathbf{\left(}{\mathbf{Na}}^{\mathbf{+}}\mathbf{\right)}$ and one chloride ion $\mathbf{\left(}{\mathbf{Cl}}^{\mathbf{-}}\mathbf{\right)}$.
3. Thus, the formula mass of Sodium chloride is the sum of atomic masses of sodium $\left(23u\right)$ and chlorine $(35.5u)$.
4. Thus, the formula mass of Sodium chloride is $(23+35.5)u$ = $58.5u$