Charge number

Charge number is the coefficient that, when multiplied by the elementary charge, gives the charge of an ion.

For example, the charge on a Chloride ion, $$\mathrm{Cl}^-$$, is $$-1 \cdot q$$, where q is the elementary charge. This means the charge number for the ion is $$-1$$.

$$z$$ is sometimes used as the symbol for the charge number. In that case, the charge of an ion could be written as $$z q$$.