Charge number

Charge number or just valance of an ion is the coefficient that, when multiplied by the elementary charge, gives the ion's charge.

For example, the charge on a chloride ion, $\mathrm{Cl}^-$, is $-1 \cdot e$, where e 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 $Q = z e$.

For an atomic nucleus, which can be regarded as an ion having stripped off all electrons, the charge number is identical with the atomic number Z (number of protons).

In particle physics the charge number is a (derived) flavour quantum number, mostly denoted by Q (regarded as 'electric charge in units of e') rather than z. For color charged particles with like quarks and hypothetical leptoquarks the charge number is a broken multiple of 1/3.

See also

• Mass-to-charge ratio
• Atomic number