# Question #f2b1a

Nov 18, 2016

It's an atom that can have different valencies.

#### Explanation:

Some atoms can have multiple valencies.
Copper is usually $C {u}^{2 +}$, but $C {u}^{+}$ also exists.
Iron can be $F {e}^{2 +}$ or $F {e}^{3 +}$

Chlorine is even 'worse':
It has valencies $- 1 , + 1 , + 3 , + 5 , + 7$ in ions like:
chloride ($C {l}^{-}$), hypochlorite ($C l {O}^{-}$), chlorite ($C l {O}_{2}^{-}$), chlorate ($C l {O}_{3}^{-}$), and perchlorate ($C l {O}_{4}^{-}$).

The above are just examples; there are many more.
In the more elaborate versions of the Periodic System the possible valencies are given.