Show the formation of aluminium ion.( Atomic number of aluminium = 13).

Definition of valency.

The number of valence electrons lost or gained by an atom in order to attain stability is called valency.

The atomic number of aluminium = 13

Electronic configuration = 2,8,3

since aluminium has three electron in its outermost shell, it does not have stable electronic configuration.

Aluminium loses its three electrons and achieve the stable configuration as 2,8.

$$\begin{gathered} \mathrm{Al}-3{\mathrm{e}}^{-}\to {\mathrm{Al}}^{3+} \\ 2,8,32,8 \end{gathered}$$

An aluminium atom($\mathrm{Al}$) has 13 protons and 13 electrons. On losing one electron, it becomes an aluminium ion(${\mathrm{Al}}^{3+}$).