Question

Find out the number of valence electrons in : (a) Sodium ion (b) Chloride ion

Answer 1

Valence electron:

1. The outermost electron shell of an atom is called the valence shell.
2. The electrons present in the outermost electron shell of an atom are called valence electrons.

(a) Valence electrons in Sodium ion $\left({\mathrm{Na}}^{+}\right)$:

1. Sodium $\mathbf{\left(}\mathbf{Na}\mathbf{\right)}$ has atomic number $11$.
2. The electronic configuration of Sodium is $(2,8,1)$.
3. Sodium atom $\mathbf{\left(}\mathbf{Na}\mathbf{\right)}$ loses one electron from the outermost shell and forms a Sodium ion $\left({\mathrm{Na}}^{+}\right)$.
4. Thus, the electronic configuration of Sodium ion is $(2,8)$.
5. The outermost shell of Sodium ion has $8$ electrons.

Thus, the number of valence electrons in Sodium ion are $8$.

(b) Valence electrons Chloride ion $\left({\mathrm{Cl}}^{-}\right)$:

1. Chlorine $\mathbf{\left(}\mathbf{Cl}\mathbf{\right)}$ has atomic number $17$.
2. The electronic configuration of Chlorine is $(2,8,7)$.
3. Chlorine atom $\mathbf{\left(}\mathbf{Cl}\mathbf{\right)}$ gains one electron in the outermost shell and forms a Chloride ion $\left({\mathrm{Cl}}^{-}\right)$.
4. Thus, the electronic configuration of Chloride ion is $(2,8,8)$.
5. The outermost shell of Chloride ion has $8$ electrons.

Thus, the number of valence electrons in Chloride ion are $8$.