Give the name and formula of the compound formed from the following elements: (a) sodium and nitrogen; (b) oxygen and strontium; (c) aluminium and chlorine

Electronic configuration of sodium :$\left[\mathrm{Ne}\right]\mathbf{3}{\mathbf{s}}^{\mathbf{1}}$

Sodium is an electropositive element, by losing 1 electron it will be converted into${\mathbf{Na}}^{\mathbf{+}}$ .

Electronic configuration of nitrogen :$\left[\mathrm{He}\right]\mathbf{2}{\mathbf{s}}^{\mathbf{2}}\mathbf{2}{\mathbf{p}}^{\mathbf{3}}$

Nitrogen is an electronegative element. It will gain three electrons to form${\mathbf{N}}^{\mathbf{3}\mathbf{-}}$ .

Now, by the criss-cross method, the oxidation state of the ions gets exchanged and they form the subscripts of each other. This results in the formation of a neutral compound.

So, the chemical formula for sodium nitrite is${\mathbf{Na}}_{\mathbf{3}}\mathbf{N}$ .

Electronic configuration of aluminium :$\left[\mathrm{Ne}\right]\mathbf{3}{\mathbf{s}}^{\mathbf{2}}\mathbf{3}{\mathbf{p}}^{\mathbf{1}}$

Aluminium is an electropositive element, by losing three electrons it will be converted into ${\mathbf{AI}}^{\mathbf{3}\mathbf{+}}$.

Electronic configuration of chlorine :$\left[\mathrm{Ne}\right]\mathbf{3}{\mathbf{s}}^{\mathbf{2}}\mathbf{3}{\mathbf{p}}^{\mathbf{1}}$

Chlorine is an electronegative element. It will gain one electron to form ${\mathbf{CI}}^{\mathbf{-}}$.

Now, by the criss-cross method, the oxidation state of the ions gets exchanged and they form the subscripts of each other. This results in the formation of a neutral compound.

So, the chemical formula for aluminium chloride is ${\mathbf{AICI}}_{\mathbf{3}}$.