# How can I write the formula for calcium nitride?

Jul 3, 2014

${\text{Ca"""_3"N}}_{2}$

#### Explanation:

The correct answer is $C {a}_{3} {N}_{2}$.

Let us see how we got the answer; Look at the electronic arrangement of Ca and N atom.

Ca ( Z= 20) has 20 electrons with following electronic configuration. 1${s}^{2}$2${s}^{2}$2${p}^{6}$3${s}^{2}$3${p}^{6}$4${s}^{2}$.

It loses two electron in its 4s subshell to achieve stability and forms ion $C {a}^{2 +}$.

$C {a}^{2 +}$ = 1${s}^{2}$2${s}^{2}$2${p}^{6}$3${s}^{2}$3${p}^{6}$

N ( Z=7) on the other hand has seven electrons and wants to gain three electrons to achieve stable noble gas configuration.Nitrogen atom on gaining three electrons forms negative nitride ion, ${N}^{3 -}$ ion.

N ( Z=7) = 1${s}^{2}$2${s}^{2}$2${p}^{3}$

${N}^{-} 3$ = 1${s}^{2}$2${s}^{2}$2${p}^{6}$

Two Nitrogen atoms gains three electrons each ( total of six) from three Ca atoms, each Ca atom loses two electrons (total of six) to two Nitrogen atom , in this process each Ca atom becomes $C {a}^{2 +}$ ion and nitrogen atom after gaining three electrons becomes ${N}^{3 -}$ ion. so in all we have three $C {a}^{2 +}$ ions and two nitride ${N}^{3 -}$ ions.
so the formula becomes $C {a}_{3} {N}_{2}$.