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QUESTION

# How can I write the formula for calcium nitride?

"Ca"""_3"N"_2

The correct answer is Ca_3N_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. 1s^22s^22p^63s^23p^64s^2.

It loses two electron in its 4s subshell to achieve stability and forms ion Ca^(2+).

Ca^(2+) = 1s^22s^22p^63s^23p^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) = 1s^22s^22p^3

N^-3 = 1s^22s^22p^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 Ca^(2+) ion and nitrogen atom after gaining three electrons becomes N^(3-) ion.

so in all we have three Ca^(2+) ions and two nitride N^(3-) ions. so the formula becomes Ca_3N_2.