Question

How can I write the formula for potassium nitride?

Answer 1

The correct answer is `K_3N`.

To see how we arrived at that answer, we first have to examine the electronic configuration of `K` and `N`.

`K` has `19` electrons and has the following electronic configuration `rarr 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1`

As potassium obeys the octet rule, it will lose one electron in its `4s` subshell to achieve a stable octet noble gas configuration, forming the ion, `K^+`.

Electronic configuration of `K^+ rarr 1s^2 2s^2 2p^6 3s^2 3p^6`

`N` has seven electrons and has the following electronic configuration `rarr1s^2 2s^2 2p^3`

Nitrogen also obeys the octet rule and will gain three electrons to achieve stable octet noble gas configuration, forming the negative nitride ion, `N^-3`.

Electronic configuration of `N^-3rarr1s^2 2s^2 2p^6`

Each nitrogen atom gains three electrons from three potassium atoms and each potassium atom loses one electron to a nitrogen atom. In this process each potassium atom becomes `K^+` ion and each nitrogen atom `N^-3` ion.

The first 1:30 of this video shows the movement of the electrons in potassium nitride (wordlessly).