# How can I write the formula for potassium nitride?

Jul 2, 2014

The correct answer is ${K}_{3} N$.

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 $\rightarrow 1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 4 {s}^{1}$

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

Electronic configuration of ${K}^{+} \rightarrow 1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6}$

$N$ has seven electrons and has the following electronic configuration $\rightarrow 1 {s}^{2} 2 {s}^{2} 2 {p}^{3}$

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

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).