# What is the correct formula for the compound made by magnesium and nitrogen?

Oct 30, 2015

The correct formula for the Magnesium Nitrogen compound is $M {g}_{3} {N}_{2}$.

#### Explanation:

Magnesium has two valence electrons, and Nitrogen has five valence electrons.

Oct 30, 2015

$M {g}_{3} {N}_{2}$, magnesium nitride.

#### Explanation:

Magnesium is in Group 2, nitrogen is in Group 15; the formula is as you would predict from magnesium ion, $M {g}^{2 +}$, and nitride anion, ${N}^{3 -}$. This is an ionic solid that hydrolyzes to give ammonia, and magnesium hydroxide, I.e.:

$M {g}_{3} {N}_{2}$ $+$ $6 {H}_{2} O \rightarrow$$2 N {H}_{3}$ $+$ $3 M g {\left(O H\right)}_{2}$

Oct 30, 2015

Magnesium and nitrogen combine to form magnesium nitride, $\text{Mg"_3"N"_2}$.

#### Explanation:

Magnesium nitride is an ionic compound. Magnesium forms ions with a $\text{2+}$ charge, and nitrogen forms nitride ions with a $\text{3-}$ charge. The overall charge of the compound must be zero. Therefore, the numerical value of the positive and negative charge must be $\text{6}$.

$3 {\left[\text{Mg"]^(2+) + 2 ["N}\right]}^{3 -}$$\rightarrow$$\text{Mg"_3"N"_2}$

$3 \times \left(2 +\right) = 6 +$ and $2 \times \left(3 -\right) = 6 -$

$\left(6 +\right) + \left(6 -\right) = 0$

An easy way to determine the formula unit of an ionic compound is called the crisscross method, as demonstrated in the video below.