Formula Writing Chemistry Example 4

Solution

1. 1
   Check the student's formula: $\text{MgN}$ would have charges $+2 + (-3) = -1$, which is not neutral. Ionic compound formulas must have zero net charge.
2. 2
   Using the crisscross method: $\text{Mg}^{2+}$ and $\text{N}^{3-}$ → $\text{Mg}_3\text{N}_2$. Verify: $3(+2) + 2(-3) = +6 - 6 = 0$.
3. 3
   The correct formula is $\text{Mg}_3\text{N}_2$ — three magnesium ions balance two nitride ions.