# What are the formulas for the following ionic compounds: sodium sulphide, caesium bromide and magnesium nitride?

Apr 1, 2018

$\text{Sodium sulfide}$...sodium is a Group 1 metal, and thus has one valence electron to lose to give the $N {a}^{+}$ ion. On the other hand, sulfur is a Group 16 atom, that is likely to pick up two electrons to form the ${S}^{2 -}$...and thus we got $N {a}_{2} S$..
$\text{Caesium bromide}$...caesium is a Group 1 metal, and thus has one valence electron to lose to give the $C {s}^{+}$ ion. On the other hand, bromine is a Group 17 atom, that is likely to pick up ONE electrons to form the $B {r}^{-}$...and thus we got $C s B r$..
$\text{Magnesium nitride}$...magnesium is a Group 2 metal, and thus has two valence electron to lose to give the $M {g}^{2 +}$ ion. Nitride anion is ${N}^{3 -}$...i.e. it picks up THREE electrons to fill its valence shell...and so again the salt is electrically neutral, i.e. $M {g}_{3} {N}_{2}$.