# What is the formula for rubidium nitride?

Well, $\text{rubidium}$ is an alkali metal.....
...that forms a $R {b}^{+}$ cation....and nitrogen forms a nitride ion....${N}^{3 -}$
$\frac{1}{2} {N}_{2} + 3 {e}^{-} \rightarrow {N}^{3 -}$
....and thus we form a $R {b}_{3} N$ salt when the ions make music together....and this is probably not something we could put into a bottle.....