[submar1ney]

Hi.

I have an empirical formula for Magnesium Nitride as Mg3N2. I understand that valency of an element is the number of atoms that will combine with another element, ie 3 nitrogen atoms combine with 2 magnesium atoms, but why do the number swap over in the empirical formula?

Cheers

[Kryolith]

Mg is in the 2nd main group. It has the tendency to donate 2 electrons.
N is in the 5th main group. It has the tendency to accept 3 electrons.

So how will these elements combine?