Question

Write the balanced chemical equations for the reaction of magnesium metal with oxygen gas, and for the reaction of magnesium metal with nitrogen gas

Answer 1

Magnesium element exists as single atoms. Free oxygen is always diatomic (two atoms bonded together) as O2. Nitrogen gas is also diatomic N2.

2Mg + O2 → MgO

Mg forms a +2 ion, O forms a -2 ion, so they combine and balance in a 1:1 ratio. MgO, magnesium oxide, is a solid. 
3Mg + N2→Mg3N2

Mg forms a +2 ion, but N forms a -3 ion. Hence the Mg3N2 configuration for magnesium nitride.