Magnesium (group IIA) loses two electrons to become a cation. This is the most energetically favorable way for Magnesium to obtain a valence electron that is stable (octet). When an atom loses electrons it has a positive charge that matches the number of electrons lost.
Nitrogen (group VA) gains three electrons to become an anion. This is the most energetically favorable way for Nitrogen to obtain a valence electron that is stable (octet). When an atom gains electrons it has a negative charge that matches the number of electrons gained.
According to Kinetic Molecular Theory, an increase in temperature will increase the average kinetic energy of the molecules. As the particles move faster, they will likely hit the edge of the container more often.
