Magnesium is almost always +2. with an electron configuration of
#1s^2 2s^2 2p^ 3s^2 # Magnesium tends to lose the two 3s electrons. This leaves magnesium with the stable electron configuration of Neon and a positive 2 charge.
Oxygen is almost always -2 with an electron configuration of
# 1s^2 2s^2 2p^4#. Oxygen with a high electro negativity tends to gain to electrons. This leaves Oxygen with the stable electron configuration of Neon and a negatitive 2 charge.
The polyatomic ion of #NO_2# nitrite has a net charge of -1. The charge of the nitrogen can be calculated using the equation.
# 1 xx N + 2 xx O = -1# The charge on Oxygen -2 can be put in for O
# 1 xx N + 2 xx -2 = -1# This gives
# N + -4 = -1# adding +4 from both sides gives
# N + -4 + 4 = -1 + 4# This gives
N = +3
