What charge does nitrogen have?
Elemental nitrogen has no charge.
In ammonia (NH3) and ammonium ions (NH4+) it has a oxidation value of -3 (and actually only a partial negative charge as part from a polar covalent, non-ionic bond).
In Nitrate (NO3-) its oxidation value is +5, in nitrite +3 (but only a partial positve charge in both)
The formula for magnesium nitride is Mg3N2, so there are two nitrogen atoms present in a single molecule of magnesium nitride. In this case, the magnesium has a +2 charge, and the nitrogen has a -3 charge, which accounts for why more than one of each must come together and form a molecule (the total charge needs to be zero).
That depends on if the nitrogen ion is bonded with anything else. If it is a plain nitrogen ion it is called Nitride and has a charge of minus 3. If it is bonded with oxygen it is called Nitrate ion, NO4 (charge of minus 2) Nitrogen can also bond with hydrogen, in which case it can either take the form of the NH4 (+1) ion which is called Ammonium or the Amide ion which…
The nitride ion is N3-, three nitrogen atoms bound by three extra electrons to form one molecule of nitrogen. http://en.wikipedia.org/wiki/Nitride The nitrite ion is NO2-. One nitrogen atom with two oxygen atoms that share an electron to form a molecule of nitrogen dioxide. http://en.wikipedia.org/wiki/Nitrite The nitrate ion is NO32-. The nitrate ion carries a formal charge of negative two, where each oxygen carries a −2/3 charge while the nitrogen carries a +1 charge. http://en.wikipedia.org/wiki/Nitrate
There is no specific charge on the nitrogen atom as it is part of a polyatomic ion, NH4+. However, if you want to work through the advanced inorganic chemistry fun, nitrogen and hydrogen have electronegativity values of 3.04 and 2.20 respectively. If you work out the bond angles and remember that you are already one electron short of a happy molecule, you can figure out the dipole moment of the nitrogen atom.