A nitride ion has 7 protons, 8 neutrons, and 10 electrons. What is the overall charge on this ion?
The net charge of an ion is given by the balance that exists between the number of protons present in the nucleus and the number of electrons that surround the nucleus.
Neutrons play no role in the net charge of an atom, so you can ignore them here.
When an atom has equal numbers of protons and electrons, its net charge is equal to zero, i.e. it is a neutral atom.
In your case, the nitride ion is said to have
- seven protons in its nucleus
- ten electrons surrounding its nucleus
The neutral atom would have contained
The magnitude of the negative charge is given by the difference between the number of protons and the number of electrons. In this case, each extra electron will add a charge of
You will thus have
#3 color(red)(cancel(color(black)("extra e"^(-)))) * ((1-)color(white)(a)"charge")/(1color(red)(cancel(color(black)("extra e"^(-))))) = (3-)color(white)(a)"charge"#
Therefore, the overall charge on the nitride anion is
#"N"^(3-) ->#the nitride anion