If the ion is named by (element-name) + ion, it is the element with a positive charge.
This means:
Sodium ion: Na(1+)
Aluminum ion: Al(3+)
If the ion is named by (element-prefix)+ide, then it has a negative charge.
This means:
Chloride: Cl(1-)
Nitride: N(3-)
Finally, if it has roman numerals after the name, that is the amount of positive charge the ion has.
Therefore:
Iron (II): Fe(2+)
Iron(III): Fe(3+)
