Answer:
Group number − 18 = ion charge
Explanation:
Negatively charged ions can be found in groups 15, 16, and 17.
Nitrogen and phosphorous are group 15 elements and have an ion charge of -3.
Oxygen and silicon are group 16 elements and have an ion charge of -2.
Fluorine, chlorine, bromine, and iodine are group 17 elements and have an ion charge of -1.
Thus, the group number minus 18 equals the negative ion charge.
