Here's why:

* Sodium (Na) is a metal in group 1 of the periodic table, meaning it has a +1 charge as an ion (Na+).

* Fluorine (F) is a nonmetal in group 17 of the periodic table, meaning it has a -1 charge as an ion (F-).

To form a neutral compound, one sodium ion (Na+) combines with one fluoride ion (F-). This results in the ionic compound sodium fluoride (NaF).