9 electrons when there is no charge shown. It has 2 shells, this is easy to see on the periodic table because it is in the second row. Otherwise you can count. There is 2 electrons on the inner shell then every shell after holds 8. Fluorine only has 9 electrons so 2 for the first shell and 7 on the outter shell. It needs 1 more electron to fill its outter (valence) shell.
