How many electrons does fluorine have? How many electron shells? How many electrons are needed to fill the valence shell?

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.

Explanation:

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6