How many valence electrons does Chlorine need to GAIN to become stable?

An atom of a group 17 element such as chlorine has seven valence electrons. It is “eager” to gain an extra electron to fill its outer energy level and gain stability. Group 16 elements with six valence electrons are almost as reactive for the same reason

Explanation:

"hydrogen bonding is the attraction of h atoms in the water molecule (slight + charge) to o atoms in a neighboring water molecule (slight - charge); it is a weak interatomic force. but it is still strong enough to the water molecules "stick" together."