Fluorine has seven electrons in its outer energy level. According to the octet rule, it wants to take on another electron.
Explanation;
-The octet rule refers to the tendency of atoms to prefer to have eight electrons in the valence shell. When atoms have fewer than eight electrons, they tend to react and form more stable compounds.
-Therefore, fluorine which has seven electrons requires to gain one electron to have eight electrons in the outermost energy level, making it stable (octet). In other words fluorine reacts by gaining one electron.
