Chlorine belongs to Group 7A (or 17) of the periodic table, also called the halogens. Halogens are known for their high electronegativity and reactivity. Chlorine has seven valence electrons, which means that it needs one more electron to achieve a stable electron configuration (like that of a noble gas). Therefore, chlorine can donate one electron.

In chemical reactions, chlorine typically gains one electron to form a chloride ion (Cl-), achieving a complete outer electron shell. This process is known as reduction, where an atom or molecule gains electrons.