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The elements belonging to the seventeenth group (7A) are called halogens. Due to high nuclear attraction, these elements have smallest atomic radius in the respective periods. They are also the most electronegative elements in the respective periods. The distinguishing electron enters the p-orbital.

The general outer electronic configuration of a halogen is given by$n{s}^2 n{p}^5$ . Therefore, it contains 7 electrons in the valence shell and requires one more electron to complete its octet.

Halogens form monovalent anions by accepting an electron. These ions have the electronic configuration $n{s}^2 n{p}^6$ , which is the electronic configuration of noble gases with a complete octet.

Chlorine can complete its octet by forming ionic or covalent bonds.

Chorine forms ionic bonds with alkali metals. Alkali metals are elements belonging to group 1 and have one electron in the valence shell. These elements remove the one excess electron to obtain a stable configuration, thus forming a monovalent cation. The electron removed from alkali metal is accepted by chlorine to form a monovalent anion. The anion and cation are held by electrostatic forces forming an ionic bond.

These compounds include sodium chloride (NaCl), potassium chloride (KCl), etc.

Chorine forms a covalent bond with other electronegative atoms. It can also form a covalent bond with another chlorine atom. During the formation of a covalent bond, the valence electrons are shared between atoms to obtain stable electronic configurations. The unpaired electron in the valence shell of chlorine is used for sharing.

Compounds such as chlorine gas ($C{l}_2$) and carbon tetrachloride ($CC{l}_4$) contain chlorine with a covalent bond.