Here's why:

* Lewis Structure: Chlorine has 7 valence electrons. In Cl₂, each chlorine atom shares one electron with the other, forming a single covalent bond. This results in both chlorine atoms having a complete octet.

* VSEPR Theory: The Valence Shell Electron Pair Repulsion (VSEPR) theory predicts the shape of molecules based on the repulsion between electron pairs around the central atom. In Cl₂, there are no lone pairs of electrons on either chlorine atom, only the shared pair in the bond.

* Linear Geometry: With two atoms and no lone pairs, the only possible arrangement is a straight line, resulting in a linear molecular geometry.