According to the octet rule, atoms generally form bonds to achieve a stable configuration of eight electrons in their valence shell . However, there are several exceptions to this rule . One such exception is the incomplete octet of the central atom, which is characteristic of electron-deficient compounds . In $BCl_{3}$, the central boron atom has three valence electrons and forms three covalent bonds with chlorine atoms. This results in a total of only six electrons surrounding the boron atom . Since this is fewer than the eight electrons required for an octet, $BCl_{3}$ is electron deficient. In contrast, $CCl_{4}$ follows the octet rule with eight electrons, and $PCl_{5}$ represents an 'expanded octet' with ten electrons .