The bond pair of electrons are not shared equally when two unique atoms with different electronegativities join to form a covalent bond. The bond pair is attracted to the nucleus of an atom with a higher electro-negativity. As a result, the electron distribution is distorted, and the electron cloud is attracted to an electronegativity atom.
As a result, the electronegative element becomes slightly negatively charged, while the positively charged atom becomes slightly positively charged. As a result, a molecule develops two opposite poles, and the type of bond formed is known as a ‘polar covalent bond.’
For example, HCl has a polar covalent bond. The Cl- atom in HCl has a higher electronegativity than the H- atom. As a result, the bond pair shifts towards the Cl- atom and gains a positive charge.