The polar covalent bonds are formed when the electronegativities of the atoms are different: the most electronegative atoms will pull the electrons with more strength, yielding a partial negative charge over the most electronegative atom and a partial positive charge over the least electronegative atom.
Explanation:
Covalent bond is the chemical bond where the electrons are shared.
A polar covalent bond is the covalent bond formed when the electrons are not shared equally.
Electronegativity is the relative attraction with which the atoms of an element attract the electrons in a covalent bond. The higher the electronegativity the higher the ability of the atoms to attract the electrons.
Thus, electronegativities are directly responsible for the polar character of the bonds: if the two atoms that form the polar bond have high electronegativity difference, then the most electronegative atom will pull the electrons with more strength, causing a partial negative charge over the most electronegative atom and a partial positive charge over the least electronegative atom. This is a polar covalent bond.
For example, fluoride, F, is the element with the highest electronegativiy (3.98). Hydrogen has electronegativy 2.2. So The bonds H - F, with electronegativity difference 3.98 - 2.2 = 1.78 are polar covalent bonds because F attracts the electrons more strongly than H does.
