A polar covalent bond is a type of chemical bond where the sharing of electrons between two atoms is unequal. In other words, one atom exerts a stronger pull on the shared electrons than the other, resulting in an uneven distribution of electron density within the bond.
In a polar covalent bond, the atom with a higher electronegativity (ability to attract electrons) attracts the shared electrons more strongly, developing a partial negative charge (δ-) on that atom. The atom with a lower electronegativity has a partial positive charge (δ+). As a result, the bond has a separation of charges, creating a dipole moment.
The force acting between the two atoms in a polar covalent bond is called an electrostatic force or an electrostatic interaction. This force arises due to the attraction between the partial positive charge on one atom and the partial negative charge on the other atom. It is important to note that the electrostatic force is not as strong as an ionic bond, where complete electron transfer occurs.
The polarity of a covalent bond is determined by the difference in electronegativity between the two atoms. The greater the difference in electronegativity, the more polar the bond becomes. The electronegativity difference can be quantified using various scales, such as the Pauling scale or the Mulliken scale.
Examples of molecules with polar covalent bonds include water (H2O), where oxygen pulls the shared electrons more strongly than hydrogen, resulting in a polar molecule with δ- on oxygen and δ+ on hydrogen. Another example is hydrogen chloride (HCl), where chlorine is more electronegative than hydrogen, leading to a polar covalent bond.