A covalent bond is a type of chemical bond formed between two atoms by sharing electrons. There are two types of covalent bonds: polar and nonpolar.Polar covalent bond:A polar covalent bond occurs when there is a significant difference in electronegativity between the two atoms involved in the bond. Electronegativity is the ability of an atom to attract electrons towards itself. In a polar covalent bond, the electrons are not shared equally between the two atoms, resulting in a partial positive charge on the less electronegative atom and a partial negative charge on the more electronegative atom. This creates a dipole moment, which is a measure of the molecule's overall polarity.Example: In a water molecule H2O , the oxygen atom is more electronegative than the hydrogen atoms. This causes the electrons to be more attracted to the oxygen atom, creating a partial negative charge on the oxygen and partial positive charges on the hydrogen atoms. This results in a polar covalent bond.Nonpolar covalent bond:A nonpolar covalent bond occurs when the electronegativity difference between the two atoms involved in the bond is negligible or very small. In this case, the electrons are shared more or less equally between the two atoms, and there is no significant charge separation or dipole moment.Example: In a hydrogen molecule H2 , both hydrogen atoms have the same electronegativity, so the electrons are shared equally between them. This results in a nonpolar covalent bond.The overall polarity of a molecule depends on the presence and arrangement of polar and nonpolar covalent bonds within the molecule. If a molecule has polar bonds but is symmetrical in shape, the individual bond dipoles may cancel each other out, resulting in a nonpolar molecule. However, if a molecule has polar bonds and an asymmetrical shape, the bond dipoles do not cancel, and the molecule is polar.Examples:1. Carbon dioxide CO2 has polar bonds between the carbon and oxygen atoms, but the molecule is linear and symmetrical, so the bond dipoles cancel each other out, resulting in a nonpolar molecule.2. Ammonia NH3 has polar bonds between the nitrogen and hydrogen atoms, and the molecule has a trigonal pyramidal shape, which is asymmetrical. The bond dipoles do not cancel, resulting in a polar molecule.In summary, the difference between polar and nonpolar covalent bonds lies in the electronegativity difference between the atoms involved in the bond. The presence and arrangement of these bonds within a molecule determine its overall polarity.