Covalent bonds with a large difference in electronegativity between the bonded atoms are the most polar. Electronegativity is the ability of an atom to attract electrons towards itself. When there is a large difference in electronegativity between two atoms, the more electronegative atom will attract the electrons in the bond more strongly, creating a partial negative charge on itself and a partial positive charge on the less electronegative atom. This creates a polar covalent bond.

Some examples of highly polar covalent bonds include:

- Hydrogen-fluorine bond (H-F)

- Hydrogen-oxygen bond (H-O)

- Hydrogen-nitrogen bond (H-N)

- Chlorine-fluorine bond (Cl-F)

- Bromine-fluorine bond (Br-F)

The polarity of a covalent bond can have a significant impact on the properties of a compound. For example, polar covalent bonds can contribute to the formation of hydrogen bonds, which are strong intermolecular forces that can affect the boiling point, melting point, and solubility of a compound.