When does a polar covalent bond form?

Polar covalent bonds form when the constituent atoms have an electronegativity difference between (0.4 and 1.7). It means that the individual atoms have to be either highly electronegative or highly electropositive but not high enough to make the bond so polar that it becomes an ionic bond.

Covalent bonds are the mutual sharing of electrons among two atoms. The reason of this sharing is octet completion which brings stability. These bonds do not depend on electronegativities and electropositivities, but the fact that they can be polar too widens the view of covalent bonds. Polar covalent bonds are actually covalent but they somewhat behave like ionic compounds. This is in terms of the nearness of electron pairs toward one atom and far from the other. This does happen in polar covalent bonds but to a limited extent.

Ionic bonds are in fact highly polar covalent bonds. So a little less polar covalent bonds are termed just polar covalent bonds.

Electronegative elements bonded to hydrogen atoms usually show polar covalent bonds because the difference among their electronegativities is not enough to reach the ionic limit i.e. (above 1.7). So the hydrogen bond is also included in polar covalent bonds if being studied in intramolecular forces.

Difference between covalent and ionic bonds

The difference between ionic, polar covalent, and non-polar covalent bonds is well explained by the following table.

So, the electronegativity difference of (0.4) to (1.7) makes a bond polar covalent.

Examples of polar covalent bonds

Bonds can be pretty confusing in terms of polarity. Some examples are listed below which have been picked based on the electronegativity differences these molecules have.

1. Hydrogen fluoride (HF)
2. Hydrogen chloride (HCl)
3. Hydrogen bromide (HBr)
4. Hydrogen iodide (HI)
5. Hydrogen selenide (H₂Se)
6. Ammonia (NH₃)
7. Sulphur dioxide (SO₂)
8. Water (H₂O)
9. Hydrogen sulphide (H₂S)
10. Methanol (CH₃OH), etc.

All of the above listed compounds have an electronegativity difference of more than 0.4 but less than 1.7.

You might want to check out a related covalent bond that isn’t pure covalent too.