Hydrogen Cyanide (HCN) is a polar molecule. The polarity of HCN arises due to the difference in electronegativity between the hydrogen (H), carbon (C), and nitrogen (N) atoms.
In HCN, the nitrogen atom is more electronegative than both carbon and hydrogen. This difference in electronegativity causes the nitrogen atom to pull the shared electrons towards itself, creating a partial negative charge (δ-) on the nitrogen and a partial positive charge (δ+) on the hydrogen. The carbon atom, being less electronegative than nitrogen but more electronegative than hydrogen, also contributes to the overall dipole moment of the molecule.
The linear shape of the HCN molecule further enhances its polarity. The dipole moments do not cancel out, resulting in a net dipole moment. Therefore, HCN is a polar molecule.