Why is HCN is a dipole-dipole compound?

Answer 1

HCN is a linear molecule and as nitrogen is the most electronegative atom a small negative charge builds on the nitrogen atom and a small positive charge on the hydrogen. This forms a dipole (dipole means two oppositely charged ends). The intermolecular forces between HCN molecules are electrostatic and are caused by the dipole on one molecule interacting with one on another molecule. This is called dipole -dipole interaction.