Question

I need help with lewis diagram of HCN - which one do I put in the middle?

Answer 1

H-C---N:
Hydrogen forms a single bond with Carbon and carbon a triple bond with nitrogen, with 1 lone pair on the other side of N.

The least electronegative atom is usually the one in the middle, in this case C. You're welcome

Answer 2

The Lewis dot diagram for hydrogen cyanide, `"HCN"`, is `"H:C:::N:"` . There is a single covalent bond between the hydrogen and carbon atom, represented by two dots, `:`, each of which represents a shared electron; a triple covalent bond between the carbon and nitrogen atom, represented by three pairs of dots, `:::`, representing three pairs of shared electrons, and a lone pair of electrons on the nitrogen atom, represented by a pair of dots, `:` .