Question

1. Construct a molecular orbital diagram that describes the cyanide ion, CN Your diagram should be labeled to show the individual σ and π molecular orbitals, and the HOMO and the LUMO

Answer 1

(LUHD) 唧 (HOMO) of Carborn Ener

Molecular orbitals are formed by linear combination of atomic orbitals. In CN^{​​​​​-} ​​, valence shell electrons of carbon are 4 and nitrogen has 5 electrons

C (6) : 1s² 2s² 2p²

N (7): 1s² 2s² 2p³

Total valence electrons =

4 (of carbon)+ 5 (of nitrogen) + one - charge

= 10 electrons

As nitrogen is more electronegative than carbon, so orbitals of nitrogen are lower in energy, that's why we put the electron of - charge in nitrogen orbital.

HOMO: 3 sigma ( bonding mo)

LUMO: two 1π^* ( I.e. antibonding mos)