Question

Somehow the answer to this is (4) but I dont see how that is possible so please EXPLAIN.

Which of the following statements relating to molecular orbital theory (MO) is incorrect?

(1) Combination of two atomic orbitals produces two molecular orbitals

(2) Combination of two 2p orbitals may result in either sigma or pi MOs

(3) A species with a bond order of zero will not be stable.

(4) Molecular orbitals are hybridizations of atomic orbitals.

(5) A diatomic molecule with an odd number of electrons will be paramagnetic

Answer 1

Molecular orbitals are formed due to constructive and destructive interaction of atomic orbitals which is also called the linear combination of atomic orbitals. When atomic orbitals of similar wave function combine, constructive interaction occurs while orbitals with opposite wave function combine destructive interaction occur.

Constructive interaction of atomic orbitals give molecular orbitals of lwer energy called bonding orbital, and in this mlecular orbital the probability that the electron would stay between the nuclei of two atom is maximum.Because the orbitals have lower energy than the corresponding atomic orbitals due to constructive interaction. Hence electrons prefer to stay in these molecular orbitals.

Similarly destructive interaction of atomic orbitals give molecular orbitals of higher energy called anti-bonding orbital, and in this mlecular orbital the probability that the electron would stay between the nuclei of two atom is minimum.. Because the orbitals have higher energy than the corresponding atomic orbitals due to destructive interaction.

However hybridisation is a different concept in which the atomic orbitals are hybridised to give completely different hybridised orbital. The hybridised orbitals have different shape. Here there is no interaction of wave function of atomic orbitals. Hence both molecular orbital and hybrid orbital are different concept. Also molecular orbital explains bonding in molecules in a better way as it considers the wave function of electrons in orbital.

Hence (1) iscorrect and (4) is incorrect.

When two 2p atomic orbitals combine they give either sigma(2P_x),or Pi(2P_y), Pi(2Pz) bonding molecular orbitals and sigmastar(2P_x), or Pistar(2P_y), Pistar(2Pz) antibonding molecular orbitals that depends on the number of electrons present in 2p atomic orbital. Hecnce (2) is correct.

According to molecular orbital theory, a species with a 0 bond order is not stable. It is calculated through the following formulae

Bond order = (Nb - Na)/2 , where Nb = Total number of electrons in all the bonding molecular orbitals.

Na = Total number of electrons in all the anti-bonding molecular orbitals

Hence (3) is correct.

A diatomic molecule with an odd number of electrons will be paramagnetic, because the odd electron will remain unpaired in the molecular orbital. Hence (5) is correct