Describe hybridisation in the case of PCl₅ and SF₆. The axial bonds are longer as compared to equatorial bonds in PCl₅ whereas in SF₆ both axial bonds and equatorial bonds have the same bond length. Explain.

Use the molecular orbital energy level diagram to show that N2 would be expected to have a triple bond, F2, a single bond and Ne2, no bond.

Briefly describe the valence bond theory of covalent bond formation by taking an example of hydrogen. How can you interpret energy changes taking place in the formation of dihydrogen?

(i)Discuss the concept of hybridization. What are its different types in a carbon atom?

(ii) What is the type of hybridisation of carbon atoms marked with star.

Comprehension given below is followed by some multiple choice questions. Each question has one correct option. Choose the correct option.

Molecular orbitals are formed by the overlap of atomic orbitals. Two atomic orbitals combine to form two molecular orbitals called bonding molecular orbital (BMO) and anti bonding molecular orbital (ABMO). Energy of anti bonding orbital is raised above the parent atomic orbitals that have combined and the energy of the bonding orbital is lowered than the parent atomic orbitals. Energies of various molecular orbitals for elements hydrogen to nitrogen increase in the order :

σσ < σ *1s < σ2s < (π2p_x = π2p_y) < σ2p₂ < σ2p_z < (π * 2p_x = π*2p_y) < σ* 2p_z s ( p p) p ( * p * p) * p < and for oxygen and fluorine order of energy of molecular orbitals is given below :

σls < σ* 1s < σ2s < σ* 2s < σ2p_z < (π2p_x = π2p_y) < (π* 2p_x = π * 2p_y) < σ* 2p_z

Different atomic orbitals of one atom combine with those atomic orbitals of the second atom which have comparable energies and proper orientation. Further, if the overlapping is head on, the molecular orbital is called ‘Sigma’, (σ) and if the overlap is lateral, the molecular orbital is called ‘pi’, (π). The molecular orbitals are filled with electrons according to the same rules as followed for filling of atomic orbitals. However, the order for filling is not the same for all molecules or their ions. Bond order is one of the most important parameters to compare the strength of bonds.

Which of the following statements is correct?

(i) In the formation of dioxygen from oxygen atoms 10 molecular orbitals will be formed.

(ii) All the molecular orbitals in the dioxygen will be completely filled.

(iii) Total number of bonding molecular orbitals will not be same as total number of anti bonding orbitals in dioxygen.

(iv) Number of filled bonding orbitals will be same as number of filled anti bonding orbitals