Chapter 4: Chemical Bonding and Molecular Structure

Electronic configuration of C- atom:

6C :

The orbital picture of C- atom in excited state is:

Thus, C- atom undergoes sp³ hybridization in methane molecule and forms a tetrahedral structure.

For square planer geometry, C-atom should have dsp² hybridization. But as C- atom does not have a d- orbital, it cannot undergo dsp² hybridization. Thus, Methane’s geometry cannot be square planer.

Also in square planar geometry the bond angle is

Lewis structure of BeH₂ is:

Central atom is not having any lone pair but has 2 bond pairs. Thus, its shape is AB₂, i.e., linear shape.

Thus, the dipole moment of Be- H bond is equal and opposite in direction, nullifying one another. Thus, the dipole moment of BeH₂ is 0.

N- atom is the central atom of NF₃ and NH₃.

Central atom has 1 lone pair and is having 3 bond pairs. Thus,  for both, the shape is AB₃E, i.e., pyramidal.

As, the F-atom has more electronegativity than the H- atom, NF₃ should have a higher dipole moment than NH₃. But the dipole moment of NH₃ is 1.46D which is higher than the dipole moment of NF_3, which is 0.24D.

It gets clear from the directions of dipole moments of individual bonds in NF₃ and NH₃.

As both the N-H bonds are in the same direction, it adds to the bond moment of the lone pair, while N-F bonds are in the opposite direction. So they partly cut the bond moment of lone pair.

Thus, dipole moment of NH₃ is higher than that of NF₃.

“Hybridization is defined as an intermixing of a set of atomic orbitals of slightly different energies, thereby forming a new set of orbitals having equivalent energies and shapes”.

E.g. 1 s- orbital hybridises with 3 p- orbitals to form 4 sp³ hybrid orbitals.

(a) sp hybrid orbital

1 s- orbital hybridises with 1 p- orbitals to form 2 sp hybrid orbitals. sp hybrid orbital has a linear shape. The formation of sp orbital is:

(b) sp² hybrid orbital

1 s- orbital hybridises with 2 p- orbitals to form 3 sp² hybrid orbitals. The shape of sp² orbital is trigonal planar.

(c) sp³ hybrid orbital

1 s- orbital hybridises with 3 p- orbitals to form 4 sp³ hybrid orbitals. The shape of sp³ orbital is a tetrahedron.

The ground state of the valence orbital of Al –atom is:

In excited state the orbital picture of Al- atom is:

Thus, Al -atom in AlCl₃ undergoes sp² hybridisation and forms trigonal planar geometry. For the formation of

N- atom in NH₃ has sp3 hybridization. The orbital picture of N- atom is shown below:

B- atom in NF₃ has sp2 hybridisation . The orbital picture of B- atom is shown below:

On the reaction of NH3 and BF₃, F₃B.NH₃ is obtained as a product, as hybridization of B-atom is changed to sp³. Although, hybridization of N- atoms remain unchanged.

C₂H₄

The electronic configuration of a carbon atom in excited state is given below:

₆C:

In the formation of C₂H₄ (ethane) molecule 1 sp² orbital of the C- atom overlaps sp² orbital of the other C- atom, thus forming a C-C sigma bond.

The 2 remaining sp² orbitals of every C- atom forms sp²-s

C₂H₂

In the formation of the ethyne(C₂H₂) molecule, C- atom has sp hybridization with 2 2p- orbitals in an unhybridized state.

1 sp orbital of each C- atom overlaps the inter-nuclear axis and forms C-C sigma bond. The 2^ndsp orbital of each C- atom overlaps half-filled 1s orbital so as to form a sigma bond.

The triple bond between the 2 C- atoms has 1 sigma bond and 2 Pie bonds. This is because 2 unhybridized 2p- orbitals overlap with the 2p- orbital of other C- atom, thus forming 2 pie bonds.

A single bond is formed as the axis of bonding orbital overlaps. Thus, it forms a

(a) C₂H₂

Thus, there are 2

(b) C₂H₄

Thus, there are 1

(c) 2p_y and 2p_y

2p_y and 2p_y orbitals won’t form a

(a) CH₃-CH₃

Here, C₁ and C₂ have sp³ hybridization.

(b) CH₃-CH=CH₂

Here, C₃ and C₂ have sp² hybridization and C₁ has sp³ hybridization.

(c) CH₃-CH₂-OH

Here, C₁ and C₂ have sp³ hybridization.

(d) CH₃-CHO

Here, C₁ has sp³ hybridization and C₂ has sp² hybridization.

(e) CH₃COOH

Here, C₁ has sp³ hybridization and C₂ has sp² hybridization.