Chemistry Class 11 NCERT Solutions: Chapter 4 Chemical Bonding and Molecular Structure Part 6

Q:27. Draw diagrams showing the formation of a double bond and a triple bond between carbon atom in Equation and Equation molecules.

Answer:

The electronic configuration of Equation in the excited state is:

Equation

In the formation of an ethane molecule Equation , one Equation hybrid orbital of carbon overlaps a Equation hybridized orbital of another carbon atom, thereby forming a C-C sigma bond. The remaining two Equation orbitals of each carbon atom form a Equation sigma bond with two hydrogen atoms. The unhybridized orbital of one carbon atom undergoes sidewise overlap with the orbital of a similar kind present on another carbon atom to form a weak n-bond.

(A)

(B)

(C)

(D) figure:

Equation

In the formation of Equation molecule, each C-atom is sp hybridized with two 2p-orbitals in an unhybridized state. One sp orbital of each carbon atom overlaps with the other along the internuclear axis forming a c- c sigma bond. The second sp orbital of each C-atom overlaps a half- filled 1s-Orbital to form a Equation bond.

The two unhybridized 2p-orbitals of the first carbon undergo sidewise overlap with the 2p orbital of another carbon atom, thereby two carbon atoms is made up of one sigma and two n-bonds.

(A)

(B)

(C)

Q: 28. What is the total number of sigma and pi bonds in the following molecules?

(A) Equation

(B) Equation

Answer:

A single bond is a result of the axial overlap of bonding orbitals. Hence, it contributes a sigma bond. A multiple bond (double or triple bond) is always formed as a result of the sidewise overlap of orbitals. A pi-bond is always present in it. A triple bond is a combination of two pi-bonds and one sigma bond.

Structure of Equation can be represented as:

Equation

Hence, there are three sigma and two pi-bonds in Equation

The structure of Equation can be represented as:

Figure:

Hence, there are five sigma bonds and one pi-bond in Equation

Q: 29. Considering x-axis as the internuclear axis which out of the following will not form a sigma bond and why?

(A) Equation

(B) Equation

(c) Equation

(D) Equation

Answer:

Equation orbitals will not a form a sigma bond. Taking X-axis as the internuclear axis,

Equation orbitals will undergo lateral overlapping, thereby forming a pi Equation bond.

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