Chemistry Class 11 NCERT Solutions: Chapter 4 Chemical Bonding and Molecular Structure Part 9

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Q: 39. Define hydrogen bond. Is it weaker or stronger than the van der Waals forces?

Answer:

A hydrogen bond is defined as an attractive force acting between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule (may be of the same kind).

Due to a difference between electronegativities, the bond pair between hydrogen and the electronegative atom gets drifted far away from the hydrogen atom. As a result, a hydrogen atom becomes electropositive with respect with respect to the other atom and acquires a positive charge .

The magnitude of H-Bonding is maximum in the solid state and minimum in the gaseous state.

There are two types of H-bonds:

(i) Intermolecular H-bond e.g., HF, etc

(ii) Intramolecular H-bond e.g., o-nitrophenol

Hydrogen bond are stronger than Van der Walls forces since hydrogen bond are regarded as an extreme form of dipole-dipole interaction.

Q: 40. What is meant by the bond order? Calculate the bond order of:

Answer: Bond order is defined as one-half of the difference between the number of electrons present in the bonding and anti-bonding orbitals of a molecule.

If is equal to the number of electrons in an anti-bonding orbital, then is equal to the number of electrons in a bonding orbital.

Bond order

If then the molecule is said be stable. However, if than the molecule is considered to be unstable.

Bond order of can calculated from its electronic configuration as:

Number of bonding electron,

Number of anti-bonding electrons,

Bond order of nitrogen molecule

There are 16 electrons in a Dioxygen molecule, 8 from each oxygen atom. The electronic configuration of oxygen molecule can be written as:

Since the 1s orbital of each oxygen atom is not involved in bonding, the number of bonding electrons and the number of anti-bonding electrons

Bond order

Hence, the bond order of oxygen molecule is 2.

Similarly, the electronic configuration of can be written as:

Bond order of

= 2.5

Thus, the bond order of is .

The electronic configuration of ion will be:

Bond order of

Thus, the bond order of