Chemistry Class 11 NCERT Solutions: Chapter 4 Chemical Bonding and Molecular Structure Part 9
Q: 39. Define hydrogen bond. Is it weaker or stronger than the van der Waals forces?
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.
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
Hence, the bond order of oxygen molecule is 2.
Similarly, the electronic configuration of can be written as:
Bond order of
Thus, the bond order of is .
The electronic configuration of ion will be:
Bond order of
Thus, the bond order of