Question 14 Marks
The molecular orbital theory is based on the principle of a linear combination of atomic orbitals. According to this approach when atomic orbitals of the atoms come closer, they undergo constructive interference as well as destructive interference giving molecular orbitals, i.e., two atomic orbitals overlap to form two molecular orbitals, one of which lies at a lower energy level (bonding molecular orbital). Each molecular orbital can hold one or two electrons in accordance with Pauli's exclusion principle and Hund's rule of maximum multiplicity.
For molecules up to $N _2$, the order of filling of orbitals is:
Bond order $=\frac{1}{2}$ [bonding electrons - antibonding electrons]
Bond order gives the following information:
I. If bond order is greater than zero, the molecule/ion exists otherwise not.
II. Higher the bond order, higher is the bond dissociation energy.
III. Higher the bond order, greater is the bond stability.
IV. Higher the bond order, shorter is the bond length.
1. Arrange the following negative stabilities of $CN , CN ^{+}$and $CN ^{-}$in increasing order of bond. (1)
2. The molecular orbital theory is preferred over valence bond theory. Why? (1)
3. Ethyne is acidic in nature in comparison to ethene and ethane. Why is it so? (2)
OR
Bonding molecular orbital is lowered by a greater amount of energy than the amount by which antibonding molecular orbital is raised. Is this statement correct? (2)
For molecules up to $N _2$, the order of filling of orbitals is:
Bond order $=\frac{1}{2}$ [bonding electrons - antibonding electrons]
Bond order gives the following information:
I. If bond order is greater than zero, the molecule/ion exists otherwise not.
II. Higher the bond order, higher is the bond dissociation energy.
III. Higher the bond order, greater is the bond stability.
IV. Higher the bond order, shorter is the bond length.
1. Arrange the following negative stabilities of $CN , CN ^{+}$and $CN ^{-}$in increasing order of bond. (1)
2. The molecular orbital theory is preferred over valence bond theory. Why? (1)
3. Ethyne is acidic in nature in comparison to ethene and ethane. Why is it so? (2)
OR
Bonding molecular orbital is lowered by a greater amount of energy than the amount by which antibonding molecular orbital is raised. Is this statement correct? (2)
Answer
View full question & answer→1. The increasing order of negative stabilities of $CN , CN ^{+}$and $CN ^{-}$is $CN ^{+}> CN > CN ^{-}$.
2. The molecular orbital theory is preferred over valence bond theory because molecular orbital theory explains the magnetic nature of the molecule.
3. In ethyne, hydrogen atoms are connected to $s p$ hybridized carbon atoms, but in ethene, they are attached to $sp ^2$ hybridized carbon atoms and in ethane, they are attached to $sp ^3$ hybridized carbons.
OR
The given statement is not correct because the bonding molecular orbital is lowered by a lesser amount of energy than the amount by which antibonding molecular orbital is raised.
2. The molecular orbital theory is preferred over valence bond theory because molecular orbital theory explains the magnetic nature of the molecule.
3. In ethyne, hydrogen atoms are connected to $s p$ hybridized carbon atoms, but in ethene, they are attached to $sp ^2$ hybridized carbon atoms and in ethane, they are attached to $sp ^3$ hybridized carbons.
OR
The given statement is not correct because the bonding molecular orbital is lowered by a lesser amount of energy than the amount by which antibonding molecular orbital is raised.