JEE Advanced 2022 · Paper 1 · Chemistry Q9

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ChemistryMultiple correct+4 / -2Question 45 of 54

For diatomic molecules, the correct statement(s) about the molecular orbitals formed by the overlap of two $2p_z$ orbitals is(are)

\sigma

orbital has a total of two nodal planes.

\sigma^*

orbital has one node in the

xz

-plane containing the molecular axis.

\pi

orbital has one node in the plane which is perpendicular to the molecular axis and goes through the center of the molecule.

\pi^*

orbital has one node in the

xy

-plane containing the molecular axis.

Answer and worked solution

Official answer: A, D

Take the $\sigma$ orbitals from head-on overlap of $2p_z$ along the molecular axis, and the $\pi$ orbitals from side-on overlap with the axis in the $xy$ -plane.

(A) The bonding $\sigma(2p_z)$ orbital has two nodal surfaces perpendicular to the axis, behind each nucleus. Counting these as nodal planes makes (A) true. The official key accepts A, D or D alone because of this ambiguity.

(B) False. $\sigma^*$ has its node in the plane perpendicular to the axis, midway between the nuclei. It has no node in a plane containing the axis.

(C) False. A node perpendicular to the axis through the centre belongs to $\pi^*$ , not $\pi$ .

(D) True. $\pi^*$ has a nodal plane containing the axis (the $xy$ -plane) as well as the perpendicular one.

Topics:Molecular orbital theory Orbitals and their shapes

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JEE Advanced 2022 · Paper 1, Chemistry question 9