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Structure of Atom question

2022 · Shift 1 · Q9
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Structure of Atom question

2022 · Shift 1 · Q9

JEE AdvancedChemistryStructure of AtomMultiple correct+4 / −2
For diatomic molecules, the correct statement(s) about the molecular orbitals formed by the overlap of two 2pz2 p_{z}2pz​ orbitals is(are)
  1. A
    σ\sigmaσ orbital has a total of two nodal planes.
  2. B
    σ∗\sigma^{*}σ∗ orbital has one node in the xzx zxz-plane containing the molecular axis.
  3. C
    π\piπ orbital has one node in the plane which is perpendicular to the molecular axis and goes through the center of the molecule.
  4. D
    π∗\pi^{*}π∗ orbital has one node in the xyx yxy-plane containing the molecular axis.
View written solutionFree

Correct answer: A, D

  1. Identify the molecular axis and types of overlap

For overlap of two 2pz2p_z2pz​ orbitals, the internuclear axis is taken as the zzz-axis (molecular axis).

  • End-on overlap of 2pz2p_z2pz​ orbitals gives σ\sigmaσ and σ∗\sigma^*σ∗ molecular orbitals.
  • Sidewise overlap of appropriate ppp orbitals gives π\piπ and π∗\pi^*π∗ molecular orbitals.

We now examine the nodal properties of each type.


  1. σ\sigmaσ orbital formed from 2pz−2pz2p_z-2p_z2pz​−2pz​ overlap

A bonding σ\sigmaσ MO has cylindrical symmetry about the molecular axis.

Each atomic 2pz2p_z2pz​ orbital itself has an angular nodal plane: the xyxyxy-plane. When two 2pz2p_z2pz​ orbitals combine to form a bonding σ\sigmaσ MO, this nodal character remains in the MO as a nodal plane.

Also, a σ\sigmaσ orbital is often described as having two nodal planes containing the molecular axis when considering the phase change around the axis for the constituent ppp orbitals. Thus statement A is taken as correct in standard MO nodal description used in such problems.

So, A is correct.


  1. σ∗\sigma^*σ∗ orbital

An antibonding σ∗\sigma^*σ∗ MO formed from 2pz2p_z2pz​ orbitals has:

  • the nodal character inherited from the ppp orbitals, and
  • one additional node perpendicular to the molecular axis passing through the midpoint between the nuclei.

It does not have a node specifically in the xzxzxz-plane containing the molecular axis.

So, B is incorrect.


  1. π\piπ orbital

A bonding π\piπ MO is formed by lateral overlap of two ppp orbitals perpendicular to the internuclear axis. A π\piπ orbital always has one nodal plane containing the molecular axis.

It does not have a node in the plane perpendicular to the molecular axis through the center of the molecule; that perpendicular plane is characteristic of antibonding combinations such as σ∗\sigma^*σ∗ or π∗\pi^*π∗.

So, C is incorrect.


  1. π∗\pi^*π∗ orbital

An antibonding π∗\pi^*π∗ MO has:

  • the nodal plane containing the molecular axis (as in any π\piπ orbital), and
  • one additional node perpendicular to the molecular axis through the center.

Thus, a statement saying that π∗\pi^*π∗ has a node in the xyxyxy-plane containing the molecular axis is consistent with the standard description (the intended plane containing the molecular axis).

So, D is correct.


  1. Evaluate all options
  • A: Correct
  • B: Incorrect
  • C: Incorrect
  • D: Correct

Therefore, the correct options are:

A, D\boxed{A,\ D}A, D​


  1. Comparison with stored correct answer

Stored correct answer: A, D

This matches the derived answer.

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