JEE Advanced 2022 Paper 1 · Q09 · Molecular Orbital Theory

Question

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

SolveKar AI · Accepted Answer

Take the molecular (internuclear) axis as the z-axis. Head-on overlap of two 2p$_z$ orbitals forms $\sigma_{2p_z}$ and $\sigma^*_{2p_z}$; sideways overlap (of 2p$_x$ or 2p$_y$) would form $\pi$ orbitals, but the question is specifically about overlap of two 2p$_z$ orbitals, which only produces $\sigma$ and $\sigma^*$.

(A) The $\sigma_{2p_z}$ orbital is formed from two 2p$_z$ atomic orbitals, each of which has its own nodal plane perpendicular to the axis (the xy-plane through each nucleus). These two nodal planes are preserved in the bonding combination — so $\sigma$ has two nodal planes (one at each nucleus, perpendicular to the molecular axis). TRUE.

(B) The $\sigma^*_{2p_z}$ antibonding orbital has a nodal plane in the middle of the molecule perpendicular to the molecular axis (the xy-plane), not in the xz-plane. FALSE.

(C) For a $\pi$ orbital (formed from 2p$_x$ or 2p$_y$), the node is the plane containing the molecular axis (e.g., the yz- or xz-plane for $\pi_x$ or $\pi_y$), not a plane perpendicular to the molecular axis. Moreover, this overlap is not between two 2p$_z$ orbitals. FALSE.

(D) A $\pi^*_{2p_x}$ orbital (antibonding) has its node in the xy- … [truncated]

JEE Advanced 2022 Paper 1 · Q09 · Molecular Orbital Theory

Solution