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Question #44250

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The Question

Consider the heteronuclear diatomic molecule \ce{CO} at 298 K. It exhibits an anomalously small dipole moment ( $\approx 0.112$ D) with the negative end residing on the less electronegative Carbon atom. Furthermore, its bond length ( $1.128$ \AA) deviates from predictions based on the simple summation of isolated atomic covalent radii. Based on Molecular Orbital (MO) theory and the concept of Radial Probability Distribution (RPD), which of the following statements correctly identifies the underlying quantum mechanical cause of these anomalies?

Options

A.
Strong 2s-2p mixing on Carbon shifts the RPD maximum of the $5\sigma$ (HOMO) orbital outward, away from the internuclear axis, creating a directional lone pair that reverses the expected dipole moment and invalidates simple atomic radii summations.
B.
2s-2p mixing decreases the effective nuclear charge ( $Z_{eff}$ ) on Oxygen, causing its 2p RPD to expand, which shifts the center of negative charge to Carbon and increases the bond length beyond standard covalent radii.
C.
The large energy gap between C(2s) and O(2p) prevents MO mixing, maintaining a spherically symmetric RPD for the Carbon 2s electrons. The dipole moment is reversed solely due to $\pi$ -backbonding from Oxygen to Carbon.
D.
2s-2p mixing introduces an additional radial node in the $5\sigma$ orbital, contracting the electron density towards the internuclear axis, which explains the unusually short \ce{C-O} bond length but fails to explain the dipole direction.

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Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

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Concepts Behind This Question

Radial Probability Distribution|Molecular Orbital Mixing

Why This Question Is Tricky

Common Mistakes

The question tests the 'Chemical Exception' of heteronuclear diatomic polarity and the breakdown of isolated-atom models.

Students often assume the Radial Distribution Function (RDF) of a 2s orbital remains constant and spherically symmetric regardless of bonding, leading them to predict bond lengths via simple atomic radii summation and dipole moments via pure electronegativity differences.

The hidden variable is 2s-2p MO mixing, which asymmetrically distorts the RPD of the HOMO ( $5\sigma$ ), creating a directional lone pair on Carbon that reverses the dipole moment and alters the effective covalent radius.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Structure of Atom - Class 11 Part 1
Concept	Radial Probability Distribution
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free