Q.25 The molecule(s) with non–zero dipole moment is/are
(A) N2
(B) CO2
(C) NO
(D) SO2

NO and SO2 have non-zero dipole moments, while N2 and CO2 have zero dipole moments.

Option Analysis

(A) N2

Nitrogen molecule (N2) consists of two identical nitrogen atoms with a triple bond. Both atoms have the same electronegativity (3.0), resulting in no charge separation and zero dipole moment.

(B) CO2

Carbon dioxide (CO2) has a linear structure (O=C=O) with two polar C=O bonds. The dipole moments are equal in magnitude but opposite in direction, canceling each other out for a net zero dipole moment.

(C) NO

Nitric oxide (NO) features a polar N=O bond due to electronegativity difference (N: 3.0, O: 3.5). The diatomic structure yields a net dipole moment of approximately 0.15-0.16 D.

(D) SO2

Sulfur dioxide (SO2) adopts a bent V-shaped geometry with O-S-O bond angle ~119°. The two polar S=O bonds produce dipole moments that do not cancel, resulting in a net dipole moment of ~1.6 D.

Correct answer: (C) and (D).

Molecules with non-zero dipole moment play a key role in understanding molecular polarity, crucial for CSIR NET chemistry and life sciences exams. This article breaks down N2, CO2, NO, and SO2 based on structure, electronegativity, and symmetry.

Dipole Moment Basics

Dipole moment measures charge separation in a molecule, calculated as charge times distance (in Debye units). Polar bonds arise from electronegativity differences, but net dipole depends on vector sum. Symmetry often cancels individual dipoles in non-polar molecules.

Why N2 Has Zero Dipole Moment

N2 is non-polar with identical N atoms sharing electrons equally in a triple bond. Linear diatomic shape ensures no net polarity.

CO2: Linear Cancellation

CO2’s linear O=C=O geometry features two C=O dipoles pointing oppositely. Despite polar bonds, perfect symmetry yields zero net dipole moment.

NO: Weakly Polar Diatomic

NO exhibits a small dipole moment (~0.15 D) from N-O electronegativity difference in its diatomic structure. No cancellation occurs.

SO2: Bent and Polar

SO2’s bent shape (lone pair on S) prevents S=O dipole cancellation, producing ~1.6 D net moment. This contrasts with linear CO2.