The total number of molecules with zero dipole moment among $\ce{CH4}$, $\ce{BF3}$, $\ce{H2O}$, $\ce{HF}$, $\ce{NH3}$, $\ce{CO2}$ and $\ce{SO2}$ is _____.

JEE Main · 2024 · 29 Jan 2024 · Shift 2 · Chemical Bonding and Molecular Structure

The total number of molecules with zero dipole moment among

CH X_{4}

BF X_{3}

H X_{2} O

HF

NH X_{3}

CO X_{2}

and

SO X_{2}

is _____.

Answer: 3

A molecule has zero net dipole moment when its geometry is symmetric enough that the individual bond dipoles cancel.

C H_{4}

is tetrahedral with four identical C–H bonds arranged symmetrically — the dipoles cancel.

B F_{3}

is trigonal planar with three identical B–F bonds at

12 0^{\circ}

— the dipoles cancel.

C O_{2}

is linear with two identical, oppositely directed C=O dipoles that cancel exactly.

H_{2} O

(bent),

N H_{3}

(pyramidal) and

S O_{2}

(bent) are all asymmetric, with a lone pair distorting the geometry so their bond dipoles do not cancel;

HF

, a heteronuclear diatomic, is polar by definition.

Three molecules —

C H_{4}

B F_{3}

and

C O_{2}

— have zero dipole moment.

JEE Main · 2024 · 29 Jan 2024 · Shift 2 · Integer answer