Question

Which of the following has zero dipole moment?

• A. $\mathrm{ClF}$
• B. ${\mathrm{PCl}}_3$
• C. ${\mathrm{SiF}}_4$
• D. ${\mathrm{CFCl}}_3$

Answer 1

The correct option is C

${\mathrm{SiF}}_4$

Explanation for correct option

(C) ${\mathbf{SiF}}_{\mathbf{4}}$

Dipole moment

• A dipole moment is a measure of the distance between two opposing electrical charges.
• Dipole moments are measured as vector quantities.

${\mathbf{SiF}}_{\mathbf{4}}$

• ${\mathrm{SiF}}_4$ has regular tetrahedral geometry and symmetric molecule.
• Hence, its dipole moments get cancelled due to different electronegativities of silicon $\left(\mathrm{Si}\right)$ and fluorine $\left(\mathrm{F}\right)$.
• Structure is as follows:

Explanation for incorrect options

(A) $\mathbf{ClF}$

• $\mathrm{ClF}$ has a linear shape.
• Chlorine $\left(\mathrm{Cl}\right)$ and Fluorine $\left(\mathrm{F}\right)$ have different electronegativities.
• Hence, the $\mathrm{Cl}-\mathrm{F}$ bond is polar, and has a dipole moment.

(B) ${\mathbf{PCl}}_{\mathbf{3}}$

• The existence of a lone pair of electrons at the top of the molecule, which causes electron-electron repulsion in ${\mathrm{PCl}}_3$.
• The ${\mathrm{PCl}}_3$ is a polar molecule.
• This produces a bent structure, which unequally distributes charge across the molecule, resulting in a permanent dipole.

(D) ${\mathbf{CFCl}}_{\mathbf{3}}$

• Since chlorine is more electronegative than carbon in the ${\mathrm{CFCl}}_3$, it attracts electrons in the $\mathrm{C}—\mathrm{Cl}$ bond.
• Hence, it has a net dipole moment.

Therefore, the correct option is (C) ${\mathbf{SiF}}_{\mathbf{4}}$.