Question

Which of the following is a polar molecule ?

• A. $XeF_4$
• B. $BF_3$
• C. $SF_4$
• D. $SiF_4$

Answer 1

The Correct Option is C

To identify which molecule among $XeF_4$, $BF_3$, $SF_4$, and $SiF_4$ is polar, we need to examine their molecular geometry and the distribution of electron density (i.e., whether the molecular shape causes an unequal distribution of charge).

1. Polarity in molecules is mainly due to the difference in electronegativity between the central atom and the atoms surrounding it. However, the symmetry of the molecule can cancel out individual bond polarities, resulting in a non-polar molecule.
2. Analyzing each molecule:
   1. $XeF_4$: Xenon tetrafluoride has a square planar geometry, which is symmetrical. The dipoles from the Xe-F bonds cancel out because they are evenly distributed in opposite directions. Hence, $XeF_4$ is non-polar.
   2. $BF_3$: Boron trifluoride has a trigonal planar shape. Due to its symmetry, the dipole moments from the B-F bonds cancel each other out, making $BF_3$ non-polar.
   3. $SF_4$: Sulfur tetrafluoride has a seesaw shape due to the presence of a lone pair on sulfur. This asymmetry results in a net dipole moment, making $SF_4$ a polar molecule.
   4. $SiF_4$: Silicon tetrafluoride has a tetrahedral shape. The symmetry of the molecule means that the dipole moments from the Si-F bonds cancel, rendering $SiF_4$ non-polar.
3. From the analysis above, $SF_4$ is the only molecule that is polar due to its asymmetric tetrahedral (seesaw) geometry, leading to unequal distribution of charge.
4. Thus, the correct answer is $SF_4$.