Question

Is the molecule ${\mathrm{SF}}_4$ polar or non-polar?

Answer 1

VSEPR Theory postulates:

• The shape of the molecule is determined by the total number of electron pairs(bonding and nonbonding) around the central atom and the orientation of these electron pairs in the space around the central atom.
• In order to minimize the repulsive forces between them, electron pairs around the central atom, tend to stay as far away from each other as possible.
• Electron pairs around the molecule's central atom can be shared or can be lone pairs. The 'shared pairs' of electrons are also called bond pairs of electrons. The presence of lone pair of electrons on the central atom causes some distortions in the expected regular shape of the molecules.
• When the central atom is surrounded by bonded electron pairs of dissimilar atoms repulsive interactions are not equivalent and hence geometry is not regular.
• When the central atom is surrounded by bonded electron pairs and lone pairs not involved in bonding, repulsive interactions are not equivalent, and hence molecular geometry will be irregular.
• The strength of repulsions between different electron pairs follows the order, lone pair-lone pair > lone pair-bond pair > bond pair-bond pair.

${\mathrm{SF}}_4$ molecule:

• To determine if a molecule is polar or nonpolar, draw its Lewis Structure and check its molecular geometry.
• If there is an odd number of lone pairs of electrons around the central atom, then the molecule is polar.
• If there is an even number of lone pairs, check the VSEPR structure to decide.
• The lewis structure of ${\mathrm{SF}}_4$ molecules is,
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• Here, only one lone electron pair is present around the sulfur atom; thus molecule is polar.
• According to VSEPR theory, the molecular geometry of ${\mathrm{SF}}_4$ is a see-saw shape.
• Two of the $\mathrm{S}-\mathrm{F}$ bonds are pointing away from each other, so their bond dipoles get canceled.
• The other two $\mathrm{S}-\mathrm{F}$ dipoles are pointing down, their bond dipoles do not cancel, so the molecule is polar.

Therefore, the ${\mathrm{SF}}_4$ molecule is polar.