Question

Which of the molecules below will be polar?

CS2, BF3, SO2, CH3Br

	CH3Br only
	CS2 only
	Both BF3 and CH3Br
	Both SO2 and CH3Br

Answer 1

Concepts and reason

For the given molecules, draw the structures based on the VSEPR. Identify the polar bonds in the molecules. Also check for the lone pair present in the molecule. Presence of polar bonds and lone pair indicate that polarity is present in the molecule. Unsymmetrical molecules also have polarity.

Fundamentals

Valence Shell Electron Pair Repulsion Theory(VSEPR) is used to predict the geometry of a molecule. This theory is based on the electrostatic repulsion. The lone pairs and bond pairs present in the molecule arrange themselves in a way that they experience minimum repulsion.

The sequence followed to determine the repulsive order is as follows:

Lone pair $-$ lone pair $>$ Lone pair $-$ bond pair $>$ Bond pair $-$ bond pair

The lone pairs and bond pairs present in the molecule arrange themselves in a way that they experience minimum repulsion.

Polar nature arises in a molecule due to the difference in the electronegativity of the bonded elements. The electronegative element pulls the electron cloud of the bonded electrons towards itself. This behaviour develops a small negative charge on the more electronegative element.

The bond formed by the elements having difference in electronegativity give rise to a polar molecule. When the molecule is unsymmetrical, the structure of the molecule gives rise to the polarity of the molecule.

The structure of the given molecules is drawn as follows:

The molecules with the polarity are shown as follows:

Ans:

Among the given molecules, the polar molecules are as follows: