Question

According to VSEPR model, what makes the shapes of ${CH}_4,{NH}_3$ and $H_{2}O$ different?

• A. The presence of different number of $H-$atoms in the central atom
• B. Different central atoms
• C. Different of lone pairs of electrons on the central atoms which apply different total repulsion
• D. All of the above

Answer 1

The correct option is C Different of lone pairs of electrons on the central atoms which apply different total repulsion

The main postulates of the VSEPR theory are as follows:

• The shape of a molecule depends upon the number of valence shell electron pairs (bonded or nonbonded) around the central atom.

• Pairs of electrons in the valence shell repel one another since their electron clouds are negatively charged.

• These pairs of electrons tend to occupy such positions in space that minimise repulsion and thus maximise the distance between them.

• The valence shell is taken as a sphere with the electron pairs localising on the spherical surface at a maximum distance from one another.

• Multiple bonds is treated as if it is a single electron pair and the two or three electron pairs of a multiple bond are treated as a single super pair.

• Where two or more resonance structures can represent a molecule, the VSEPR model is applicable to any such structure.

Hence, VSEPR theory gives the shape of the molecule considering lone pairs on the central atom which results in repulsion and thus gets a particular shape.

Hence, option $C$ is the correct answer.