Question

9.1 Explain the concepts of the VSEPR model.

1. Explain why molecules take the shapes they have

2. Define an electron domain

3. Draw dot diagrams and determine appropriate domain geometry based on the diagram

4. From the dot diagram and the domain geometry, determine approximate bond angles is

   a substance.

9.2 Determine the molecular geometries of molecules.

1. Draw a dot diagram or when given a dot diagram determine the appropriate molecular geometry

2. Explain why non-bonding pairs and double and triple bonds cause the other bond angles to be slightly less than ideal

Answer 1

9.1) VSEPR is The Valence Shell Electron Pair Repulsion model determines the bonding and the geometry of molecules by the number of lone pair and bond pair of electrons in the valence shell of the central atom.

If the central atom is surrounded by the only bond pair of electron then the molecule will have regular geometry whereas if the central atom is surrounded by both lone pair and bond pair of electrons then the molecule will have irregular geometry.

Bond angles involving multiple bonds are larger than those involving single bonds.

Repulsion between shell having filled with electrons is larger than those shells having incompletely filled with electrons

In AB molecule, B-A-B bond angle decreases with an increase in electronegativity of atom B

Repulsion between lone pair and lone pair is greater than the lone pair and bond pair, bond pair and bond pair of electrons

a) Molecules take the shape they have because each atom in a molecule will achieve the geometry that minimizes the repulsion between electrons in the valence shell of that atom.

b) Electron domain: Number of lone pairs around the particular atom is known as the electron domain. It is also known as electron groups.

Dot diagram of SO2 is attached below in 9.2

Its domain geometry is trigonal planar because sulfur has 3 electron domains that mean it has 6 valence electrons from which it forms 2 single bonds with 2 oxygen atoms and it contains one non-bonding lone pair.

As the sulfur atom is bonded to two oxygen atom it causes repulsion to form 120 degree bond angle.

9.2) Dot diagram and molecular geometry of SO2

Molecular geometry of SO2 is bent because of the difference between the electronegativity of sulfur and oxygen atom. As the difference between the polarity of both atoms is greater than zero which influences bond angle to be bent geometry.

If there is no lone pair on central atom then molecular geometry and electron domain geometry is the same for example CCl4 has a tetrahedral shape.

Due to the electrostatic repulsion between the electrons of a double bond, triple bond and non-bonding make the most stable arrangement of groups that minimizes the repulsion and attain lowest energy molecular structure.