How can the VSEPR Theory be used to Predict the Shapes of Molecules? An artical by The othentic One

 

How can the VSEPR Theory be used to Predict the Shapes of Molecules?

 

The strength of the repulsion between a lone pair and a bond pair of electrons lies in between the repulsion between two lone pairs and between two bond pairs. The order of repulsion between electron pairs is as follows:
 

Lone Pair- lone pair > Lone Pair- bond- pair > Bond Pair- bond pair.

 

1. Total number of electron pairs around the central atom = ½ (number of valence electrons of central atom + number of atoms linked to central atom by single bonds)

 

For negative ions, add the number of electrons equal to the units of negative charge on the ions to the valence electrons of the central atom.

For positive ions, subtract the number of electrons equal to the units of positive charge on the ion from the valence electrons of the central atom.

2. The number of Bond pair = Total number of atoms linked to central atom by single bonds.

 

3. Number of lone pairs = Total number of electron – No of shared pair

 

• The electron pairs around the central atom repel each another and move so far apart from each another that there are no greater repulsions between them. This results in the molecule having minimum energy and maximum stability.
• The shape of a molecule with only two atoms is always linear.
• For molecules with three or more atoms, one of the atoms is called the central atom and other atoms are attached to the central atom.
• If the central atom is linked to similar atoms and is surrounded by bond pairs of electrons only, the repulsions between them are similar as a result the shape of the molecule is symmetrical and the molecule is said to have regular geometry.
• If the central atom is linked to different atoms or is surrounded by bond pair as well as a lone pair of electrons, the repulsion between them is similar. As a result, the shape of the molecule has an irregular or distorted geometry.
• The exact shape of the molecule depends upon the total number of electron pairs present around the central atom.

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