VSEPR Shapes of Molecules

We know that VSPER theory minimizes the force between the bond pair and lone pair electrons of atoms and the structure so formed also follows this rule. So using this theory we can easily predict the shape of the molecule if all the bond pairs and the lone pairs of the molecule are known to us.

The force of repulsion between Lone Pair- Lone Pair, Lone Pair- Bond Pair, Bond Pair- Bond Pair (BP – BP) is in the order mentioned below:

Lone Pair- Lone Pair (LP – LP) > Lone Pair- Bond Pair (LP – BP) > Bond Pair- Bond Pair (BP – BP)

Now we can predict the shape of the molecule by first finding the total electron pairs around the central atom using the formula,

Total Electron Pairs =  ½ (Number of Valence Electrons of Central Atom + Number of atoms attached to Central Atom by single bonds)

For Negative and Positive ions electron pairs are calculated as,

Negative Ions: In negative ions, we add the number of electrons equal to the units of negative charge on the ion to the valance electrons of the central atom.

Positive Ions: In positive ions, we subtract the number of electrons equal to the units of positive charge on the ion from the valance electrons of the central atom.

• If we have only two atoms then the shape of the molecule so formed is linear.
• If the central atom is only surrounded by the bond pair of similar atom then the structure of the atom is symmetrical and have regular geometry.
• If the central atom is only surrounded by the bond pairs and lone pair of electrons then the structure of the atom is unsymmetrical because of the lone pair-lone pair and bond pair-lone pair repulsions, and thus the structure so formed have a distorted geometry.

VSEPR Theory tells us about the basic structure of the molecules based on the force of repulsion between lone pair and bond pair of electrons. It states that any molecule arranged in such a structure minimizes the repulsion between the lone pair and bond pair of the molecule.

Let’s learn more about VSEPR theory in detail, including its postulates, limitations, and examples.