Effect Of Lone Pairs On The Shape Of Molecules

Question 1

How do we deal with lone pairs? (Key facts.)

Answer 1

Lone pairs repel more strongly than bonding pairs.
This extra repulsion decreases other bond angles by 2.5 degrees.

Question 2

Normally the tetrahedral bond angle is 109.5 degrees. What would the bond angle be with a lone pair?

Answer 2

Lone b pair repelled more strongly than a bonding pair.

This extra repulsion reduces the bonding angle by 2.5 degrees.

So it would be “107 degrees”.

So it is Called “pyramidal” because it looks like a pyramid.

Question 3

When a central atom has bond pairs and two sets of lone pairs, what shape is it based on?

Answer 3

The regular “tetrahedron” which has a bond angle of 109.5 degrees.

Because there at two lone pairs the bond angle will be decreased by (2.5+2.5) 5 degrees which will reduce it to 104.5 degrees.

This molecule is called a “ non-linear” or a “ V-shaped” molecule.