Question

Why are the bond angles in methane, chloromethane, ammonia and water not the same?

Why are the bond angles in methane, chloromethane, ammonia and water not the same?

Answer

Several reasons:

(1) The number of bonds in each determines the angle of the bonds, this is because bonded pairs of electrons repel apart from one another as far as possible.

(2) Lone pairs have their own repulsion and repel other bonded pairs of electrons and reduce all other bond angles by 2.5 degrees.

These are the two main contributing factors.

Example of lone pairs affecting bond angles:

-H2O is non-linear only due to its two lone pairs, if they were not present then water would be linear (flat, straight) however instead they make a V shape.

Jan 7 at 18:26

All are derived from a tetrahedral carrangement which should produce bond angles of 109.5 degrees.

However, lone npairs (ammonia, water) take up more space and tend to "squeeze" the bonds a bit. Same for Cl which is a rather large atom.

I would arrange them from highest (109.5) to lowest as follows:

CH4; CH3Cl (because of the big Cl); NH3 (because of one lone pair on the nitrogen) and lastly H2O (because of two lone pairs on the oxygen)

Jan 7 at 22:12