Rationalization of bond angle/ bond pair repulsions.

[admXXII]

Homework Statement

I need help rationalizing the following:
a) Bond angle for H₂S is only 92^o whereas bond angle for H₂O is 104.5^o.

b) If bond-pair<-> bond-pair repulsion is maximum for the C-H bonds in CH₃X, ∑ all bond angles is 450^o for CH₃X

c) For CH₂Br₂, the H-C-Br will be the smallest bond angle observed.

Homework Equations

main considerations:
a) magnitude of central atom non-bonding pairs<->single bonding pairs repulsion w/ bonding-pair <-> bonding pair.

b) I got nothing

c) Br- Br repulsion? Magnitude of Br

The Attempt at a Solution

see main considerations

I realize this is a lot. I appreciate any help/ guidance from someone with a firm grasp on this stuff.
Thanks in advance.

 

[nate808]

a) The difference in bond angles between H2S and H2O can be explained by the difference in electronegativity between sulfur and oxygen. Oxygen is more electronegative than sulfur, meaning it has a stronger pull on electrons. This results in a greater bond-pair<->bond-pair repulsion in H2O, causing the bond angle to be larger compared to H2S. Additionally, H2O has two lone pairs of electrons on the central oxygen atom, which also contribute to the smaller bond angle by pushing the bonding pairs closer together.

b) The total sum of bond angles in CH3X is 360 degrees. However, the bond angles are not all equal due to the different electronegativities of the atoms involved. The C-H bonds will have the smallest bond angles due to the difference in electronegativity between carbon and hydrogen. The bond-pair<->bond-pair repulsion between these bonds will be maximum, hence the smaller bond angles. The total sum of bond angles being greater than 360 degrees can be explained by the presence of lone pairs on the central carbon atom, which also contribute to the bond angle.

c) In CH2Br2, the H-C-Br bond angle will be the smallest observed due to the presence of two larger bromine atoms on either side of the central carbon atom. This results in a greater magnitude of Br-Br repulsion, pushing the H-C-Br bond angle closer together. Additionally, the lone pairs on the central carbon atom also contribute to the smaller bond angle by pushing the bonding pairs closer together.