Dot and Cross Diagrams.. How do i do these!?

Question

Many thanks for any help you can give me, this question is numbing my brain! lol

1. (a) (i) Draw a dot & cross diagram to show the bonding in hydrogen sulphide, H2S. State and explain the shape of H2S using the 'electron pair repulsion theory', estimating the bond angle.

(ii) Hydrogen sulphide (H2S) is a gas at room temperature whereas water (H2O) is a liquid boiling at 100oC. Suggest an explanation for this.

(b) (i) Draw a dot & cross diagram to show the bonding in methanal, HCHO. State and explain the shape of HCHO using the 'electron pair repulsion theory', estimating the (H-C-H) bond angle.

(ii) Methanal (HCHO) is a gas at room temperature whereas methanol (CH3OH) is a liquid. Suggest an explanation for this.

Answer 1

Dot and cross diagrams are used to show the electronic positioning in bonding with two different atoms. So for example, for the first question, you would draw a circle to indicate the nucleus of each of the atoms H and S, and either use dots to indicate the H electrons & crosses to indicate the S electrons, or vice versa. It's basically to make clear that covalent bonds such as those found in H2S involve an electron from each of the atoms involved.

Answer 2

This sounds tricky!
I am not sure and don't want to tell you the wrong thing.
Try www.askjeeves.com