1) how many valence electrons are in a structure with the formula C3H3NOS? 

I calculated 52 total electrons less the 28 used by first, second, and third shells equals 24 valence electrons, which was incorrect.

2) predict the relative lengths of the carbon-halogen bonds in CH3F, CH3Cl, and CH3Br. Order longest to shortest.

I determined CH3Cl > CH3Br > CH3F, which was incorrect.

3) predict the relative strengths of the carbon-halogen bonds in CH3F, CH3Cl, and CH3Br. Order strongest to weakest.

I know there is an inverse relationship between bond length and strength, but since my answer to 2) above was incorrect, my answer for 3) was also incorrect.

4) predict the approximate bond angle for C-N-C bond angle in (CH3)2NH. Choices are 120.0, 109.5, 107.3 (my answer) and 104.5. I did not submit this one yet.

5) predict the approximate bond angle for C-N-C bond angle in (CH3)2+NH2. Same choices as in 4) above. My answer is 109.5. I did not submit this one yet.


Additional Requirements 

Other Requirements: Please include supporting calculations and/or explanations. More important that I understand and know how to approach these types of problems on a test. I thought that my initial answers were correct.