Question

1. Draw the possible resonance structures for [S2CN(CH3)2]- and assign formal charges. Indicate which resonance structure provides the best description for the ion and why?

2. Predict and draw the Lewis dot structures for the following compounds. Include a description of distortion from ideal geometry and why.

a) [IF3]2-

b) XeO2F2

3. Predict the order of solubility in water for the following series, and explain the factors involved.

PbCl2 PbBr2 PbBI2 PbS

4. Draw all isomers for the compound [Cr(H2O)3Br(Cl)(I)] . Indicate any enantiomer pairs.

Answer 1

1.

The possible resonance structures for are shown below.

The ion is named dimethyldithiocarbamate.

The resonance structures I and III provides the best description for the ion as they have least charges.
Resonance forms become less significant as the number of charges are increased.

2.

a)

The Lewis dot structure is shown below.

There are three bond pairs and 3 lone pairs of electrons on central I atom. The electron pair geometry is octahedral and molecular geometry is T-shaped. The F-I-F bond angle is less than 90 degree (octahedral bond angle) due to lone pair - bond pair repulsion.

b)

The Lewis dot structure is shown below.

The central Xe atom has 4 bonding domains and one lone pair of electrons. The electron pair geometry is trigonal bipyramidal and molecular geometry is sea saw shaped. The O=Xe=O and F-Xe-F bond angles are slightly lower than that expected on the basis of trigonal bipyramidal geometry due to lone pair - bond pair repulsion.