NAME:_____________________________ CHEM 1311, Section B Second Exam 18th February WRITE YOUR NAME IN BLOCK CAPITALS ON THE TOP OF EACH SHEET

NO CALCULATOR IS ALLOWED FOR THIS TEST In taking this examination your are expected to adhere to the GT academic honor code. At a minimum this requires that you utilize only the materials supplied to you, and that you do not give help to, or accept help from, others. 1) For each of the molecules in the following list you should use VSEPR to predict

the shape of the molecule. As part of each answer you should indicate how many pairs of electrons are involved in bonding to the central atom, you should draw the structure of the molecule and indicate on the structural drawing the location of any lone pairs that may be present on the central atom, and you should state what the shape of the molecule is.

a) PH3

4 pairs of electrons, pyramidal

PH

HH

b) IF5 6 pairs of electrons, square pyramidal

F F

FFI

F

c) PCl5

5 pairs of electrons, trigonal bipyramidal

ClPClCl

ClCl

NAME:_____________________________

d) BrF3

5 pairs of electrons, T-shaped

FBrFF

e) SF4

5 pairs of electrons, saw-horse

SF

F

FF

2) For each of the following molecules state the hybridization state (spn or spndx) of

the valence orbitals on the central atom.

a) H2O sp3

b) PCl3 sp3

c) SF6 sp3d2 3) Draw and label a MO diagram for Li2

+ in its ground state. What is the bond order of the molecular ion Li2

+? Bond order is 0.5

2s 2s

σ*

σ

NAME:_____________________________ 4) a) Complete the following MO diagram for O2.

b) Using the above MO diagram determine bond orders for the following species O2

+, O2- or O2

2-? O2

+ bond order 2.5 O2

- bond order 1.5 O2

2- bond order 1.0 c) Which of the species O2

+, O2- or O2

2- has the shortest bond?

O2+has the shortest bond

d) Which of the species O2, S2 or O2

+ has the longest bond? S2 has the longest bond

e) Which of the following species are paramagnetic, O2

2-, O2-, O2, O2

+? O2

-, O2 and O2+ are paramagnetic

f) Which of the following species has the largest ionization energy, O2

2-, O2-, O2, O2

+? O2

+ has the largest ionization energy g) Which of the following has the largest ionization energy, O2 or O?

O has the largest ionization energy

2px, py, pz

2s

σ∗

σ

σ

σ∗

π

π∗

NAME:_____________________________ 5) For each of the following groups of molecules state which one is likely to have

the highest boiling point.

a) CCl4, GeCl4, SiCl4

b) PH3, NH3

c) HCl, HBr, HI, HF

d) H2S, H2Se, H2O

e) CH4, SiH4, GeH4

6) Assuming that the simplified MO energy level diagram for a diatomic molecule AB (given below) shows all the orbitals that play an important role in bonding answer the following questions.

a) Which of the atoms A or B is most electronegative?

B

b) What is the bond order for the molecule?

Bond order of 1.0 c) What happens to the molecule if one of the electrons in the sigma bonding

orbital is promoted to the sigma antibonding orbital giving an excited state with electron configuration σ1σ*1 ? (does the bond get weaker or stronger)

The bond gets weaker

A B

σ

σ*

NAME:_____________________________