LEVY MWANAWASA MEDICAL UNIVERSITY
INSTITUTE OF BASIC AND BIOMEDICAL SCIENCES
DEPARTMENT OF NATURAL SCIENCES
2020/2021 ACCADEMIC YEAR
CHM101: FOUNDATION CHEMISTRY TUTORIAL SHEET/ASSIGNMENT 4
INSTRUCTIONS
Submit question 3, 4, 5, 6, 9, 10 and 11 on Tuesday 14th September 2021, 12:00 hours
1. Describe the general trends in electronegativities of the elements in the periodic table
both across a period and down a column.
2. What is a resonance description of a molecule? Why is this concept required if we wish
to retain Lewis formulas as a description of the electron structure of molecules?
3. For each of the following, write the electron configuration and Lewis symbol:
(a) As (b) As3+ (c) Se (d) Se2
(b) Arrange the following in order of increasing ionic radius: Cl, Na+, and S2. Explain
this order.
4. Decide which of the following bonds is least polar on the basis of electronegativities of
atoms: HN, SiBr, NCl. Indicate the partial charges for the bonds, using the symbols
+ and .
5. Write resonance descriptions for the following: (a) NO2 (b) FNO2
6. Write Lewis formulas for the following:
(a) BeCl2 (b) BCl3 (c) BrF5
7. Write a Lewis formula for each of the following, assuming that the octet rule holds for
the atoms. Then obtain the formal charges of the atoms.
(a) O3 (b) CO (c) HNO3
8. Which of the following two compounds has the shorter carbon–oxygen bond?
9. Predict the shape or geometry of the following molecules, using the VSEPR model.
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(a) SiF4 (b) SF2 (c) COF2 (d) PCl3
10. Predict the geometry of the following ions, using the electron-pair repulsion model.
(a) ClO3 (b) PO43 (c) SCN (d) H3O+
11. Use partial orbital diagrams to describe how the mixing of atomic orbitals on the central
atoms leads to hybrid orbitals in each of the following molecules.
(a) CH3OH
(b) SF4
12. Describe the types of bonds and orbitals in acetone, (CH3)2CO.
13. Use MO diagrams to predict whether H2+ and H2- can exist. Determine their bond orders
and electron configurations.
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