The Structure of Compounds

1. Consider the following substances:

   lead (II) bromide	lithium chloride	potassium iodide	sugar	hydrogen chloride	sulfur	copper

   • (a) Name the substance(s) that conduct electricity in the solid state. Explain.
   • (b) Name the substance(s) that conduct electricity both in the liquid state (i.e. when molten) and in aqueous solution. Explain.
   • (c) Name the substance(s) that do not conduct electricity themselves but form conducting liquids when dissolved in water. Explain.
   • (d) Name the substance(s) that do not conduct electricity. Explain.
2. Take a look at the properties of two bromine-containing compounds:
   1. hydrogen bromide, HBr,
   2. sodium bromide, NaBr.

   	Electrical Conductivity
   	Solid	Liquid	Aqueous Solution
   HBr	very low	very low	high
   NaBr	very low	high	high

   • (a) The difference in conductivities of these two compounds can be explained in terms of bonding. Describe the bonding in these two compounds.
   • (b) Explain the difference in electrical conductivity for NaBr in the solid state and in the liquid state.
   • (c) Explain the difference in electrical conductivity for HBr in aqueous solution and in the solid and liquid states.
   • (d) Write the chemical equation which describes the behaviour of HBr in aqueous solution.
3. Describe the trends in the electronegativities of the elements across a row and down a column of the periodic table.
4. Which element in the periodic table has the largest electronegativity?
5. Which element in the periodic table has the smallest electronegativity?
6. Arrange the following elements in order of decreasing electronegativity.
   • (a) Mg, Al, P, O, K
   • (b) C, Si, Ga, O, Ca
   • (b) P, As, Cl, S, Mg
7. Explain why CO₂ has no dipole moment.
8. Explain why H₂O is a polar molecule.
9. Explain why I₂ is a nonpolar covalent compound.

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Chemistry Department
British Columbia Institute of Technology, Burnaby, B.C. Canada.
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