CHEMISTRY 2.4
Credits: Four
INSTRUCTIONS
Answer ALL questions.
© New Zealand Institute of Chemistry 2006

2
You should aim to spend about 40 minutes on this assessment
(a) (i) Circle the Lewis structures (electron dot diagrams) below that are NOT drawn correctly.
H
H
N H
H H
C C
H H
H C H
O
H O H H
Cl
C Cl
H
A B C D E
(ii) Describe the error and draw the correct structures for two of the structures circled above.
Structure letter
Description of error
(b) Draw Lewis diagrams for the following molecules:
(i) CH
3
OH (ii) N
2
Correct structure
Turn over

3
(a) Name the shapes of each of the four molecules whose Lewis diagrams are shown below.
O S
O
O
O O O H
H
P H
H
H
C H
H
Shape________________ _______________ _________________ ______________
(b) Discus the factors that determine the shape of a molecule with reference to the examples above.
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(c) Describe a polar bond.
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(d) (i) Label the molecules, whose Lewis diagrams are drawn below, as polar or non polar.
O C O O O
Polarity _________________ _______________________
(ii) Give reasons for your answers.
O S O
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4
(a) (i) Choose a solid from the list provided which matches each of the descriptions in the table below. Each substance can be used only once.
List: SiO
2
, NaCl, I
2
, Cu
Description:
1 A solid with a high melting point that conducts electricity.
2 A solid with a low melting point that does not conduct electricity.
3 A solid with a high melting point that dissolves in water.
4 A solid with a high melting point that does not conduct electricity.
Example of solid
(ii) Justify your answer to 1 and 2 above in terms of the structure and bonding within the solids.
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(iii) Explain why the solid chosen for 3 dissolves in water.
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(b) Discuss, in terms of structure and bonding within the compound, under what conditions lithium chloride would conduct electricity, and when it would not.
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Turn over
End of assessment