Hong Kong Chinese Women’s Club College
Chemistry
Form 4
Bonding-Ex1
Answer in complete sentences wherever appropriate.
1.
a)
The table below lists some physical properties for potassium chloride and
tetrachloromethane, CCl4.
Melting point /oC
Solubility in water at
25o C / g per 100 cm3
potassium chloride
776
32
tetrachloromethane
- 23
Insoluble
i) Explain the difference in melting point between potassium chloride and
tetrachloromethane in terms of the nature of forces between particles.
ii) Draw the electronic structures of potassium chloride and tetrachloromethane,
indicating the arrangement of electrons in the outermost shells only.
iii) 32 g of potassium chloride, 32 g of tetrachloromethane and 100 cm3 of water
are shaken together in a stoppered flask at 25oC and then allowed to settle.
After a few minutes, what would be observed ?
b)
The various properties of the substances are given in the following table :
Substances
Silicon(IV) oxide
SiO2
Sulphur dioxide
SO2
Calcium oxide
CaO
Glucose
C6H12O6
Copper, Cu
Melting point
1700oC
Action with water
Insoluble
Electrical conductivity
Non-conductor
- 75oC
Non-conductor
2600oC
Reacts with water
and dissolves
Slightly soluble
146oC
Soluble
Non-conductor
1083oC
Insoluble
Conducts well without
any decomposition
Electrolysis occurs
i) Classify the above substances into those having the following structures :
A) giant ionic structure,
B) giant covalent structure, and
C) simple molecular structure.
State reasons for your choice.
ii) Briefly explain why solid copper can conduct electricity at room temperature.
iii) Briefly explain molten calcium oxide can conduct electricity.
Hong Kong Chinese Women’s Club College
Chemistry
Form 4
Bonding-Ex1
Suggested Answers
1.
a)
i)
Potassium chloride, an ionic compound, has high melting point as their opposite
charged ions are held strongly by electrostatic forces. A large amount of energy is
needed to melt the ionic compound - potassium chloride. Tetrachloromethane is a
covalent compound which molecules are held by weak van der Waals’ forces. It thus
has a low melting point.
ii) potassium chloride
tetrachloromethane
Cl
Cl
+
K
C
Cl
Cl
Cl
iii) There are two separate (immiscible) layers. Tetrachloromethane forms the bottom oily
layer. Potassium chloride dissolves completely in the upper colourless aqueous layer.
b) i)
A) giant ionic structure : calcium oxide
Calcium oxide, an ionic compound with high melting point, and cannot conduct
electricity in molten state.
B) giant covalent structure : silicon (IV) oxide.
Silicon(IV) oxide is in giant covalent lattice as it has high melting point and
cannot conduct electricity either in solid or molten state.
C) Simple molecular structure : glucose and sulphur dioxide
They have low melting points. They cannot conduct electricity in molten state.
ii) Copper, a metal, can conduct electricity as it has mobile electrons.
iii) Solid calcium oxide does not have any free / mobile ions . Ions are fixed / held
strongly by electrostatic forces and cannot move. When the ionic compound melts,
ions become mobile and can conduct electric current.