Page 14 - Spotlight A+ Form 4 & 5 Chemistry KSSM

Form
4
Chemistry Chapter 5 Chemical Bond
Positive ion 5. Less heat energy is required to overcome the
Negative ion weak Van der Waals attraction forces. This
explains why covalent compounds have low
A lot of heat energy is melting and boiling points.
required to break the strong
electrostatic forces during 6. Covalent compounds usually exist as volatile
melting or boiling. liquids at room temperature.

Figure 5.34 Oppositely-charged ions in an ionic Try Question 1 in Formative Zone 5.7
compound are held together by strong
electrostatic attraction forces Table 5.5 Comparison between properties
of ionic and covalent compounds
2. A lot of heat energy is required to overcome
the strong electrostatic forces. This explains Properties Ionic Covalent
why ionic compounds have higher melting and compounds compounds
boiling points.
3. Ionic compounds are usually non-volatile Melting point High Low
solids at room temperature. and boiling
4. On the other hand, covalent compounds (with point
simple molecular structures) consist of neutral
molecules which are held together by Van der Electrical Conduct Do not conduct
Waals attraction forces. conductivity electricity in electricity in any
aqueous or states
Less heat energy is molten state
required to break the
weak Van der Waals
attraction forces Solubility Usually dissolve Usually dissolve in
during melting in water but do organic solvents such
Molecules or boiling.
not dissolve in as benzene but do not
Figure 5.35 Molecules in a covalent compound are held organic solvents dissolve in water
together by weak Van der Waals attraction forces

CHAP. ©PAN ASIA PUBLICATIONS CHAP.
5 5.1 5

Aim: Variables:
To compare the properties of ionic compounds (a) Manipulated: Type of compound
and covalent compounds. (b) Responding: Electrical conductivity
(c) Fixed: Carbon electrode
Problem statement:
What are the differences between properties of Procedure:
ionic compounds and covalent compounds?
Batteries Bulb Switch
Materials:
Magnesium chloride, MgCI , cyclohexane, C H
2 6 12
naphthalene, C H , distilled water, solid lead (II)
10 8 Carbon electrodes
bromide, PbBr
2
Lead(II) bromide, PbBr
Apparatus: 2
Test tubes, crucible, 10 cm measuring cylinder,
3
3
spatula, glass rod, 250 cm beaker, Bunsen burner,
wire gauze, tripod stand, carbon electrodes,
pipe clay triangle, battery, connecting wire with
crocodile clip, light bulb, switch Figure 5.36
A Electrical conductivity 1. A crucible is filled with lead(II) bromide, PbBr
2
Hypothesis: powder until it is half full.
Ionic compounds can conduct electricity in the 2. The apparatus is set up as shown in Figure
molten state but not in the solid state while 5.36.
covalent compounds do not conduct electricity in 3. The switch is turned on. The observation on
both states. the light bulb is recorded.

132 5.7.1