Page 16 - Spotlight A+ Form 4 & 5 Chemistry KSSM

Form
4
Chemistry Chapter 5 Chemical Bond

Conclusion: 2. A spatula of naphthalene, C H powder is
10 8
The hypothesis is accepted. Magnesium chloride, placed in another test tube.
MgCl is an ionic compound which is soluble in 3. The two test tubes are heated in a beaker
2
water but insoluble in organic solvents. Napthalene, containing water as shown in Figure 5.38.
C H is a covalent compound which is insoluble in 4. The changes in the physical states of the
10 8
water but soluble in organic solvents. compounds are observed and recorded.
Discussion: Results:
1. Magnesium chloride, MgCl dissociates in Table 5.8
2
water to produce free moving magnesium ions
Mg and chloride ions, Cl . Compound Observation Inference
–
2+
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2. Naphthalene, C H consists of neutral
10 8 Magnesium No change Magnesium chloride,
molecules which cannot dissociate in water.
chloride, MgCl has a high
2
C Melting and boiling points MgCl melting point.
2
Hypothesis:
Ionic compounds have high melting and boiling Naphthalene, It melts Naphthalene, C H
8
10
points while covalent compounds have low melting C H 8 rapidly. has a low melting
10
and boiling points. point.
Variables: Conclusion:
(a) Manipulated: Type of compound, magnesium The hypothesis is accepted. Magnesium chloride,
chloride, MgCl and napthalene, C H MgCl is an ionic compound and naphthalene,
2 10 8 2
(b) Responding: Boiling point C H is a covalent compound. Magnesium
8
10
(c) Fixed: Quantity of compound chloride, MgCl has a higher melting point than
2
naphthalene, C H .
Procedure: 10 8
Discussion:
1. Magnesium chloride, MgCl consists of positive
2
2+
–
ions, Mg and negative ions, Cl . Mg ions
2+
Water, H O
–
2 and Cl ions are attracted together by strong
Magnesium
Naphthalene,
chloride, MgCl electrostatic forces. A lot of heat energy is
2 C H
10 8 required to overcome the strong electrostatic
CHAP. Heat attraction forces. Therefore, the melting point CHAP.
5 of magnesium chloride, MgCl , is high. 5
2
2. Naphthalene, C H consists of molecules which
10 8
Figure 5.38 are attracted by weak Van der Waals attraction
forces. As a result, less heat energy is required
1. A spatula of magnesium chloride, MgCl to overcome the weak Van der Waals attraction
2
powder is placed in a test tube. forces.
Structure of Ionic Compounds and Covalent Compounds
1. Ionic compounds consist of positive ions of
metals and negative ions of non-metals. The
positive ions and negative ions attract each other In the actual structure, ions are packed together
to form a rigid three-dimensional structure closely as shown in Figure 5.40. Figure 5.39 just
which is called lattice. Each ion in the lattice to make the structure easy to see.
structure is surrounded by other ions of opposite
charges.
Example:
Sodium chloride, NaCl consists of sodium ions,
Na and chloride ions, Cl .
–
+ Figure 5.40
Na
–
Cl 2. The arrangement shown in Figure 5.39 does not
exist separately on its own. It extends throughout
the crystal, involving millions of ions. This
structure is known as giant ionic lattice.
Figure 5.39 The lattice structure of NaCl
134 5.7.1