UNIT8:TRENDS OF CHEMICAL PROPERTIES OF GROUP 13 ELEMENTS AND THEIR COMPOUNDS
UNIT 8: TRENDS OF CHEMICAL PROPERTIES
OF GROUP 13 ELEMENTS AND THEIR
COMPOUNDS
Key unit competence: Compare and contrast the chemical properties of the Group 13
elements and their compounds, in relation to their position in the Periodic Table.
Learning objectives
By the end of this unit, students should be able to:
• State the physical properties of Group 13 elements
• Explain the reactivity of Group 13 elements with oxygen, water, halogens,
dilute acids and sodium hydroxide
• Describe the properties of oxides, hydroxides and chlorides of Group 13
elements
• State the uses of Group 13 elements and their compounds
• Compare and contrast the reactivity of Group 13 elements with oxygen,
water, halogens, dilute acids and sodium hydroxides
• Perform experiments to show the solubility of Group 13 compounds
• Practically illustrate the amphoteric properties of aluminium oxides and
hydoxides
• Identify the anomalous properties of boron and its compounds
• Perform chemical tests for the presence of aliminium ion in the solution.
1. Consider the following elements: boron (z=5), aluminium (z=13), gallium (z=31),
indium (z=49), thallium (z=81)
(a)Write the electronic configuration of each element in term of s,p,d,f orbitals.
(b) State the period and the block to which each element belongs.
2. Draw diagram to show metallic bond in aluminium metal.
3. Cite one known application of an element of Group 13 in our everyday life4. Explain why aluminium is a better conductor of electricity than sodium
8.1. Physical properties of group 13 elements
Activity 8.1
In groups learners make research in library or on internet, discuss and explain why
a. Group 13 elements have higher melting point than group 1and 2 elements.
b. Boron has higher ionization energy than other element of the same group.
With the exception of boron, group 13 elements are metals. Boron is a non-metal
element with high melting point and low density.
Aluminium is a metal element and has a low density, it is a good conductor of heat
and electricity, shiny, malleable, ductile and it has higher melting point than groups
1and 2 metals due to strong metallic bond resulting from 3 valency electrons
involved in making metallic bonding in aluminium metal.
In small atoms electrons are held tightly and are difficult to remove, while in large
ones they are less tightly held since they are far away from the nucleus and are easy
to remove so that the ionization energy decreases down the group as the atomic
radius increases.
The greater the forces of attraction and hence the boiling point and melting pointdecrease down the group as the atomic radius increases.
8.2. Reactions of aluminium
8.2.1. Reaction of aluminium with oxygen
8.2.3. Reaction with alkalis
Activity 8.2 (d):
Reaction of aluminium with concentrated NaOH solution
Experiment
Learners perform experiments to investigate the reaction of aluminium with
NaOH solution
Apparatuses: thermometer, pyrex beaker,stirrer
Chemicals: aluminium powder,40% sodium hydroxide solution
Procedure:
• Prepare 40% of sodium hydroxide by mixing 60cm3
of water with 40g of
sodium hydroxide
• Take 0.5 g of aluminium powder into a pyrex beaker
• Pour the solution of sodium hydroxide in the pyrex beaker containing
aluminium powder and allow the reaction to proceed for about 5 minutes.• Use thermometer to record the temperature during the process
compounds; and only p electron will participate, hence the oxidation state +1.
For lighter members such B and Al the s and p valency electrons, having almost the
same energy, are always available and used at the same time to form compoundswhere they are in oxidation state +3.
8.4. Anomalous properties of boron
Activity 8.4
In groups learners make research on internet and in library, discuss and explain
the following statement:
a) Boron is a bad conductor of electricity
b) Boron has higher boiling and melting points than other member of the groupc) Boron oxide is an acidic oxide
Checking up 8.4
a) What is the cause of abnormal behavior of boronb) State any anomalous properties of boron
8.6. Uses of some group 13 elements
Activity 8.6
a. Teacher brainstorms learners and ask them to talk about different applications
of aluminium and its compounds in daily life.
b. Make research in libraries / internet and discuss about the use of aluminium,boron
and gallium and make presentations of your findings.
Aluminium
Aluminium is aboundant in the Earth’s crust and its applications are many. It is used
in:
• making cooking utensils: this is because of its bright appearance and
lightness, resistance to corrosion, and its thermal conductivity
• window frames or doors in buildings and houses
• overhead high tension cables for distribution of electricity: this is because
of its low density and very good electrical conductivity.
• alloys (e.g. Al and Mg) for the construction of airplanes and small boats due
to its lightness, malleability and higher tensile strength in the alloy.
• Being completely resistant to corrosion it is ideal for packaging food
• The insulating property of aluminium arises from its ability to reflect radiant
heat; this property is used in firefighters’ wear to reflect the heat from the
fire and keep them cool.
• The polished surface of aluminium is used in the reflectors of car headlights
• Aluminium is a component of clay (ibumba), mainly hydrous sulphate of
aluminium, used in the traditional production manufacture of clay pots
(ibibindi/ inkono).
• Clay is also one of the basic raw materials in the production of Cement
Boron
Applications of boron are found in:
• control rods to keep nuclear reactions in balance and avoid explosion; boron
absorbs excess neutrons preventing them from bombarding too many
uranium atoms which may result into explosion (fuel of nuclear reactors)
• the manufacture of hard boron steel
• as an additive to semiconductors silicon and germanium
• the manufacture of borosilicate glass used in vacuum flasks and test tubes
(a) Write a chemical equation to represent the reaction.
(b) Why is it necessary to dry the chlorine?
(c) What is the purpose of the soda lime?
(d) Aluminium chloride is dissolved in water. Write the equation for the reaction that takes place
2. (a) With reference to aluminium oxide, explain the term amphoteric oxide. Write
equations to illustrate.
(b) Explain with chemical equations why aluminium utensils are not washed in
strong alkaline solutions.
(c) Aluminium resists to corrosion. Comment and explain that popular saying.
3. If you need to prepare aluminium hydroxide, why is it better to add a solution
of ammonia to a solution of aluminium salt, rather than to add a solution of
sodium hydroxide.
4. How does gallium react with:
(a) hydrochloric acid
(b) Sodium hydroxide
5. Explain why aluminium is suitable for the following uses:
(a) Manufacture of window frames
(b)Electrical wiring
(c)Packaging food
(d)Suits for firefighters
6. Water is suspected to contain calcium and aluminium ions. State a chemical test
that should be used to confirm the presence of the suspected ions. State the
reagent, observations and related chemical equation if any