IGCSE CHEMISTRY
SECTION 2 LESSON 2
Content
The iGCSE
Chemistry
course
Section 1 Principles of Chemistry
Section 2 Chemistry of the Elements
Section 3 Organic Chemistry
Section 4 Physical Chemistry
Section 5 Chemistry in Society
Content
Section 2
Chemistry
of the
Elements
a)
b)
c)
d)
e)
f)
g)
The Periodic Table
Group 1 Elements
Group 7 Elements
Oxygen and Oxides
Hydrogen and Water
Reactivity Series
Tests for ions and gases
Content
Lesson 2
c) Group 7
elements
d) Oxygen
and
oxides
c) Group 7 elements — chlorine, bromine and iodine
2.9 recall the colours and physical states of the elements at room temperature
2.10 make predictions about the properties of other halogens in this group
2.11 understand the difference between hydrogen chloride gas and hydrochloric acid
2.12 explain, in terms of dissociation, why hydrogen chloride is acidic in water but not in
methylbenzene
2.13 describe the relative reactivities of the elements in Group 7
2.14 describe experiments to demonstrate that a more reactive halogen will displace a
less reactive halogen from a solution of one of its salts
2.15 understand these displacement reactions as redox reactions.
d) Oxygen and oxides
2.16 recall the gases present in air and their approximate percentage by volume
2.17 explain how experiments involving the reactions of elements such as copper, iron
and phosphorus with air can be used to investigate the percentage by volume of oxygen in
air
2.18 describe the laboratory preparation of oxygen from hydrogen peroxide,using
manganese(IV) oxide as a catalyst
2.19 describe the reactions of magnesium, carbon and sulfur with oxygen in air, and the
acid-base character of the oxides produced
2.20 describe the laboratory preparation of carbon dioxide from calcium carbonate and
dilute hydrochloric acid
2.21 describe the formation of carbon dioxide from the thermal decomposition of metal
carbonates such as copper(II) carbonate
2.22 describe the properties of carbon dioxide, limited to its solubility and density
2.23 explain the use of carbon dioxide in carbonating drinks and in fire extinguishers, in
terms of its solubility and density
2.24 understand that carbon dioxide is a greenhouse gas and may contribute to climate
change.
Group 7 elements – chlorine, bromine
and iodine
The HALOGENS
Group 7 elements – chlorine, bromine
and iodine
The HALOGENS
All have seven
electrons in their
outer shell. To
become stable
they gain an
electron and carry
a charge of -1.
eg. Br- I- Cl-
Group 7 elements – chlorine, bromine
and iodine
The HALOGENS
Five non-metals
Group 7 elements – chlorine, bromine
and iodine
The HALOGENS
Five non-metals
Low melting and
boiling points,
increasing going
down the group
Group 7 elements – chlorine, bromine
and iodine
Gas
Gas
Liquid
Solid
Solid
All have coloured
vapours. Chlorine and
bromine are extremely
pungent (causing a
sharp or irritating
sensation)
Group 7 elements – chlorine, bromine
and iodine
The HALOGENS
are diatomic –
this means that
they go around
as paired atoms.
Group 7 elements – chlorine, bromine
and iodine
The HALOGENS
are diatomic –
this means that
they go around
as paired atoms.
Cl2
Br2
Group 7 elements – chlorine, bromine
and iodine
The HALOGENS
are diatomic –
this means that
they go around
as paired atoms.
Brittle and crumbly
when solid.
Cl2
Br2
Group 7 elements – chlorine, bromine
and iodine
Poor conductors
of heat and
electricity, even
when solid or
liquid.
Group 7 elements – chlorine, bromine
and iodine
Going down
the group, the
halogens
become less
reactive.
Poor conductors
of heat and
electricity, even
when solid or
liquid.
Group 7 elements – chlorine, bromine
and iodine
Halogens react with other non-metallic
elements, such as hydrogen, to form molecular
compounds:
Eg. hydrogen + chlorine  hydrogen chloride
H2(g) + Cl2(g) 
2HCl(g)
What’s the difference between
hydrogen chloride and hydrochloric acid
(they both have the same chemical
formula – HCl)
What’s the difference between
hydrogen chloride and hydrochloric acid
(they both have the same chemical
formula – HCl)
Hydrogen chloride is gaseous at
room temperature.
Hydrochloric acid is an aqueous
solution of hydrogen chloride –
i.e. dissolved in water.
Explain, in terms of
dissociation, why
hydrogen chloride is
acidic in water but not
in methylbenzene
Explain, in terms of
dissociation, why
hydrogen chloride is
acidic in water but not
in methylbenzene
?
Explain, in terms of
dissociation, why
hydrogen chloride is
acidic in water but not
in methylbenzene
?
“To separate, or split, into
smaller particles or ions”
Hydrogen
chloride?
Hydrogen
chloride?
Hydrogen chloride is a
covalent compound.
However, when dissolved in
water it dissociates to the
separate ions, H+ and CL-.
The H+ ion gives it acidic
properties.
Hydrogen
chloride?
When dissolved in an
organic solvent, such as
methylbenzene, hydrogen
chloride does not dissociate
into separate ions, so does
not show acidic properties.
Hydrogen
chloride?
When dissolved in an
organic solvent, such as
methylbenzene, hydrogen
chloride does not dissociate
into separate ions, so does
not show acidic properties.
Reactions of the halogens
Halogens react with metals to produce ionic salts
The halogen atom gains one electron to form the
halide ion which carries a charge of -1
eg.
Lithium + chlorine  lithium chloride
2Li(s) +
Cl2(g) 
2LiCl(s)
Reactions of the halogens
Halogens react with metals to produce ionic salts
The halogen atom gains one electron to form the
halide ion which carries a charge of -1
eg.
Lithium + chlorine  lithium chloride
2Li(s) +
Cl2(g) 
2LiCl(s)
YouTube video: comparing the four halogens
Reactions of the halogens
Summary:
Halogens + Hydrogen  hydrogen halides
HF, HCl, HBr, HI
All four are gases and very soluble in water
Halogens + Aluminium  Aluminium trihalides
AlF3, AlCl3, AlBr3, AlI3
All four are white solids
Describe experiments to
demonstrate that a more
reactive halogen will
displace a less reactive
halogen from a solution of
one of its salts
Describe experiments to
demonstrate that a more
reactive halogen will
displace a less reactive
halogen from a solution of
one of its salts
?
Describe experiments to
demonstrate that a more
reactive halogen will
displace a less reactive
halogen from a solution of
one of its salts
?
“In a displacement reaction a
more reactive element will
displace a less reactive element
from a compound.”
Halogen displacement
reactions
Remember that the reactivity of the
halogens decreases as we go down the
group, so Fluorine is the most reactive
halogen, and Astatine is the least
reactive – can you explain this trend in
terms of the number of electron
shells? (hint – think back to the Alkali
metals)
Halogen displacement
reactions
A more reactive halogen will displace a less reactive halogen
from an aqueous solution of its salt.
e.g. potassium iodide + chlorine  potassium chloride + iodine
2KI
+
Cl2

2KCl
+
I2
Halogen displacement
reactions
A more reactive halogen will displace a less reactive halogen
from an aqueous solution of its salt.
e.g. potassium iodide + chlorine  potassium chloride + iodine
2KI
+
Cl2
KI
solution
Displaced
iodine
Cl2

2KCl
+
I2
Halogen displacement
reactions
A more reactive halogen will displace a less reactive halogen
from an aqueous solution of its salt.
e.g. potassium iodide + chlorine  potassium chloride + iodine
2KI
+
Cl2

Displaced
iodine
+
I2
Potassium
chloride
KCl
Potassium
bromide
KBr
Potassium
Iodide
KI
Chlorine
Cl2
X
Bromine +
KCl
Iodine +
KCl
Bromine
Br2
No reaction
X
Iodine +
KBr
Iodine
I2
No reaction
No reaction
X
Cl2
KI
solution
2KCl
Understand these
displacement reactions as
redox reactions
Understand these
displacement reactions as
redox reactions
?
Understand these
displacement reactions as
redox reactions
?
“A redox reaction is where
both oxidation and reduction
occur.”
Redox
reaction?
Hydrogen
chloride?
The loss of electrons from
an atom is known as
oxidation.
The gain of electrons is
known as reduction.
Hydrogen
chloride?
Remember
OILRIG
Oxidation Is Loss = OIL
Reduction Is Gain = RIG
Hydrogen
chloride?
Remember
OILRIG
Oxidation Is Loss = OIL
Reduction Is Gain = RIG
Halogen displacement
reactions
e.g. potassium iodide + chlorine  potassium chloride + iodine
2KI
2K+ 2I-
+
Cl2

2KCl
2K+ 2Cl-
+
I2
Halogen displacement
reactions
e.g. potassium iodide + chlorine  potassium chloride + iodine
2KI
2K+ 2I-
+
Cl2

2KCl
2K+ 2Cl-
iodine loses 2e- (2I-  I2)
+
I2
Halogen displacement
reactions
e.g. potassium iodide + chlorine  potassium chloride + iodine
2KI
2K+ 2I-
+
Cl2

2KCl
2K+ 2Cl-
iodine loses 2e- (2I-  I2)
+
I2
Halogen displacement
reactions
e.g. potassium iodide + chlorine  potassium chloride + iodine
2KI
2K+ 2I-
+
Cl2

2KCl
2K+ 2Cl-
iodine loses 2e- (2I-  I2)
iodine has been oxidised
+
I2
Halogen displacement
reactions
e.g. potassium iodide + chlorine  potassium chloride + iodine
2KI
2K+ 2I-
+
Cl2

2KCl
2K+ 2Cl-
chlorine gains 2e- (Cl2  2Cl-)
+
I2
Halogen displacement
reactions
e.g. potassium iodide + chlorine  potassium chloride + iodine
2KI
2K+ 2I-
+
Cl2

2KCl
2K+ 2Cl-
chlorine gains 2e- (Cl2  2Cl-)
+
I2
Halogen displacement
reactions
e.g. potassium iodide + chlorine  potassium chloride + iodine
2KI
2K+ 2I-
+
Cl2

2KCl
2K+ 2Cl-
chlorine gains 2e- (Cl2  2Cl-)
chlorine has been reduced
+
I2
Halogen displacement
reactions
e.g. potassium iodide + chlorine  potassium chloride + iodine
2KI
2K+ 2I-
+
Cl2

2KCl
2K+ 2Cl-
+
I2
chlorine gains 2e- (Cl2  2Cl-)
chlorine has been reduced
In a REDOX reaction there is simultaneous
oxidation and reduction. In this reaction, iodine
has been oxidised, chlorine has been reduced.
Content
Lesson 2
c) Group 7
elements
d) Oxygen
and
oxides
c) Group 7 elements — chlorine, bromine and iodine
2.9 recall the colours and physical states of the elements at room temperature
2.10 make predictions about the properties of other halogens in this group
2.11 understand the difference between hydrogen chloride gas and hydrochloric acid
2.12 explain, in terms of dissociation, why hydrogen chloride is acidic in water but not in
methylbenzene
2.13 describe the relative reactivities of the elements in Group 7
2.14 describe experiments to demonstrate that a more reactive halogen will displace a
less reactive halogen from a solution of one of its salts
2.15 understand these displacement reactions as redox reactions.
d) Oxygen and oxides
2.16 recall the gases present in air and their approximate percentage by volume
2.17 explain how experiments involving the reactions of elements such as copper, iron
and phosphorus with air can be used to investigate the percentage by volume of oxygen in
air
2.18 describe the laboratory preparation of oxygen from hydrogen peroxide,using
manganese(IV) oxide as a catalyst
2.19 describe the reactions of magnesium, carbon and sulfur with oxygen in air, and the
acid-base character of the oxides produced
2.20 describe the laboratory preparation of carbon dioxide from calcium carbonate and
dilute hydrochloric acid
2.21 describe the formation of carbon dioxide from the thermal decomposition of metal
carbonates such as copper(II) carbonate
2.22 describe the properties of carbon dioxide, limited to its solubility and density
2.23 explain the use of carbon dioxide in carbonating drinks and in fire extinguishers, in
terms of its solubility and density
2.24 understand that carbon dioxide is a greenhouse gas and may contribute to climate
change.
Gases in the atmosphere
Gas
Percentage in dry
air
Nitrogen
78%
Oxygen
21%
Argon
<1%
Carbon dioxide
0.04%
The atmosphere also contains
tiny amounts of a few other
gases and also varying
amounts of water vapour.
explain how experiments
involving the reactions of
elements such as copper, iron
and phosphorus with air can be
used to investigate the
percentage by volume of
oxygen in air
explain how experiments
involving the reactions of
elements such as copper, iron
and phosphorus with air can be
used to investigate the
percentage by volume of
oxygen in air
explain how experiments
involving the reactions of
elements such as copper, iron
and phosphorus with air can be
used to investigate the
percentage by volume of
oxygen in air
We can use the reaction between
hot copper and oxygen to
determine the percentage of
oxygen in the atmosphere:
Copper + Oxygen  Copper oxide
2Cu + O2 
2CuO
Oxygen in the air
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/oil
s/changesrev5.shtml
explain how experiments
involving the reactions of
elements such as copper, iron
and phosphorus with air can be
used to investigate the
percentage by volume of
oxygen in air
Oxygen in the air
A measuring cylinder is
inverted into a beaker of
water. Previously, a piece of
iron wool had been placed
inside the measuring
cylinder. The apparatus is
left for a couple of days.
Oxygen in the air
As the iron wool rusts, it
absorbs oxygen from the air
inside the measuring
cylinder. When there is no
more change in the water
level, the height of water
inside the cylinder is
measured, and from this the
volume of oxygen in air can
be calculated.
explain how experiments
involving the reactions of
elements such as copper, iron
and phosphorus with air can be
used to investigate the
percentage by volume of
oxygen in air
Oxygen in the air
A bell jar is placed into a
trough of water. Coins are
placed for the bell jar to
rest on – this ensures that
water can move into the bell
jar. Water is poured in to
the bell jar to the zero level.
A piece of phosphorus is
placed on a watch glass
floating on the water
surface.
http://www.tutorvista.com/content/chemistry/chemistry-i/air-mixture/air-oxygen.php
Oxygen in the air
The phosphorus is lit using a
hot metal rod and the top is
placed on the bell jar
http://www.tutorvista.com/content/chemistry/chemistry-i/air-mixture/air-oxygen.php
Oxygen in the air
As the yellow phosphorus
starts to burn, the air space
inside the bell jar fills with
white fumes of phosphorus
oxide. This dissolves in the
water to form an acidic
solution.
http://www.tutorvista.com/content/chemistry/chemistry-i/air-mixture/air-oxygen.php
Oxygen in the air
As the phosphorus burns it
reacts with the oxygen in
the air in the bell jar, so the
water level rises as the
oxygen is used up. When the
reaction ends, the
percentage of oxygen in the
air can be calculated from
the change in the water
level.
http://www.tutorvista.com/content/chemistry/chemistry-i/air-mixture/air-oxygen.php
The preparation of oxygen
in the laboratory
Oxygen can be prepared in the laboratory
by the catalytic decomposition of
hydrogen peroxide solution:
2H2O2(aq)
MnO2
2H2O(l) + O2(g)
Manganese oxide is the catalyst used in
this reaction
The preparation of oxygen
in the laboratory
Hydrogen
peroxide
Oxygen
Manganese
oxide
End of Section 2 Lesson 2
In this lesson we have covered:
Group 7 elements – chlorine, bromine
and iodine.
Gases in the atmosphere
Oxygen in the air