Group 7 – Halogens
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What are you
aiming for?
Bronze, Silver
or Gold?
Self- Assessment Targets
I can describe the properties of group 7 (halogens).
I can test for the reactivity of halogens using iron wool.
I can explain the displacement reactions of halogens.
How do alkali metals react with water?
All of the alkali metals react vigorously with water.
The reaction becomes more vigorous as you descend
the group.
It is an exothermic reaction as it releases a lot of heat.
The reaction produces a gas that ignites a lighted splint with
a squeaky pop. What is this gas?
When green universal indicator
is added to the reaction mixture,
it turns purple.
What does this tell you about
the products of this reaction?
https://www.youtube.com/watch
?v=DxzFf1ku6cE
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How do alkali metals react with water?
How will rubidium and caesium react with water?
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Starter:
•Watch the following video
https://www.youtube.com/watch?v=J7b2aBKa6-U
then:
• Explain why halogens exist as
diatomic molecules.
Group 7 – the halogens
The elements in group 7 of the periodic table are called
the halogens.
F
fluorine
Cl
chlorine
Br
bromine
I
At
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iodine
astatine
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Why are they called the ‘halogens’?
Halogens are very reactive non-metals.
They are all toxic or harmful
because they are so reactive.
Before antiseptics, iodine was
used to clean wounds, as it is
harmful to all organisms,
including bacteria.
Halogens are never found free in nature because of their
reactivity. Instead, they are found as compounds with metals.
These halogen-metal compounds are salts, which give
halogens their name – ‘halo-gen’ means ‘salt-former’.
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Electron structure
All halogens have seven electrons in their outer shell.
This means that:
 They can easily obtain a
full outer shell by gaining
one electron.
 They all gain an electron
in reactions to form
negative ions with a -1
charge.
 They have similar
chemical properties.
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fluorine
2,7
chlorine
2,8,7
bromine
2,8,8,7
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How do halogen molecules exist?
All halogen atoms require one additional electron to obtain
a full outer shell and become stable.
Each atom can achieve this by sharing one electron with
another atom to form a single covalent bond.
F
+
F

F
F
This means that all halogens exist as diatomic molecules:
F2, Cl2, Br2 and I2.
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What are the properties of the halogens?
All the halogens are:
 non-metals and so do not conduct electricity
 brittle and crumbly when solid
 poisonous and smelly.
They become darker in colour down the group:
is pale yellow
is green-yellow
is dark orange
is dark grey.
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Predicting properties
The melting and boiling points of the halogens increase
down the group as the molecules become bigger.
Halogen
Relative
size
Melting
point (°C)
Boiling State (room
point (°C) temperature)
-220
-118
gas
-101
-34
gas
-7
59
liquid
114
184
solid
What is the state of each halogen at room temperature?
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How do the halogens react with metals?
The electron structure of halogens means that they react
vigorously with group 1 alkali metals.
Halogens need to gain one electron for a full outer shell and
alkali metals need to lose one electron for a full outer shell.
This means that halogens and
alkali metals react to form ionic
compounds.
These are metal halides,
which are a type of salt.
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What are halides?
When halogen atoms react with other substances, they form
negative ions by gaining an electron.
When this happens, they are called halides.
The name of each of the halogens changes once it has
reacted. Instead of ending with ‘–ine’, it ends with ‘–ide’.
Halogen
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Halide
(F)
fluoride (F-)
(Cl)
chloride (Cl-)
(Br)
bromide (Br-)
(I)
iodide (I-)
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Halogen reaction with iron wool
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What is the reactivity of the halogens?
decrease in reactivity
The iron wool experiment shows that the reactivity of
halogens decreases down the group.
Halogen
Reaction with iron wool
Iron wool burns and glows brightly.
Iron wool glows, but less brightly than
with chlorine.
Iron wool has a very slight glow.
Astatine is the halogen that appears directly below iodine
in the periodic table. How do you think astatine would react
with iron wool?
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Electron structure and reactivity
The reactivity of halogens decreases going down the
group. What is the reason for this?
 This means that the outer shell gets
further away from the nucleus and
is shielded by more electron shells.
 The further the outer shell is
from the positive attraction of the
nucleus, the harder it is to attract
another electron to complete the
outer shell.
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F
Cl
Br
decrease in reactivity
 The atoms of each element get
larger going down the group.
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Displacement of halogens
If a halogen is added to a solution of a compound containing
a less reactive halogen, it will react with the compound and
form a new one.
This is called displacement.
fluorine
+
sodium
chloride
sodium
fluoride
+
chlorine
A more reactive halogen will always displace a less reactive
halide from its compounds in solution.
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Displacement of halogens
Why will a halogen always displace a less reactive halogen?
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What are the uses of halogens?
How many everyday uses of halogens can you see below?
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