The halogens

1.

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2.

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3. Group 7 – the halogens

The elements in group 7 of the periodic table, on the right,
are called the halogens.
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F
fluorine
Cl
chlorine
Br
bromine
I
iodine
At
astatine
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4. 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 things, including
bacteria.
They are also never found free in nature because of their
reactivity – 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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5. What is the electron structure of the halogens?

All halogens have seven electrons in their outer shell.
This means that:
fluorine
They can easily obtain a
2,7
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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chlorine
2,8,7
bromine
2,8,8,7
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6. How do halogen molecules exist?

All halogen atoms require one more 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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7.

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8. What are the general 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 red-brown
is blue-black.
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9. What is the physical state of the halogens?

The melting and boiling points of the halogens increase
down the group, as the molecules become bigger.
Halogen
Relative
size
Melting
point (°C)
Boiling
point (°C)
State
-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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10. Halogen vapours

Bromine and iodine are not gaseous, but have low boiling
points. This means that they produce vapour at relatively
low temperature. They are volatile.
Bromine produces some
red-brown vapour, seen
here above the liquid
bromine in the jar.
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When iodine is heated gently, it
changes directly from a solid to a
gas without first becoming a liquid.
This is called sublimation.
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11.

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12. How do the halogens react with metals?

The reactivity of halogens means that they readily react with
most metals.
Halogens need to gain electrons for a full electron shell and
metals need to lose electrons for a full electron shell.
This means that halogens and metals react to form ionic
compounds.
These are metal halides, which are a type of salt.
nickel (II) chloride
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copper (II) chloride
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13. What are halides?

When halogens react with another substance, they become
negative ions, as they are gaining an extra electron.
When this happens, they are called halides.
The name of each of the halogens changes slightly once
it has reacted – instead of ending with ‘–ine’, they end
with ‘-ide’.
Halogen
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reaction
Halide
(F)
fluoride (F-)
(Cl)
chloride (Cl-)
(Br)
bromide (Br-)
(I)
iodide (I-)
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14. Equations of halogens and iron

When a halogen reacts with iron it forms an iron halide:
halogen
+
iron
iron (III) halide
The word and chemical equations for the reaction between
chlorine and iron are:
iron (III)
chlorine + iron
chloride
3Cl2 (g)
+ 2Fe (s)
2FeCl3 (s)
What would the equation be for the reaction that forms
iron (III) bromide?
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bromine
+ iron
iron (III)
bromide
3Br2 (g)
+ 2Fe (s)
2FeBr3 (s)
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15. How do the halogens react with non-metals?

Halogens also react with non-metals.
For example, halogens react with hydrogen to create
hydrogen halides.
H
hydrogen
+
Cl
chlorine
H
Cl
hydrogen chloride
Unlike their reactions with metals, halogens share electrons
with non-metals, and so react to form covalent compounds.
All hydrogen halides are gases. They dissolve easily in
water and become strong acids.
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16. 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
F2 (aq)
+ 2NaCl (aq)
2NaF (aq)
+
Cl2 (aq)
A more reactive halogen will always displace a less reactive
halide from its compounds in solution.
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17. Displacement of halogens

Why will a halogen always displace a less reactive halogen?
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18. Displacement theory

If a metal halide is mixed with a more reactive halogen,
the extra electron will be transferred from the less reactive
to the more reactive halogen.
--
+
chlorine
chloride
sodium
Na
Cl
fluorine
fluoride
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F
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19. Displacement reactions: summary

The reactions between solutions of halogens and metal
halides (salts) can be summarised in a table:
salt (aq) potassium
chloride
halogen
potassium
bromide
potassium
iodide
chlorine
2KCl + Br2
2KCl + I2
bromine
no reaction
iodine
no reaction
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2KBr + I2
no reaction
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20.

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21. What are the uses of halogens?

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22.

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