OCR AS Chemistry F332: Group 7

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Group 7
The Halogens
The halogens are the elements in group 7 of the periodic table.
All halogen atoms have seven electrons in the outer shell.
The halogens are the most reactive group of non-metals, and none of them is found
naturally in the element form.
They are all found in compounds, often as halide ions.
All the halogen elements occur as diatomic non-polar molecules ­ for example F2 and Br2.
As the atoms become larger as you go down the group, they become less electronegative.
Physical properties of the halogens
Fluorine Chlorine Bromine Iodine
Appearance and Pale yellow gas Green gas Dark red liquid Shiny black solid
state at room
temperature
Melting point/K 53 172 266 387
Boiling point/K 83 239 332 457
Volatility Gas Gas Liquid quickly Sublimes on
forms brown warming to give
gas on warming a purple vapour
Solubility in Reacts with Slightly soluble Slightly soluble Barely soluble,
water water to give pale to give a red gives a brown
green solution solution solution
Solubility in Soluble Soluble to give a Soluble to give a Soluble to give a
organic solvents pale green red solution violet solution
(e.g. hexane) solution

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Bonds between Molecules
The intramolecular bonds are covalent.
The intermolecular bonds are instantaneous dipole ­ induced dipole.
As the size of the molecule and number of electrons increases, so does the strength of the
intermolecular bonds.
This explains why the physical state of halogens changes from gas to liquid to solid as you go
down the group.
Chemical properties of the halogens
The halogens are a group of reactive elements.
They tend to remove electrons from other elements ­ they are oxidising agents.…read more

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Overall, this means that fluorine is the most reactive member of the halogen group, and
reactivity decreases as the group is descended.…read more

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Halogens as Oxidising Agents
The halogens are the most reactive non-metals in the periodic table and are strong
oxidising agents removing electrons in reactions.
Oxidation is loss of electrons.
The oxidising power of a halogen is a measure of the strength with which a halogen atom is
able to attract and capture an electron to form a halide ion.
In redox reactions each halogen atom gains one electron into a p sub-shell to form a halide
ion with a 1- charge.
e.g.…read more

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Redox Reactions of the Halogens
Redox reactions can show that the halogens become less able to form halide ions down the
group.
You can show the decrease in reactivity using redox reactions of:
Aqueous solutions of halide ions Cl- (aq), Br- (aq) and I- (aq)
Aqueous solutions of halogens Cl2 (aq), Br2 (aq) and I2 (aq)
Each halogen is mixed with aqueous solutions of the different halides.
A more-reactive halogen will oxidise and displace a halide of a less-reactive halogen.…read more

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Electrolysis of Halide Solutions
When you electrolyse aqueous solutions containing iodide or bromide ions, the halogen
element is released at the anode (the positive electrode).
The halide ions lose electrons to the electrode and are oxidised to atoms, which combine to
form molecules.…read more

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Storing and Transporting Halogens
The more reactive halogens can be quite dangerous.
They must be kept away from flammable materials as they are oxidising agents and
increase fire risks.
They are also toxic and corrosive, so must be kept away from skin and eyes.
Fluorine
Fluorine is the most reactive halogen, and the most hazardous.
Wherever possible, it's produced where it will be used ­ to avoid transporting or storing it.…read more

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Uses of Halogens
Although they are hazardous, the halogens are widely used because they are needed to
make many useful compounds.…read more

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