Group 7 redox reactions

Physical properties and trends of the halogens; oxidising power of the halogens; disproportionation reactions.

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Group 7 redox reactions
Physical properties
The halogens have the following physical properties:
They have low melting and boiling points
They exist as diatomic molecules
As you descend the group, the number of electrons increases, leading to
an increase in van der Waals forces between molecules, which lead to the
following trends being seen:
The boiling points of the halogens increases down the group
The physical states of the halogen at RTP goes from gas => liquid =>
solid as you descend the group
Electron configuration
The elements in group 7 have 7 electrons in their outer shell
Each group 7 element has:
One electron fewer than the noble gases
An outer p shell containing five electrons
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.
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
In redox reactions, each halogen atom gains one reaction into a p sub-shell
to form a halide ion with a 1- charge. Example:
½ Cl2 (g) + e- => Cl- (g)
The halogens become less reactive as you descend the group as their
oxidising power decreases.
As halogens gain an electron in their reactions, reactivity decreases down
the group because:
The atomic radius increases
The electron shielding increases
The ability to gain an electron into the p sub-shell decreases to form
a halide ion

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Redox reactions of the halogen
Redox reactions can show that the halogens are less able to form halide
ions as you descend the group.
This trend can be shown by reacting aqueous solutions of halide ions with
aqueous solutions of halogens.
Each halogen is mixed with aqueous solutions of the different halides.
More reactive halogens will oxidise and displace halides of less reactive
This is a displacement reaction
Any change in colour will show if a redox reaction has taken place.…read more

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Chlorine is only slightly soluble in water and has a mild bleaching action.
Household bleach is formed when dilute aqueous NaOH and Cl2 react
together at room temperature.
This is also a Disproportionation reaction in which chlorine has been both
reduced and oxidised.…read more


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