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Group 7, the Halogens (10.1: The Halogens (Physical Properties (F - Pale…
Group 7, the Halogens
10.1: The Halogens
Physical Properties
F - Pale yellow gas
Cl - Greenish gas
Br - Red-brown liquid
I - Black solid
All have a 'swimming bath' smell
F-F bond is weak compared with the rest of the halogens. Small size of atom leads to repulsion between non-bonding electrons as they are so close
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Electrons get further from nucleus so shielding increases. These factors more important that increasing nuclear charge so electronegativity decreases down a group
Melting and Boiling points increase down the group as larger atoms have more electrons so van der waals forces are stronger. The lower the BP, the more volatile the element, chlorine (gas) is more volatile than iodine (solid)
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10.4: Uses of Chlorine
Reaction with Water
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Here the O number of one Cl increases from 0 to +1 and the other decreases from 0 to -1. This is called disproportionation (when one atom of the same element increases and the other decreases)
This takes place when Cl is used to purify water for drinking or swimming to prevent diseases. Chloric(I) acid kills bacteria by oxidation and is in bleach.
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An alternative is solid sodium which reacts with water to for Chloric(I) acid in a reversible reaction.
In alkaline solution, the equilibrium moves to the left and HClO is removed as ClO- ions.
To prevent this happening, swimming pools need to be kept slightly acidic but never gets acidic enough to corrode metal or affect swimmers
Reactions with alkali: Reacts with cold dilute NaOH to form sodium chlorate(I) which is an oxidising agent and in household bleach. This is also a disproportionate reaction
Other halogens behave similarly