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Group 7, the Halogens
Fl pale yellow gas
Cl greenish gas
Br red brown liquid
I black solid
`Swimming bath smell'
F F bond is weak as the small size of the atom leads to repulsion between the non bonding
SIZE OF ATOMS
Get bigger down the group as the elements going down have an extra filled main level of electrons.
Electronegativity is the measure of ability of an atom to attract electrons, or an electron density,
towards itself within a covalent bond.
It depends on the attraction between the nucleus and the bonding electrons in the outer shell.
Electronegativity decreases down the group as the extra filled main level, increasing the size of the
atom, providing increased shielding, lessens the attraction between the electrons and the nucleus.
MELTING AND BOILING POINTS
Increase down the group. This is because the larger atoms have more electrons; this makes the
V.D.W. forces between the molecules stronger.
The lower the boiling point, the more volatile the element.
TRENDS IN OXIDISING ABLILITY
Halogens usually react by gaining electrons to become negative ions with a charge of -1. So these
reactions are redox reactions.
Cl + 2e 2Cl
The oxidising ability of the halogens decreases as we go down the group.
Halogens will react with metal halides in a solution by displacing a less reactive halogen.
Cl (aq) + 2NaBr (aq) Br (aq) + 2NaCl (aq)
(Sodium ions are spectator ions)
THE OXIDATION OF A HALIDE BY A HALOGEN IS THE BASIS OF A METHOD FOR EXTRACTING
BROMINE FROM SEA WATER.
Cl (aq) + 2Br (aq) Br (aq) + 2CL (aq)
Iodine was discovered by extracting it from kelp which is obtained by burning seaweed. Salts are
removed from the kelp by washing with water. Residue is heated with manganese dioxide and
concentrated SO. 2I + MnO Mn2+ + 2HO + I
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Potassium Chloride Potassium Bromide Potassium Iodide (aq)
Chlorine Water N/A Brown colour Dark brown
Bromine Water No reaction N/A Dark brown
Iodine Solution No reaction No reaction N/A
HALIDE IONS AS REDUCING AGENTS
Halide ions give away/lose es and become halogen molecules.
Increases reducing power down the group as the larger the ion, the more easily it loses an e.
THE REACTIONS OF SODIUM HALIDES WITH SO
SODIUM CHLORIDE (SOLID)
Drops of concentrated sulphuric acid are added to solid sodium chloride.…read more
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IDENTIFYING METAL HALIDES WITH SILVER IONS
Before testing for halide ions you have to remove carbonate and hydroxide impurities as
silver carbonate and silver hydroxide are both insoluble precipitates.
Therefore nitric acid is added first to remove them as you convert them into soluble things.…read more