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Group 7, The Halogens
The Halogens are Group 7 on the Periodic Table (highlighted in green), as you would expect:
The size of the atoms increase down the group due to the elements gaining an extra
filled main level of electrons.
Atomic (covalent) radius increases down the group due to a greater number of shells.
Melting and boiling points also increase down the group because the atom gets
bigger and Van Der Waals forces get stronger.
Electronegativity decreases down the group due to the increasing atom size.
Halogens usually react by gaining electrons to become negative ions, these reactions are
Redox reactions; halogens are oxidising agents and are themselves reduced.
Cl2 + 2e- 2Cl
The oxidising ability of the halogens increases as we go up the group.
A displacement reaction occurs when Halogens react with metal Halides in solution in such a
way that the Halide in the compound will be displaced by a more reactive halogen (never by a
less reactive one).
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Halide ions can act as reducing agents; in these reactions the halide ions lose (donate)
electrons and become halogen molecules. There is a trend in the reducing ability which is
linked to the size of the ions. The greater the size of the ion, the more easily an electron is
lost due to the electron being further away on an outer shell which is further from the
Increasing reducing power
F- Cl- Br- I-
Ionic Radius 0.133nm 0.180nm 0.195nm 0.…read more