3.2.5 Group 7(17), the Halogens - Trends in physical properties

Specification

The elements of group 7 (Fluorine to Iodine)

Atomic radius increases in size from F to I because the number of electron shells increases from F to I

Ionic radius increases from F to I because the number of electron shells increases from F to I

Electronegativity

Electronegativity decreases because the attracting power of the nucleus is shielded by the inner electron shells increasingly as the group is descended.

Ionisation energy decreases descending the group because the shielding effect (repulsion caused by the inner electrons) of the inner electron shells increases as you go down the group and so the outer electron is more easily removed

Melting point

The melting point increases from F to I, because the larger halogens have greater Van der Waals' forces (London dispersion forces) holding the molecules together, as the relative mass increases descending the group

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