Group 7 OCR Chemistry AS/A level detailed summary notes/class notes

The halogens
Physical properties:
Þ the halogens are diatomic



Element State Colour Colour of vapour
I 2

Fluorine Gas Pale yellow -

Chlorine Gas Green -

Bromine Liquid Brown Brown

Iodine Solid Grey Purple




Reactivity:
Þ The halogens react by gaining an electron to form 1– Melting
halide ions
Reactivit point
Þ Reactivity decreases down the group because: y
* Atomic radius increases down the group

* The number of electrons increases down
the group

* The number of shells increases down the
Þ This decreases
group the attraction of the nucleus towards electrons due

to electron shielding and the outer shell being further from the nucleus




Melting/Boiling points:
Þ Melting/boiling is caused by intermolecular forces being overcome
by thermal energy

Þ Melting/boiling points increase going down the group because:
* The number of electrons increases down the
group

* Thisthermal
Þ More makes energy
the induced
is dipole-dipole forces
needed to overcome these