Physical properties of halogens

Electronic configurations

• Halogens are in group VII of the periodic table and so have seven electrons in their outer shell.

• F 1s2 2s2 2p5• Cl 1s2 2s2 2p5 3s2 3p5• Br 1s2 2s2 2p5 3s2 3p5 4s2 (3d10) 4p5• I 1s2 2s2 2p5 3s2 3p5 4s2 (3d10) 4p5 5s2 (4d10) 5p5

Bonding• Halogens require one electron to

complete their outer shell.

• This can be obtained by gaining an electron to form a halide anion.

• Eg: Cl + e- → Cl-

• Alternatively they can share electrons in a single covalent bond;

•Clx + Hx → ClxxH

Diatomic molecules

• The halogens are found in their native states as diatomic molecules.

• F:F

• Cl:Cl

• Br:Br

• I:I• Halogens form simple molecular lattices held

together by weak van der Waals forces.

Chlorine is a pale green gas at room temp and pressure.

Bromine is an orange brown liquid at room temp and pressure.

It has a low BP and is highly volatile.

Iodine is a grey, silvery solid at room temperature and pressure.

Iodine will not melt, on heating it sublimes, forming a purple gas.

MPs and BPs

MP (oC) BP (oC)

F -220 -188

Cl -101 -35

Br -7 59

I 113

Plot the MPs and BPs and explain the trend in terms of structure/bonding.

MPs and BPs of halogens

• The MPs and BPs increase down the group.

• This is because there are more electrons in the atoms.

• Which means that the van der Waals forces between molecules become stronger.

• So more energy is required to break them and melt or boil the sample.

Solubility of halogens

Organic layer non-polar solvent.

Aqueous layer polar

solvent

Halogens are more soluble in non-polar than in polar

solvents.

The bond between

atoms is not polarised.

Bromine water shaken with hexane.

Chlorine is more soluble in organic

solvents.

Aqueous layer

Chlorine is not very soluble in

water, but reacts to form pale

green chlorine water.

Solubility of chlorine

Solubility of bromine

Bromine readily dissolves in

water to give an orange brown

solution.

Bromine is more soluble in organic

solvents.

Solubility of iodine

Iodine is not very soluble in water.

But it is much more soluble in

KI, giving a yellow brown solution.

Iodine is much more soluble in

organic solvents.

Aqueous layer

Organic layer