Can you draw Bohr diagrams for flourine and chlorine onto your

worksheet?

Group 7 – the halogensThe elements in group 7 of the periodic table, on the right, are called the halogens.

fluorine

chlorine

bromine

iodine

astatine

I

Br

Cl

F

At

Halogens – what do they look like?

Chlorine Bromine

Iodine

Halogen vapoursBromine and iodine are not gaseous, but have low boiling points. This means that they produce vapour at relatively low temperature. They are volatile.

Bromine produces some red-brown vapour, seen here above the liquid bromine in the jar.

When iodine is heated gently, it changes directly from a solid to a gas without first becoming a liquid.

This is called sublimation.

How does electron structure affect reactivity?The reactivity of halogens decreases going down the group. What is the reason for this?

The atoms of each element get larger going down the group.

This means that the outer shell gets further away from the nucleus and is shielded by more electron shells.

The further the outer shell is from the positive attraction of the nucleus, the harder it is to attract another electron to complete the outer shell.

This is why the reactivity of the halogens decreases going down group 7.

decr

ease

in re

activ

ity

F

Cl

How do halogen molecules exist?All halogen atoms require one more electron to obtain a full outer shell and become stable.

Each atom can achieve this by sharing one electron with another atom to form a single covalent bond.

This means that all halogens exist as diatomic molecules:F2, Cl2, Br2 and I2.

+ F F F F

Halogens in competition

Chlorine is more reactive than iodine or bromine. It can “push” (displace) bromine or iodine out of solution.

Cl2(aq) + 2KBr(aq) 2KCl(aq) + Br2(aq)

Halogens in competition

Chlorine is more reactive than iodine or bromine. It can “push” (displace) bromine or iodine out of solution.

Cl2(aq) + 2KBr(aq) 2KCl(aq) + Br2(aq)

Let’s have a look at some demonstrations of halogens

Starter

• As a group you have 5 min to ‘act out’ a displacement reaction of a halogen and it’s corresponding halide.

• Bonus points for using actual names of the elements/chemicals involved

Halogens in competition

Chlorine is more reactive than iodine or bromine. It can “push” (displace) bromine or iodine out of solution.

Cl2(aq) + 2KBr(aq) 2KCl(aq) + Br2(aq)

Halogens in competition

Chlorine is more reactive than iodine or bromine. It can “push” (displace) bromine or iodine out of solution.

Cl2(aq) + 2KBr(aq) 2KCl(aq) + Br2(aq)

Tasks for this lesson:1. Carry out the practical detailed on your

‘Reactions of the halogens’ sheet (1 per group)

2. On a separate sheet try and write word AND chemical equations for the displacement reactions that DID occur

3. As an extension try and BALANCE the equations

Displacement reactions: summaryThe reactions between solutions of halogens and metal halides (salts) can be summarised in a table:

2KCl + I2

2KBr + I2

halogen

chlorine

bromine

iodine

salt (aq) potassiumchloride

potassiumiodide

potassiumbromide

2KCl + Br2

no reactionno reaction

no reaction

Displacement EquationsPotassium Bromide and Chlorine:• 2KBr + Cl2 2KCl + Br2

Potassium Iodide and Chlorine:• 2KI + Cl2 2KCl + I2

Potassium Iodide and Bromine:• 2KI + Br2 2KBr + I2