Group 7 Elements

The Halogens

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

What are the halogens?

All halogens have seven electrons in their outer shell.

What is the electron structure of the halogens?

fluorine2,7

chlorine2,8,7

bromine2,8,8,7

They can easily obtain a full outer shell by gaining one electron.

They have similar chemical properties.

They all gain an electron in reactions to form negative ions with a -1 charge.

This means that:

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

poisonous and smelly.

brittle and crumbly when solid

What are the general properties of the halogens?

All the halogens are:

They become darker in colour down the group:

non-metals and so do not conduct electricity

is pale yellow

is green-yellow

is blue-black.

is red-brown

What is the physical state of the halogens?

The melting and boiling points of the halogens increase down the group, as the molecules become bigger.

HalogenRelative size Melting point

(°C)Boiling point (°C)

State

-220 -118

-101

-7

114

-34

59

184

gas

gas

liquid

solid

What is the state of each halogen at room temperature?

What are halides?When halogens react with another substance, they become negative ions, as they are gaining an extra electron.

The name of each of the halogens changes slightly once it has reacted – instead of ending with ‘–ine’, they end with ‘-ide’.

Halogen Halidereaction

fluoride (F-)

chloride (Cl-)

bromide (Br-)

iodide (I-)

(F)

(Cl)

(Br)

(I)

When this happens, they are called halides.

Halogens reacting with iron wool

What is the order of reactivity?

How does electron structure affect reactivity?

The reactivity of alkali metals 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

Br

Displacement of halogensIf a halogen is added to a solution of a compound containing a less reactive halogen, it will react with the compound and form a new one.

sodiumchloride

sodiumfluoride

chlorinefluorine + +

F2 (aq) 2NaCl (aq) 2NaF (aq) Cl2 (aq)++

A more reactive halogen will always displace a less reactive halide from its compounds in solution.

This is called displacement.

Displacement of halogensWhy will a halogen always displace a less reactive halogen?

Displacement reactions of halogens

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)potassium

chloridepotassium

iodidepotassiumbromide

2KCl + Br2

no reactionno reaction

no reaction

Is there a displacement reaction?

Halogen Displaceme

nt

Chlorine water

Bromine water

Iodine water KBr added

KI added

KCl added

KI added

KCl added

KBr added

Colour change Yes Yes No Yes No No

Write an equation to show the reactions which are taking place in tubes 1,2 and 4

Reactions of halogens: Summary

What are the uses of halogens?

How many everyday uses of halogens can you see below?What are the uses of halogens?