ES - Group 7 The halogens

Question 1

What are halogens?

Answer 1

The highly reactive non-metals of group 7.

Question 2

What happens to the volatility of the elements as you go down group 7?

Answer 2

Become less volatile.

Question 3

What is volatility?

Answer 3

A measure of how easy it is to vaporise something (turn it into a gas).

Question 4

Why does the volatility of the group 7 elements decrease as you go down the group?

Answer 4

Because of the increasing strength of the instantaneous dipole-induced dipole bonds - these increase as the size and relative mass of the atoms increase.

Question 5

What can you use to see the trend in volatility of the group 7 elements?

Answer 5

Their appearance at RTP.

Question 6

What is the appearance of fluorine at RTP?

Answer 6

Pale yellow gas.

Question 7

What is the appearance of chlorine at RTP?

Answer 7

Yellow-green gas.

Question 8

What is the appearance of bromine at RTP?

Answer 8

Red-brown liquid.

Question 9

What is the appearance of iodine at RTP?

Answer 9

Shiny grey solid.

Question 10

Compare the solubility of the halogens in organic solvents and in water:

Answer 10

More soluble in organic solvents than in water.

Question 11

What do halogens exist as in their natural state?

Answer 11

Covalent diatomic molecules.

Question 12

Why do the halogens have a low solubility in water?

Answer 12

Because they’re covalent and non-polar.

Question 13

What is the solubility of halogens like in water?

Answer 13

Low.

Question 14

What is the solubility of halogens like in organic solvents?

Answer 14

High - dissolve easily.

Question 15

What is the colour of chlorine in water?

Answer 15

Virtually colourless.

Question 16

What is the colour of bromine in water?

Answer 16

Yellow/orange.

Question 17

What is the colour of iodine in water?

Answer 17

Brown.

Question 18

What is the colour of chlorine in hexane?

Answer 18

Virtually colourless.

Question 19

What is the colour of bromine in hexane?

Answer 19

Orange/red.

Question 20

What is the colour of iodine in hexane?

Answer 20

Pink/violet.

Question 21

How does the reactivity of the halogens change down the group?

Answer 21

They get less reactive as you go down the group.

Question 22

How do halogen atoms react?

Answer 22

By gaining an electron in their outer p sub-shell.

Question 23

In reaction, are halogens oxidised or reduced?

Answer 23

Reduced - they gain electrons.

Question 24

Are halogens oxidising or reducing agents?

Answer 24

Oxidising - as they are reduced, they oxidise another substance (it’s a redox reaction).

Question 25

Why do the halogens get less reactive down the group?

Answer 25

The atoms become larger, so their outer electrons are further from the nucleus. The outer electrons are also shielded more from the attraction of the positive nucleus, because there are more inner electrons. This makes it harder for larger atoms to attract the electron needed to form an ion - so larger atoms are less reactive.

Question 26

What can halogens do to halide ions from solution?

Answer 26

Displace them.

Question 27

What is a displacement reaction?

Answer 27

A type of reaction where one reactant replaces another reactant in a compound.

Question 28

What will displace what in a displacement reaction?

Answer 28

A more reactive halogen will displace a less reactive halide in a solution.

Question 29

What will chlorine displace?

Answer 29

Bromide and iodide ions.

Question 30

What will bromine displace?

Answer 30

Iodide but not chloride ions.

Question 31

What will iodine displace?

Answer 31

Not chloride or bromide ions.

Question 32

What type of reaction is a displacement reaction between halogens and halides?

Answer 32

A redox reaction.

Question 33

The thing that is displaced is...

Answer 33

...oxidised.

Question 34

The thing that does the displacing is...

Answer 34

...reduced.

Question 35

What change in appearance would there be if a reaction takes place between a halogen and halide?

Answer 35

A colour change.

Question 36

If bromide is displaced and bromine is formed, what colour would the reaction mixture turn?

Answer 36

Orange.

Question 37

If iodide is displaced and iodine is formed, what colour would the reaction mixture turn?

Answer 37

Brown.

Question 38

How can you make the colour change due to a displacement reaction easier to see?

Answer 38

Shake the reaction mixture with an organic solvent like hexane as the halogen that is present will dissolve in the organic solvent which settles out as a distinct layer above the aqueous solution.