3.1.10 Group 17: the Halogens

Question 1

In an organic solution, which colour does Iodine turn?

Answer 1

Purple;

Question 2

In an aqueous solution, which colour does Iodine turn?

Answer 2

Brown;

Question 3

Formula for iodine;

Which colour and state is this alone and why?

Answer 3

1. I2: diatomic;
2. A grey solid;
3. This is because iodine is the furthest down the group, with the most protons and electrons. Therefore, despite its greater effective nuclear charge, it has so many London dipole-induced dipoles, that these IM bonds (physical not chemical) keep it solid;

Question 4

What is the test for the iodine halide ion?

Answer 4

Test for the I- halide ion by:
1. Add dilute nitric acid to remove ions that might interfere with the test;
Ag+(aq) +X-(aq halide ion) = Agx(s)
2. The AgX(s) is a solid precipitate
If this is yellow and insoluble in ammonia, this is iodine;

Question 5

What is a halide ion?

Answer 5

A halide ion is a - ion that the group 7 halogens make when they are reduced - therefore, they are oxidising agents;
The halogens do this in order to gain a noble gas configuration;

Question 6

How does reactivity change down group 7?

Answer 6

1. Reactivity decreases down the halide group;
2. G7 elements react in order to be oxidised;
3. In order to do this, they must gain an electron;
4. The higher up the group, the electrons are closer to the positive nucleus;
5. This means that there is less distance and shielding from the nucleus;
6. Even though there is less effective nuclear charge higher up the group (as there are less protons in the nucleus), effective nuclear attraction is greater, as there is a lack of shielding - and so electrons are more easily gained.
7. This means that the higher up the group, the more reactive an element.
8. Therefore iodine is the least reactive halogen, and so its halides will be displaced by every other element in the group;

Question 7

What does the electronic configuration of Iodine end in?

Answer 7

5p5;

Question 8

In an organic solution, which colour does Bromine turn?

Answer 8

Orange;

Question 9

In an aqueous solution, which colour does Bromine turn?

Answer 9

Yellow, as bromine water is yellow;

Question 10

Formula for Bromine ;

Which colour and state is this alone and why?

Answer 10

Br2: diatomic;

2. A red-brown liquid;
3. This is because bromine is in the middle of the group with enough protons and electrons to create some London forces, which stop it being completely in the gaseous state. These London forces are not sufficient enough, however to make it so that the element is a solid state.

Question 11

What is the test for the Bromine halide ion?

Answer 11

Test for the Br- halide ion by:
1. Add dilute nitric acid to remove ions that might interfere with the test;
Ag+(aq) +X-(aq halide ion) = Agx(s)
2. The AgX(s) is a solid precipitate
If this is cream and soluble in ammonia, this is bromine;

Question 12

What does the electronic configuration of Bromine end in?

Answer 12

4p5;

Question 13

In an organic solution, which colour does chlorine turn?

Answer 13

colourless;

Question 14

In an aqueous solution, which colour does chlorine turn?

Answer 14

Colourless: because chlorine water is colourless;

Question 15

Formula for chlorine;

Which colour and state is this alone and why?

Answer 15

Cl2: diatomic;

2. A green gas;
3. This is because chlorine is towards the top of the group with not enough protons and electrons to create any London forces, which cause it to be completely in the gaseous state.

Question 16

What is the test for the chlorine halide ion?

Answer 16

Test for the Cl- halide ion by:
1. Add dilute nitric acid to remove ions that might interfere with the test;
Ag+(aq) +X-(aq halide ion) = Agx(s)
2. The AgX(s) is a solid precipitate
If this is white and soluble in ammonia, this is iodine;

Question 17

What does the electronic configuration of chlorine end in?

Answer 17

3p5;

Question 18

What do all of the group 7 halogens end in (electron configuration wise)?

Answer 18

a p orbital, which has five electrons;

Question 19

Why does chlorine displace most of the elements in the halogen group 7, and which element does it not displace?

Answer 19

It does not displace fluorine, because this is more reactive than chlorine. However, it displaces every other element in the group because it is more reactive than them.

Question 20

Formula for fluorine;

Which colour and state is this alone and why?

Answer 20

1. F2: diatomic;
2. A pale yellow gas;
3. This is because fluorine is at the top of the group with not enough protons and electrons to create any London forces, which cause it to be completely in the gaseous state.

Question 21

What does the electronic configuration of fluorine end in?

Answer 21

2p5 (as there is no such thing as the 1p orbital, it must start with fluorine ending in the 2p orbital, with five electrons, like any group 7 halogen element)

Question 22

Name any displacement reactions that chlorine has with other group 7 halide ions.

Answer 22

1. Displaces Br-:
   Cl2(aq)+2Br-(aq)=2Cl-(aq) +Br2(aq)
2. Displaces I-:
   Cl2(aq)+2I-(aq)=2Cl-(aq) +I2(aq)

Question 23

Name any displacement reactions that bromine has with other group 7 halide ions.

Answer 23

Displaces I-:

Br2(aq)+2I-(aq)=2Br-(aq) +I2(aq)

Question 24

Name any displacement reactions that iodine has with other group 7 halide ions.

Answer 24

1. No reaction with F-, Cl- or Br-;

2. As is the least reactive element in the group;

Question 25

Why does fluorine not appear in displacement reactions?

Answer 25

It is so reactive that the displacement reactions would be dangerous. The diatomic element would displace any of the halide elements of the halogen group 7.