Halogens

Question 1

The Halogens

Answer 1

The elements in Group 7 are called the halogens

The halogens include flourine, chlorine, bromine, iodine and astatine

They all have 7 electrons in their outer shell and so they react in a similar way.

Question 2

Elements and their colour + physical state at room temperature

Answer 2

Flourine - yellow - gas

Chlorine - green - gas

Bromine - red brown liquid/ orange brown vapour - liquid

Iodine - grey solid, purple vapour - solid

Question 3

Properties

Answer 3

The melting and boiling points tend to increase down the group.

The halogens have poisonous vapours and have to be handled in a fume hood.

Liquid bromine is also very corrosive and has to be used carefully and you have to make sure it doesn’t go on your skin.

Question 4

Reactions of halogens

Answer 4

The halogens react with hydrogen to form hydrogen halides. For example, when flourine reacts with hydrogen, it forms hydrogen flouride.

Or when chlorine reacts with hydrogen, it forms hydrogen chloride

Or when bromine reacts with hydrogen, it forms hydrogen bromide

And finally when iodine reacts with hydrogen it forms hydrogen iodide.

The hydrogen halides (hydrogen chloride, hydrogen bromide etc) are all acidic and poisonous gases.

Question 5

Displacement Reactions

Answer 5

Reactivity decreases down Geoup 7. This means that flourine is the most reactive halogen.

The reason for this is that the number of shells that are occupied increase because the periods are different for each element. So the electron being gained is further away from the nucleus so it is less attracted to it and so it is harder to gain an electron.

A more reactive halogen will displace a less reactive halogen from a solution of one of its compounds. The least reactive halogen doesn’t displace the most reactive halogen from its compound.

For example:

Potassium iodide + chlorine —> potassium chloride + iodine

Chlorine is more reactive than iodine and so has separated the iodine from its compound and replaced it with itself.

However, if the compound’s halogen is the highest reactivity it can be, there will be no reaction

For example:

Potassium chloride + bromine

There will be no reaction because chlorine is already there and is the most reactive out of the two.

Question 6

Astatine

Answer 6

Because astatine is radioactive and rare, we can’t find it. So all we can do is make predictions using the Periodic Table:

1. We know as we go down the group, it becomes less reactive, therefore we know that astatine is less reactive than iodine.
2. We know that the melting and boiling points increase down the group, therefore astatine has a higher melting and boiling point than iodine.
3. We know that as you go down the group, the colour becomes darker, therefore astatine will have a darker colour than iodine.