6.2 Group 7

Question 1

Colours of pure halogens

Answer 1

Fluorine - yellow
Chlorine - green
Bromine - brown
Iodine - grey / black
Astatine - black

Question 2

Colour of dissolved halogens

Answer 2

Fluorine - colourless
Chlorine - colourless, possibly pale green
Bromine - orangey / yellow
Iodine - brown
Astatine - doesn’t dissolve

Question 3

Melting and boiling point of halogens

Answer 3

There are strong covalent bonds between the atoms but there are weak intermolecular forces between molecules. The intermolecular forces are weaker in smaller molecules and as the size of the atom increases as you go down group 7 the melting and boiling point does too.

Question 4

Test for chlorine

Answer 4

Damp blue litmus paper is used and if chlorine is present it will turn red and then become bleached (turn white).
Cl + H2O —- HCl + HOCl
the hydrochloric acid turns the litmus paper from blue to red and the hypochlorous acid bleaches it.

Question 5

Metal halides

Answer 5

The halogens react with some metals to form ionic compounds which are metal halide salts.
The rate of reaction is slower for halogens which are further down the group such as bromine and iodine.

Question 6

Hydrogen halides

Answer 6

The halogens react with nonmetals to form simple molecular covalent structures.
Hydrogen halides are steamy acidic gases that dissolve very well in water to form strongly acidic solutions.

Question 7

Displacement reaction

Answer 7

A halogen displacement reaction occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide.
If the halogen element is less reactive then there will be no reaction.

Question 8

Halogen displacement and redox

Answer 8

Oxidation is loss of electrons and reduction is the gain of electrons.
Halogen displacement reactions are redox reactions.

Question 9

Reactivity of halogens

Answer 9

Halogen atoms gain electrons to obtain a full outer shell like a noble gas. the nearer the outer shell is to the nucleus, the stronger the attraction for the incoming electron and so the more reactive the halogen is. as you go down group 7 the size of the atoms becomes larger and the further the nucleus is from the outer shell. this means that the attraction for the incoming electron and the nucleus becomes weaker and the halogens get less reactive towards the bottom of the group.