The halogens

Question 1

What are group 7 non-metals called?

Answer 1

halogens

Question 2

List the group 7 elements

Answer 2

fluorine
chlorine
bromine
iodine
astatine

Question 3

What type of molecule do the halogens exist as?

Are they toxic or non-toxic?

Answer 3

covalent molecules with 2 atoms

toxic

Question 4

Describe what happens when simple molecular substances melt or boil

Answer 4

• weak intermolecular forces are overcome

- strong covalent bonds joining atoms in molecules don’t break

Question 5

Describe how melting/boiling points change throughout the group and why

Answer 5

melting/boiling points increase down the group

intermolecular forces become stronger further down the group
more heat energy is needed to overcome these forces

Question 6

Describe the approximate range of boiling and melting points in group 7

Answer 6

boiling: ~-120C to ~340C
melting: ~-220C to ~300C

Br (middle):

melting: ~-10C
boiling: ~60C

Question 7

Describe the state at room temperature and colour of group 7 elements

Answer 7

F: very pale yellow gas

Cl: yellow-green gas

Br: red-brown liquid, easily turns to gas

I: shiny grey solid
turns to dark purple gas when heated

At: black solid
purple/blue gas when heated

Question 8

Describe the reactivity of group 7

Answer 8

decreases as you go down the group

F is the most reactive
At is the least reactive

each element can displace the ones below it

Question 9

Explain the change in reactivity as you go down group 7

Answer 9

• 1 electron needs to be gained
• as you go down the group atom size increases
• this increases the distance between the positive nucleus and the negative outer electron
• the forces of attraction weaken
• this makes it more difficult to gain(/attract) an electron in the outer shell

Question 10

Chlorine is manufactured on an industrial scale by the electrolysis of concentrated sodium chloride solution

Describe a simple laboratory test for the presence of chlorine

Answer 10

• place a piece of damp litmus paper into the container

- if chlorine is present the litmus paper turns red, then is bleached white

Question 11

Astatine is a rare, radioactive element placed immediately below iodine in group 7.

a) suggest why astatine is thought to be dark in colour, even though no one has seen it
b) predict the melting point of astatine, and justify your answer

Answer 11

a) the other, known elements get darker going down the group, it is believed that astatine follows the same pattern

b) (250C to 350C)
melting points increase moving down the group by around 100C to 200C each time