4.3 HALOGENS Flashcards
how are the elements bonded?
- covalently bonded
- simple molecular substances
properties of group 7 elements:
- all diatomic
- colours get darker down the group
- melting/ boiling point increases down the group
colour of fluorine:
- F2
- very pale yellow
- gas
colour of chlorine:
- Cl2
- pale green
- gas
colour of bromine:
- Br2
- brown
- liquid
- volatile
- releases brown fumes
colour of iodine:
- I2
- dark grey
- solid
- sublimes
- releases purple fumes
colour of astatine:
- At2
- black
- solid
what do halogens form when they react with metals?
ionic compounds
what happens to reactivity as you go down the group?
get less reactive
why do the halogens get less reactive as you move further down the series?
- all halogen atoms need to gain an electron to fill their outer shell
- this happens less easily as you go down the group because:
- atoms have more electron shells
- the extra electron is further from the nucleus
- so its attraction to the nucleus is weaker
test for chlorine:
damp blue litmus paper turns white because chlorine acts as a bleaching agent
what do hydrogen and chlorine react to form?
hydrogen chloride (colourless)
why does the reaction of hydrogen and chlorine produce a colour change?
- due to the substances involved
- HCl is a covalently bonded, simple molecular substance
- it is a gas because it has a low boiling point due to weak IMFs
what happens when you dissolve HCl into water?
- HCl (g) dissolves to form HCl (aq)
- HCl (aq) dissociates to form H+ (aq)
- the H+ (aq) is acidic
- HCl (aq) is called hydrochloric acid
what happens when you dissolve HCl into methylbenzene?
- HCl (g) dissolves to form HCl (org)
- HCl (org) cannot dissociate
- there is no H+ (org)
- HCl (org) is not acidic
what is a displacement reaction?
more reactive halogens can displace less reactive halogens from their compounds
what colours are aqueous halogens Cl2, Br2 and I2?
- Cl2- colourless
- Br2- yellow
- I2- brown
what colours are the aqueous salts KCl, KBr, Kl?
all colourless
what happens when you react KBr and Cl2?
Cl2 + 2KBr—> Br2 + 2KCl
- chlorine displaces bromine
- colourless —–> yellow
what happens when you react KI and Cl2?
Cl2 + 2Kl—> I2 + 2KCl
- chlorine displaces iodine
- colourless—-> brown
what happens when you react KCl and Br2?
- no change
- stays yellow
what happens when you react KI and Br2?
Br2 + 2Kl—> I2 + 2KBr
- bromine displaces iodine
- yellow—-> brown
what happens when you react KCl and I2?
- no change
- stays brown
what happens when you react KBr and l2?
- no change
- stays brown
what do the displacement reactions infer:
the reactivity trend is chlorine> bromine> iodine
all halogen displacement reactions are…
redox reactions
