group 7 Flashcards
what is fluorine like at room temp
pale yellow gas
what is chlorine like at room temp
pale green gas
what is bromine like at room temp
brown orange liquid
what is iodine like at room temp
grey solid
bpt trend
increases as we go down group because van der waals forces increase due to increase in size and mass of atoms
electronegativity trend
decreases down the group as the atoms get larger and the distance between positive nucleus and bonding electrons increases and there is more shielding
reactivity trend
decreases as we go down the group as for a reaction to occur gain electron and smaller atom radius attract electrons better than large atoms
halogen are less … as we go down the group
oxidising
how is bleach made
via a disproportionation reaction
mixing chlorine and sodium hydroxide will form sodium chlorate (|)
why is it called a disproportionation reaction
chlorine has been simultaneously reduced and oxidised
uses of sodium chlorate
treating water
bleaching paper and fabrics
cleaning agents
adding chlorine to water can …
kill bacteria
what happened when chlorine is added to water
produces chlorate ions which kill bacteria and is useful in drinking water and pools
this is a disproportionation reaction
… can decompose chlorinated water
sunlight and it can means no ClO- is made so cannot kill bacteria
what are advantages of chlorinating drinking water
destroys microorganisms that cause disease
long lasting so reduces bacteria build up further down the supply
reduces growth of algae that discolours water and can give bad taste
what are disadvantages of chlorinating drinking water
chlorine gas is toxic and irritate respiratory system
liquid chlorine causes chemical burns to the skin
chlorine can react with organic compound present to make chloroalkanes which have been linked to causing cancer but risk of not chlorinating could lead to cholera epidemic
halide ions lose electrons so the are … agents
reducing
reducing power trend
down the group ionic radius increases
the distance between nucleus and outer electrons becomes larger and more shielding. attractive force gets weaker
outer electron is lost more readily so lower down group better at reducing
tests to prove trend of reducing power
reaction w sulphuric acid- some halide ions can reduce conc sulfuric acid
reaction of halides with sulfuric acids
A-makes white misty fumes, produces NaHSO4
B- redox half equations- Br oxidised, S reduced, produces SO2- orange vapour of Br2
C- I- oxidised, sulfur being reduced, produces S- yellow solid of S produced
D- I- ions oxidised, S being reduced produces H2S - rotten egg smell of H2S produced
Cl- A
Br- A+B
I- A+B+C+D
reaction of halides with silver nitrate
add dilute nitric acid- to react with any other anions to prevent false results
then silver nitrate solution
Cl- white precipitate
I- yellow precipitate
Br- cream precipitate
further test of ammonia
Cl- dissolves in dilute NH3
Br- dissolves in concentrated NH3
I- insoluble in concentrated NH3
