Zusammenfassung der Ressource
Group 7
- Physical properties- Darker
and denser as you go down
- Fluorine = pale yellow gas
- Chlorine = greenish gas
- Bromine = red-brown liquid
- Iodine= black solid
- Size of atoms
- Bigger down the group as
each element has an extra
shell filled.
- Electronegativity
- Decreases down the group
- Because more shells so more
shielding from positive
nucleus so less likely to attract
electron density
- Melting & boiling points
- Increase down a group
- Because the larger the atoms the more
electrons, meaning the van der Waals
forces between molecules are stronger
and require more energy to break
- Chemical reactions
- The oxidising ability of the
halogens decreases down the
group
- Halogens react by gaining electrons to become negative ions.
- They are oxidising agents and they themselves are reduced.
- e.g Cl(2) + 2e- -------> 2Cl-
- Displacement reactions
- Halogens react with metal halides in a
solution so that the halide in the compound
is displaced by a more reactive halogen
- They get less reactive as you go down the group e.g F(2) will displace all other halide
solutions as it is the highest in group 7 where as I(2) will not displace any of the halide
solutions as it is not very reactive
- Halide ions
- Are the group 7 ions. They can act as reducing agents as they
can give away electrons
- The larger the ion the more easily it loses the electron as it
is being held less tightly from the positively charged
nucleus (further away and more electron shielding)
- So...reducing power increases down the group
- All sodium halides react with sulphuric acid.....
- Sodium chloride
- NaCl + H(2)SO(4) ------> NaHSO(4) + HCl
-Steamy fumes of hydrocholoric acid (HX)
- Sodium Bromide
- NaBr + H(2) SO(4) -----> NaHSO(4) + HBr
-Steamy fumes of hydrogen Bromide (HX)
- Redox reactions- Then the Hbr goes under a redox reaction because the sulphur in the suphuric acid is a strong enough oxidising agent to oxidise the bromide.
2H(+) + 2Br(-) + H(2)SO(4) -------> Br(2) + SO(2) + 2H(2)O
- Br(2) produces brown fumes which is bricky colour, so match this with SO(2) as this is acid rain and the acid rain will erode the bricks!
- Sodium Iodide
- NaI + H(2)SO(4) -----> NaHSO(4) + HI
- White stemy fumes of Hydrogen
Iodide (HX)
- Redox reaction- H(2)SO(4) + 8H(+) + 8I(-) -----> H(2)S + H(2)O +4I(2)
- I(2) produces a puple gas
which is like lavender
coloured- so match this
with H(2)S as that's a
smelly egg smell so we
need to cover up that
stench with the lavender.
- Test for iodides
- SN DA CA
- 1. Add SN
- Silver fluoride- no
precipitate
- Silver chloride
-white precipitate
- 2. Add DA
- Disolves
- Silver Bromide-
cream precipitate
- 2. Add DA
- 3. Add CA
- Dissolves
- Silver iodide-
pale yellow
precipitate
- 2. Add DA
- 3. Add CA
- Insoluable
- Silver nitrate... Dilute ammonia...
Concentrated ammonia
- Use of chlorine
- -Poisonous gas
- Soluble in
water