group 7 Flashcards
trend electronegativity
decreases
larger atoms so larger atomic radius so increased distance between nucleus and shared pair
increased shielding means e- density in cov bond is further from nucleus
decreased FoA, decreased ability
boiling pints
increases
larger molecules so vdw forces between molecules are stronger
more energy to overcome
trend atomic radius
increases
atoms are larger so there are more e- and the gore more completed energy levels
trend in 1st ionisation energy
decreases
bigger atoms
larger radius
increase shielding
more shells
weaker FoA between.. .
e is more easily lost
increased nuclear charge overcome by these effects
halogen molecules profiles - state, characteristics, colour
fluorine
F2
gas at room temp
yellow
toxic
v reactive
halogen molecules profiles
chlorine
Cl2
toxic
v reactive
gas at room temp
green
halogen molecules profiles
bromine
Br2
toxic
reactive
liquid at rtp
orange
halogen molecules profiles - state, uses, colour
iodine
I2
solid r rto
grey silver black
sublimes straight to gas, purple - why?
Van der Waals forces that link iodine molecules together in a crystal are relatively weak. That is why iodine usually sublimes very easily (that is, passes directly from the solid to the gaseous state) without going through the liquid state.
uses: tests for starch
stains cells
antiseptic solution
reaction of chlorine with water (no sunlight)
importance of product
Cl2 + H2O (reversible) HCl + HClO
HClO is chlorate acid which dissociated to produce H+ and ClO- ions
ClO- is a powerful oxidising agent which kills bacteria BC if oxidises things in bacteria
uses as
- water treatment
- food disinfectant
- wound treatment
—
products also written as 2H+ + Cl- + ClO-
reaction of chloride and water (sunlight)
Cl2 + H2O – 4Hcl + O2
not good bc no HClO
so need to replenish regularly in pools
reaction of chlorine and sodium hydroxide
conditions
uses
Cl2 + NaOH – NaCl + NaClO + H2O
conditions: cold, dilute, aq NaOH
NaClO = sodium chlorate - bleach therefore uses as
- cleaning agent
- disinfectant
- cleaning agent
- waste water treatment
what is the trend in oxidising ability of the halogens
explain
decreases
oxidising agent undergoes reduction so it gains e-.
because as go down there are more completed energy levels resulting in increased shielding and atomic radius,
eFoA is weaker between nucleus and e to gain so it’s harder to gain
outline a test you can use to prove the oxidising ability of halogens
- In a spotting tile put Cl2, BR2, and I2 in each row
- put H2O in one column (control)
- KCl in one column
- KBr in one column
- KI in one column
- the more powerful oxidising agent will displace the other halide in the metal halide
- Cl2 displaces Br and I
- in Cl2 with KBr or KI, goes from colourless to orange// brown showing Br2//I2 formed - Br2 displaces I not Cl
- in BR2 with KCl there is no change, remains colourless
- with KI goes from colourless to brown showing I2 formed - I2 doesn’t replace Br and Cl, remains brown (?)
ionic equations for oxidising ability of halogens
Cl2 + 2Br- – 2Cl- + Br2
etc etc (symbols all aq)
trend and explanation of reducing power of halide ions
increases as go down
outer e- being lost (is a 1- ion so has an extra electron. losing it makes them atoms) is further from nucleus due to ions getting bigger so more completed energy levels. increased shielding. so weaker eFoA so e- is more easily lost
reducing power = reducing agent, gets oxidised so losing e-
how can we evidence reducing power
reaction of solid sodium halide with conced sulfuric acid (so symbol l)
1/2 spatula solid
5 drops acid
what’s the general equation for the reaction of solid sodium halide with sulfuric acid
observation
which to halide salts don’t have further reactions
NaX (s) + H2SO4 (l) – HX (g) + NaHSO4 (s)
white misty fumes of hydrogen halide gas
chlorine (the gas is hydrogen chloride not hydrochloric acid) and fluorine don’t do anything more than this. they are not strong enough reducing agents
(R1: NaX + H2SO4 – HX + NaHSO4)
general equation for HX gas formed in reaction 1, with H2SO4
which halides undergo this 2nd reaction
HX (g) + H2SO4 (l) – X2 (g) + SO2 (g) + 2H2O (l)
produces halogen molecule, sulfur dioxide and water
HBr and HI (bromide, iodide)
(R1: NaX + H2SO4 – HX + NaHSO4)
(R2: HX (g) + H2SO4 (l) – X2 (g) + SO2 (g) + 2H2O (l))
—-
—-
observations with Br
1: white misty fumes of HBr gas
2:
- brown fumes from BR2 gas (reaction is exothermic so liquid Br vaporises)
- choking fumes from SO2 which is colourless
(R1: NaX + H2SO4 – HX + NaHSO4)
(R2: HX (g) + H2SO4 (l) – X2 (g) + SO2 (g) + 2H2O (l))
—-
—-
observations with I
1: white misty fumes
2: v exothermic so solid iodine vaporises to purple fumes of I2 vapour ;
choking fumes from SO2
(R1: NaX + H2SO4 – HX + NaHSO4)
(R2: HX (g) + H2SO4 (l) – X2 (g) + SO2 (g) + 2H2O (l))
there is a third equation involving the HX and the SO2 formed in R2.
which halogen undergoes this one
what’s the eq for it
observations
iodine
6HI + SO2 – H2S + 3I2 + 2H2O (g/g/l)
- purple fumes of iodine vapour (will have alr been there from 2nd reaction, so more thick ig)
- rotten egg smell from hydrogen sulfide
- yellow solid observation due to sulfur
6HI + SO2 – H2S + 3I2 + 2H2O (g/g/l)
there is a yellow solid observation due to sulfur. explain
ox state in SO2 = +4
ditto H2S = -2
therefore had to pass 0
so was an element for a sec
sulfur solid is yellow
equations for investigating reducing power of halogens is as shown
R1: NaX + H2SO4 – HX + NaHSO4
R2: HX (g) + H2SO4 (l) – X2 (g) + SO2 (g) + 2H2O (l)
3: 6HI + SO2 – H2S + 3I2 + 2H2O (g/g/l)
who is redox and who is not
1 not - this is an acid base reaction
2 3 are - these are redox reactions where HX is the reducing agent (gets oxidised, losing e-) and sulfuric acid acts as the oxidising agent (gains e-)
which of the reactions of solid sodium halide and sulfuric acid conced,
have the observation of purple fumes
ionic equations for this
R2/3 with NaI
2I- + H2SO4 + 2H+ —- I2 + SO2 + 2H2O
which of the reactions of solid sodium halide and sulfuric acid conced,
have the observation of choking fumes
ionic equations for this
R2 and final of NaBr
R2[/3(reactant)] of NaI
2I- + H2SO4 + 2H+ —- I2 + SO2 + 2H2O
which of the reactions of solid sodium halide and sulfuric acid conced,
have the observation of rotten egg smell
ionic equations for this
r3 of NaI
actually the HI with the SO2
8I- + H2SO4 + 8H+ —- 4I2 + H2S + 4H2O
which of the reactions of solid sodium halide and sulfuric acid conced,
have the observation of yellow solid
ionic equations for this
3rd reaction NaI
actually HI with SO2
6I- + H2SO4 + 6H+ —– 3I2 + S + 4H2O
how to test for halide ions in solution
- acidify 2cm3 sample with 5 drops HNO3 j not HCl
this removes impurities because ions present will bond to these ions
1.5 add water / make into a solution
- add 5 drops AgNO3 solution
- if halide ions present a silver halide precipitate forms
- AgCl is white
- AgBr is cream
- AgI is yellow
by using acidified silver nitrate you can distinguish halide ions in solution
how do you distinguish the silver halides formed
- add 1cm3 dilute ammonia to each ppt
- silver chloride redissolves
AgCl (s) + 2NH3 (aq) —- (Ag(NH3)2)+ (aq) + Cl- (aq) - there is no visible change for the others. ppt remains
- add 1cm3 conced ammonia (need gloves)
- AgBr redissolves
AgBr (s) + 2NH3 (aq) —- (Ag(NH3)2)+ (aq) + Br- (aq) - AgI doesn’t redissolve
why is fluorine not including in the acidified silver nitrate test
AgF is soluble, doesn’t give ppt
there is a large difference in the atomic size of the silver and the atomic size of fluoride, as a result, the bond formed between the silver and fluorine atom will not be very strong and can be easily broken by hydration energy, so it has a high solubility in water.
why is fluorine not involved in the oxidising power experiment (F2 with KCl, KBr, KI)
it reacts fully with water
with less amount of F2 fed slowly into water:
F2 + H2O — HF + O2
with excess fed quickly:
F2 + H2O — HF + O3
disproportionation
when in a reaction an element is simultaneously oxidised and reduced.
in the reaction of chlorine with water (no sunlight) or NaOH, chlorine goes from ox state 0 — ox state of +1 in HClO / NaClO ,, and ox state of in -1 HCl
colour of halogen water
Cl2 Aq. Pale green
Br2 Aq. Orange brown
I2 aq. Dark brown
