Group 7 Flashcards
How do group 7 elements exist?
As diatomic molecules
How many electrons do group 7 elements have in their p orbitals?
nP5
Trend in boiling point down the group
Increases
- increased London forces due to more electrons
- more energy required to separate the molecules
Physical state of Chlorine at room temperature
Gas (green)
Physical state of Bromine at room temperature
Liquid (red-brown)
Physical state of Iodine at room temperature
Solid (grey/black)
Trend in electronegativity going down the group
Decreases down the group
- increased distance from nucleus
- more shielding
These two factors cancel out the effect of increased nuclear charge
Trend in atomic radius going down group 7
Increases
Trend in ionic size going down the group
How does this compare with the size of the atoms of the elements?
Increases
Ions are larger due to increased number of electrons
This means the force of attraction from the nucleus is spread more thinly so electrons move further out
Trend in oxidising ability going down the group
Explain the trend
Decreases
- less attraction from the nucleus due to increased distance
- more shielding
Which halogen out of Cl, Br and I is best at displacing other halogens?
Give the order of displacement
Cl
Cl > Br > I
Give the equation for the oxidation of bromide ions using chlorine
Cl2 + 2Br- –> Br2 + 2Cl-
Give the equation of bromine oxidising Iodide ions to iodine
Br2 + 2I- –> I2 + 2Br-
Give the equation for the reaction of chlorine with sodium bromide
Cl2 + 2NaBr –> 2NaCl + Br2
Give the equation for the reaction of chlorine with water and the results of testing the reaction with litmus paper
Cl2(g) + H20(l) ⇌ HCl(aq) + HOCl(aq)
Litmus would turn red, due to the HCl, and then be bleached white by the HOCl
Give a use of NaClO
Active ingredient in household bleach
Equation for the reaction of chlorine with cool, dilute aqueous sodium hydroxide
What type of reaction is it?
Cl2 + 2NaOH –> NaCl + NaClO +H2O
Disproportionation as the chlorine is both oxidised and reduced
Give another name for sodium chlorate(I)
Sodium hypochlorite
Give the equation of the reaction between chlorine with hot, concentrated sodium hydroxide solution
3Cl2 + 6NaOH –> 5NaCl + NaClO3 + 3H2O
What is the name of NaClO3?
Sodium chlorate(V)
Which halide ion is the most reducing?
Why?
I-
-as ionic radius increases, it becomes easier to remove outer electrons
Describe the test for halides using silver nitrate
- Add dilute nitric acid to the sample containing the halide
- Add a few drops of silver nitrate solution
- Observe colour of precipitate of silver halide
Describe what you would do to precipitates formed from adding silver nitrate to solutions containing halides. Give the results
- Add dilute ammonia solution
- If precipitate still exists, add concentrated ammonia solution
Silver chloride - dissolves in both dilute and concentrated ammonia solution
Silver bromide - dissolves in concentrated ammonia solution but not in dilute
Silver Iodide - doesn’t dissolve in either
Give the colours of the precipitates formed from the three halides reacting with silver nitrate solution
Chloride - White ppt
Bromide - Cream ppt
Iodide - Yellow ppt
What is the complex formed when a silver halide is dissolved in ammonia?
[Ag(NH3)2]+
Colourless diammine complex
Write the equation for the partial ionisation of sulfuric acid
H2SO4 ⇌ H+ + SO4 2-
Three possible reduction products of sulfuric acid
Sulfur dioxide - SO2
Sulfur - S
Hydrogen sulfide - H2S
What happens when you add concentrated sulfuric acid to the halides?
- Sulfuric acid displaces the weaker acids HCl, HBr and HI from their salts
- Hydrogen halides all fume in moist air
- Sulfuric acid is reduced to lower oxidation states of Sulfur the further you go down the group
What are the products when concentrated sulfuric acid is added to a solution of NaCl?
Give the equation and any observations
HCl produced
White, misty fumes given off
NaHSO4 also produced
NaCl + H2SO4 –> NaHSO4 + HCl
Give the products, equations and observations for when concentrated sulfuric acid is added to NaBr
NaBr + H2SO4 –> NaHSO4 + HBr
The HBr then goes on to react with the sulfuric acid:
2HBr + H2SO4 –> 2H2O + SO2 + Br2
HBr - misty fumes
Br2 - brown fumes
SO2 - Colourless gas with a choking smell
What are the two half equations for the reaction of NaBr and H2SO4?
2Br- –> Br2 + 2e-
H2SO4 + 2H+ + 2e- –> 2H2O + SO2
Give the products, equations and observations for the reaction of NaI and H2SO4
NaI + H2SO4 –> NaHSO4 + HI
Hydrogen iodide goes on to react with H2SO4:
6HI + H2SO4 –> 4H2O + S + 3I2
Sulfuric acid is reduced to hydrogen sulfide:
H2SO4 + 8e- + 8H+ –> H2S + 4H2O
Observations:
HI - misty fumes
I2 - purple fumes or black solid
SO2 - colourless gas with choking smell
S - yellow solid
H2S - colourless gas with rotten egg smell
What is the trend in temperature of the hydrogen halides?
HF > HCl > HBr > HI
How does reducing ability of the hydrogen halides change as you go down the group?
Increases
-due to bond strength decreasing
Uses of chlorine
- Water purifier
- bleach
- solvents
- CFC’s
Equation of HBr reacting with water
HBr + H2O –> H3O+ + Br-
Forms hydrobromic acid and bromide ions
Give the equation for the reaction between hydrogen chloride and water
HCl + H20 –> H3O+ + Cl-
Forms hydrochloric acid
Give the equation for the reaction between HI and H2O
HI + H20 –> H3O+ + I-
Products of hydrogen halides reacting with ammonia.
Give an example
Form salts which are white ionic solids
Give the equation for the reaction between hydrogen chloride gas and ammonia gas
NH3(g) + HCl(g) –> NH4Cl(s)
What is special about fluoride ions when you add silver nitrate to them?
They don’t form a silver halide precipitate
