Group 7 Flashcards
What are all the group 7 element appearance and state at room temperature?
Fluorine - pale yellow gas
Chlorine - pale green gas
Bromine - dark red liquid
Iodine - grey solid but sublimes into a purple vapour when slightly heated
Astatine - black solid
What is the trend in atomic radius going down group 7 and why?
Atomic radius increases down group 7 because of the additional electrons in each shell
What is the trend in melting and boiling point going down group 7 and why?
Melting and boiling point increases down group 7 because the atoms get bigger down the group which means more van der waals forces and the strength of the van der waals forces increase down group 7 which requires more energy to overcome.
What is the trend in electronegativity going down group 7 and why?
Electronegativity decreases down group 7 because the size of the atom gets bigger due to increased shielding and atomic radius which means weaker attraction between nucleus and outer electrons
What is the trend in bond enthalpy going down group 7 and which element is an exception and why?
Bond enthalpy decreases down group 7 because shielding increases which outweighs the increase in nuclear charge.
Fluorine atoms are small and are so close together that the lone pairs of electrons around each atom repel each other so the bond is weakened which results in a very low bond enthalpy.
What is the trend in reactivity down group 7?
Reactivity decreases down group 7 because atomic radius and shielding increases which makes it harder to gain an electron because of the weaker electrostatic force between the positive nuclei and negative electron.
What is the trend in the 1st ionisation energy down group 7?
The ionisation energy decreases down group 7 because shielding increases down group 7 which makes it easier to lose the outer electron.
What are oxidising agents?
Electron acceptors that are being reduced themselves.
What is the trend in oxidising power down group 7?
Oxidising power decreases down group 7 because shielding and atomic radius increase down group 7 which makes it harder to attract an electron due to the weaker electrostatic force.
How is bleach made?
Via a disproportionation reaction
- Mixing chlorine and sodium hydroxide forms sodium chlorate (I) solution which is bleach.
Write out the equation for making bleach.
2NaOH(aq) + Cl2(g) -> NaClO(aq) + NaCl(aq) + H2O(l)
Why is making bleach a disproportionation reaction?
Cl2(g) has an OS of 0
Cl in NaClO has an OS of +1
Cl in NaCl has an OS of -1
Chlorine has been simultaneously oxidised and reduced.
What are the uses of sodium chlorate (I)?
Cleaning agents as bleach
Treating water
Bleaching paper and fabrics
How can bacteria in water be killed?
By adding chlorine
What happens when chlorine is added to water
It produces chlorate (I) ions (ClO-) that kill bacteria.
What is the equation of water sterilisation?
H2O(l) + Cl2(g) <=> HClO + HCl
Why is water sterilisation a disproportionational reaction?
Cl2(g) has an OS of 0
Cl-(aq) has an OS of -1
Cl in ClO-(aq) has on OS of +1
Chlorine is being simultaneously reduced and oxidised.
What happens to water sterilisation in the presence of sunlight?
Sunlight can decompose chlorinated water but no ClO- is made.
What is the equation for water sterilisation in the presence of sunlight?
2H2O(l) + Cl2(g) -> 4H+(aq) + 2Cl-(aq) + O2(aq)
What are the advantages and disadvantages of chlorinating drinking water?
Advantages:
- Destroy diseases causing microorganisms
- Long lasting so reduces bacteria build up further down the supply
- Reduces the growth of algae which can discolour water and give it a bad taste and smell
Disadvantages:
- Chlorine gas is toxic and irritates the respiratory system
- Liquid chlorine causes severe chemical burns to the skin
- Chlorine can react with organic compounds present in the water and make chloroalkanes which have been linked to causing cancer
How can we prove the oxidising ability of group 7
Through displacement reactions
How can we prove the reducing ability of group 7?
Through
- reaction with concentrated sulfuric acid + halide ions
- reaction with silver nitrate solution + halide ions then confirm with ammonia solution
What is the rule of displacement reactions in group 7?
The more reactive halogens displace the less reactive halide ions
Describe the displacement reactions for chlorine
Cl2 - colourless
KCl + Cl2
- no reaction
KBr + Cl2
- orange solution made up of Br2 forms
- Cl2 + 2Br- —> 2Cl- + Br2
- Cl2 is more reactive than Br-
KI + Cl2
- brown solution made up of I2 forms
- Cl2 + 2I- —> 2Cl- + I2
- Cl2 is more reactive than I-
Describe the displacement reactions for bromine
KCl + Br2
- no reaction
KBr + Br2
- no reaction
KI + Br2
- brown solution made up of I2 forms
- Br2 + 2I- —> 2Br- + I2
- Br2 is more reactive than I-
Describe the displacement reactions for iodine
No reaction for all
Why do we not investigate the displacement reactions for fluorine
It would react vigorously with water
Describe what happens when conc H2SO4 reacts with Cl-
H2SO4 + NaCl -> NaHSO4 + HCl
- white misty fumes of HCl formed
Describe what happens when conc H2SO4 reacts with Br-
- Acid-base:
H2SO4 + NaCl -> NaHSO4 + HBr
Redox:
2HBr + H2SO4 -> Br2 + SO2 + 2H2O
Overall:
2NaBr + 2H2SO4 -> Na2SO4 + Br2 + SO2 + 2H2O - Br- reduces the sulfur in NaHSO4 in a redox reaction
- Br- being oxidised:
2Br- -> Br2 + 2e-
- S being reduced:
H2SO4 + 2H+ + 2e- -> SO2 + 2H20
Overall equation:
H2SO4 + 2H+ + 2Br- -> Br2 + SO2 + 2H2O
- Orange vapour of Br2 is observed
Describe what happens when conc H2SO4 reacts with I-
- Acid-base:
H2SO4 + NaCl -> NaHSO4 + HI
- HI produces steamy fumes
Redox: - I- reduces the sulfur in NaHSO4 in a redox reaction
- I- being oxidised:
2I- -> I2 + 2e-
- S being reduced:
H2SO4 + 2H+ + 2e- -> SO2 + 2H20
Overall equation:
H2SO4 + 2H+ + 2I- -> I2 + SO2 + 2H2O - SO2 reduced to S
- I- being oxidised:
6I- -> 3I2 + 6e-
- S being reduced:
H2SO4 + 6H+ + 6e- -> S + 4H2O
Overall equation:
H2SO4 + 6H+ + 6I- -> 3I2 + S + 4H2O
Yellow solid of S formed - S reduced to H2S
- I- being oxidised:
8I- -> 4I2 + 8e-
- S being reduced:
H2SO4 + 8H+ + 8e- -> H2S + 4H2O
Overall equation:
H2SO4 + 8H+ + 8I- -> 4I2 + H2S + 4H2O
Rotten egg smell of H2S
What is the method of testing halide ions with silver nitrate?
Add dilute nitric acid then silver nitrate solution, the colour of the precipitate helps identify the halide ion
Write the equations and the observations for testing halide ions with silver nitrate. What happens when we add dilute and concentrated ammonia?
(MILK, CREAM, CHEESE)
Cl-
- White ppt
- Ag+ + Cl- -> AgCl
- Dilute ammonia = white ppt dissolves
- Concentrated ammonia = white ppt dissolves
Br-
- Cream ppt
- Ag+ + Br- -> AgBr
- Dilute ammonia = no change
- Concentrated ammonia = cream ppt dissolves
I-
- Yellow ppt
- Ag+ + I- -> AgI
- Dilute ammonia = no change
- Concentrated ammonia = no change
Why do we add nitric acid when testing for halide ions with silver nitrate?
It reacts with any other anions or impurities e.g carbonates which could give a false result
