8.2 - The Halogens Flashcards
How many electrons do halogens have in their outer shell?
7
What is the trend in boiling points down Group 7?
- Boiling points increase.
- Because the atoms get larger, so have more electrons.
- Therefore there are stronger London forces between molecules.
What is the trend in electronegativity down Group 7?
- Electronegativity is the ability for an atom to attract electrons towards itself in a covalent bond.
- Down Group 7, electronegativity decreases because there is an increased atomic radius and more shielding due to more shells.
- There is less nuclear attraction to attract an electron from another species.
What is the trend in reactivity down Group 7?
- Reactivity in halogens decreases down Group 7.
- Oxidising power decreases down Group 7.
- Atoms with a smaller atomic radius attract electrons better than larger atoms.
What is the rule for displacement reactions in Group 7?
The more reactive halogens will displace the less reactive halide ions.
Chlorine water (Cl2) + KBr solution
Will turn orange as bromine (Br2) is made.
Chlorine has displaced bromide.
Cl2 + 2Br- → 2Cl- + Br2
Chlorine water (Cl2) + KI solution
Will turn brown as iodine made (I2).
Chlorine has displaced iodide.
Cl2 + 2I- → 2Cl- + I2
Bromine water (Br2) + KI solution
Will turn brown as iodine made (I2)
Bromine has replaced iodide.
Br2 + 2I- → 2Br- + I2
Why is there no reaction when iodine solution (I2) reacts with KCl and KBr solutions?
Iodine is less reactive than chlorine and bromine, so it does not displace them from their compounds.
What type of reaction produces bleach?
Disproportionation
What is a disproportionation reaction?
When an element is both oxidised and reduced in the same reaction.
What two substances react to make bleach?
Chlorine + cold, dilute aqueous sodium hydroxide. Forms sodium chlorate (I) solution, which is bleach.
Cl2 + 2NaOH → NaClO + NaCl + H2O
Disproportionation reaction
What is the reaction between chlorine and water?
Cl2 + H2O → HClO + HCl
How does the reaction between chlorine and water treat water?
- Chloric(I) acid (HClO) sterilises water by killing bacteria.
- HClO can further dissociate in water to form ClO- ions, which act as a sterilising agent.
What happens if universal indicator is added to the solution of chlorine + water?
- If some universal indicator is added to the solution it will first turn red due to the acidity of both reaction products. It will then turn colourless as the HClO bleaches the colour.
