Group 7 - halogens

What is the trend in ELECTRONEGATIVITY down group 7 [3]?

• Decreases.

• Atomic radius increases, shielding increases.

• Attraction between the nucleus and electron pair decreases.

What is the trend in BOILING POINTS down group 7 [3]?

• Increases.

• Atomic radius increases.

• There are more electrons, so more and stronger van der waals forces, so more energy is needed to break these bonds.

What is the trend in OXIDISING ABILITY down group 7 [3]?

• Decreases.

• Atomic radius increases, shielding increases.

• Attraction between the outer electron and nucleus decrease, so the halogen is less able to gain electrons.

What is the trend in REDUCING ABILITY down group 7 [3]?

• Increases.

• Atomic radius increases, shielding increases.

• Outer electron is further from the nucleus so the electrostatic force of attraction is weaker and the ion can lose electrons more easily.

What is the test for halides [3]? Why are those solutions used? And what are the results [3]?

Sample + nitric acid (to remove carbonate & hydroxide ions to prevent false positives) + silver nitrate (produces distinct different coloured halide ions) + ammonia (confirms the halide precipitates based on their solubility) → silver halide

• Silver chloride = a white precipitate

• Silver bromide = a cream precipitate

• Silver iodide = a yellow precipitate

What is the trend in SOLUBILITY of SILVER HALIDES down the group [3]?

• Decreases.

• Ions get larger, polarity decreases.

• Silver-halide bond gets stronger, making it more difficult for ammonia to break the bond.

What are the reactions [2] for chlorine and water?

Reversible disproportionation reaction:

• Cl2 + H2O → HCl + HClO

Decomposition reaction:

• 2Cl2 + H2O → 4HCl + O2 (In sunlight or heat)

What are the uses [4] of the disproportionation reaction of chlorine and water? What are the cons [3]?

The disproportionation reaction produces hypochlorus acid which disinfects water by killing microorganisms, prevents waterborne diseases, is long lasting and reduces the growth of algae.

• CONS: Cl2 is toxic + dangerous, ‘chlorinated water' could affect aquatic life if released into oceans and it can react with organic matter and become a risk factor for cancer.

What is produced when chlorine reacts with NaOH? What are the conditions required [3]? And what is the products made used for [2]?

• Cl2 + 2NaOH → NaCl + NaClO + H2O

• NaOH must be cold, dilute and aqueous.

• Sodium chlorate produced is bleach, its used as a disinfectant and bleaching agent to whiten clothes.

What are the natural states and colours of: F2, Cl2, Br2 & I2?

• Fluorine: pale yellow gas.

• Chlorine: pale green gas.

• Bromine: orange-brown liquid.

• Iodine: grey solid.

What are the products of Sodium-HALIDE with sulfuric acid? And why are only NaBr and NaI redox reactions [3]?

• NaF + H2SO4 → NaHSO4 + HF

• NaCl + H2SO4 → NaHSO4 + HCl

• NaBr + H2SO4 → NaHSO4 + HBr, + Br2 + SO2 + 2H2O

• NaI + H2SO4 → NaHSO4 + HI, + I2 + SO2 + 2H2O + S + H2S

NaBr & NaI are redox as the oxidation state of S changes.

• In NaBr, S's state changes from: +6 to +4

• In NaI, S's state changes from: +6 to +4 to 0 to -2

What would you see when aqueous chlorine [2], bromine [2] and iodine water is added to aqueous potassium iodide solution?

• Chlorine: Brown solution, Cl has displaced I

• Bromine: Brown solution, Br has displaced I

• Iodine: Brown solution (no reaction)

What would you see when aqueous chlorine [2], bromine and iodine water is added to aqueous potassium bromide solution?

• Chlorine: Yellow solution, Cl has displaced Br

• Bromine: Yellow solution (no reaction)

• Iodine: Brown solution (no reaction)

What would you see when aqueous chlorine, bromine and iodine water is added to aqueous potassium chloride solution?

• Chlorine: Very pale green (no reaction)

• Bromine: Yellow solution (no reaction)

• Iodine: Brown solution (no reaction)