Group 7-Halogens

What do group 7 elements exist as ?

• Diatomic molecules

• I.e 2 atoms sharing electrons in a covalent bond

What happens to atomic radius down group 7?

• Increases

What colour and state is F₂

• Pale yellow gas

What colour and sate is Cl₂

• Green gas

What colour and sate is Br₂

• Brown/ Red liquid

What colour and sate is I₂

• Grey solid

What happens to electronegativity down G7 and why

• Electronegativity decreases

• Atomic radius increases/increased shielding

• Weaker attraction between nucleus and shared electrons in covalent bond

What happens to BP down G7 and why

• Increases

• Halogen molecules get larger

• VDWS forces between molecules increase

-Strength of VDWs influences BP and thus the state of the halogens at room temp

What is oxidising ability ?

• Power to take electrons

• As oxidising agents get reduced i.e accept electrons

What happens to the oxidising ability of the halogens as you go down G7 and why

• Decreases

• Atom radius increases /increased shielding

• Electrons gained less easily

Best oxidising agent

• Fluorine

What happens in a displacement reaction

• A halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of its compounds.

What happens when you add chlorine to NaBr give equations

• Cl better oxidising agent than Br

• Orange solution forms →As Bromide has been displaced/oxidised

• 2Br^- → Br₂ +2e^-

• Cl₂ +2e^- → 2Cl^-

Full ionic equation Cl₂ + 2Br ^- → 2Cl^- + Br₂

What happens when you add Cl₂ to NaI and give equations

• Chlorine better oxidising agent than iodine

• Brown solution forms →As Iodide has been oxidised

• 2I^- → I₂ +2e^-

• Cl₂ +2e^-—>2Cl-

Full ionic equation; Cl₂ +2I^- →2Cl- + I₂

What is bleach used in?

• Water treatment

• Cleaning

• Textiles

How do you make NaClO ? i.e used in bleach

• React Cl₂ with cold dilute NaOH

Equation for producing NaClO

• 2NaOH + Cl₂ →NaClO + NaCl + H₂O

• ClO^- is what kills the bacteria

What type of reaction is the production of NaClO?

• Disproportionation reaction

What happens in a disproportionation reaction

• One substance is being oxidised and reduced simultaneously

What is being reduced and oxidised at the same time in the production of NaClO

• Cl₂

• One chlorine atom is being oxidised the other reduced

Equation for Cl₂ reacting with water and the significance of the product

• ClO^- produced which kills bacteria in water

• Also prevents growth of algae →removing any bad tastes and smell

• Is a disproportionation reaction

What’s the cons of reacting chlorine with water?

• Chlorine gas can irritate respiratory system and as a liquid it can cause chemical burns

• The benefits to health of water treatment by chlorine outweigh its toxic effects.

What happens to chlorine in sunlight ?

• It decomposes

• This must be prevented when we react it with water →Otherwise you’ll get a different reaction

What reaction occurs when you react chlorine with water in the presence of sunlight

• Cl2 doesn’t undergo the disproportionation reaction

What is the reagent used to test for halides?

• Acidified silver nitrate

Why is silver nitrate acidified using nitric acid when testing for halide ions? give equation

• Nitric acid will react with impurities

• Such as carbonate ions

• As they will also react with Silver nitrate producing ppt

• Impurities will be released as gas

2H⁺ + CO₃^2- →CO₂ +H₂O (H+ comes from ntirc acid)

What happens when you add silver nitrate to test for fluoride ions ?

• No visible change

What colour ppt do chloride ,bromide and iodide ions form ?

• White = chloride

• Cream =bromide

• Yellow=iodide

What is the follow up test used to test for halide ions and why is it used

• Ammonia solution is used

• Colours of the ppt are difficult to differentiate

What ppt will dissolve in dilute ammonia solution

• AgCl

What ppt will dissolve in conc ammonia solution

• AgBr

What ppt doesn’t dissolve at all in ammonia solution

AgI

What is reducing power?

• Ability to donate electrons

• As reducing agents gets oxidises

What happens to reducing power of halide ions as you go down group 7 and why

• Increases

• Ions get bigger

• Attraction between nucleus and outer electrons decreases due to increased shielding

• Electrons lost more easily

What is produced when Halide salts react with concentrated sulfuric acid?

• Sodium hydrogen sulfate/NaHSO₄

• Hydrogen halide e.g HCl or HBr or HI

• (These reactions with sulfuric acid prove the pattern of reducing ability)

What is the equation of NaF reacting with conc H₂SO₄ and the observations

• White steamy fumes of HF

• F^- is not a strong enough reducing agent to reduce S in H₂SO₄

• So this is not a redox reaction

What is the equation of NaCl reacting with H₂SO₄ and observations

• White steamy fumes of HCl

• Cl- ion is not a strong enough reducing agent to reduce the S in H₂SO₄

• So this not a redox reaction

What type of reaction occurs when NaF or NaCl reacts with H₂SO₄

• Acid base reaction

• H₂SO₄ acts as a proton donor

What equations occur when you react NaBr with H₂SO₄ -observations

• 2Br^- → Br₂ + 2e^-

• H2SO4 + 2H+ + 2e- → SO₂ + 2H₂O

• Combine the 2 equations to get the full redox equation

-Orange fumes as 2Br^- is oxidised into Br₂

-SO₂ is a choking gas

How do u test for SO₂

• Use filter paper soaked in K₂Cr₂O₇

• Will change from orange to green

What happens Iodide ions react with sulfuric acid

• I- can reduce the sulfur to produce 3 different Sulfur containing compounds

• Because I^- is an extremely good reducing agent

What is the reaction for Iodide ion reducing S from H₂SO₄ into SO2

• H₂SO₄ → SO₂

• 2I- → I₂

• Combine to get full equation

• I₂ produced will either be a grey solid or purple gas

Reaction of I^- reducing Sulfur in H₂SO₄ into S

• H₂SO₄ → S

• 2I- → I₂

• Combine to get full equation

• Sulfur produced is a yellow solid

Reaction of I- reducing the S in H₂SO₄ into H₂S

• H₂SO₄ → H₂S

• 2I- → I₂

• Combine to get full equation

• H2S has a rotten egg smell

What happens when you add Br₂ to NaI and give equations

• Bromine will displace Iodide ions