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

• Red/Brown 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^-

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-

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