group 7- the halogens

describe the appearance of these halogens

• at room temperature and pressure

• in aqueous solutions

• F₂,CL₂, Br₂, I₂

• F₂

-room: Yellow gas

-aq: colourless solution

• CL_2-

-room: pale green gas

-aq: very pale green solution/ colourless solution

• Br_2-

-room: brown-red liquid

-aq: orange solution

• I_2-

-room: black/grey shiny solid (purple vapour)

-aq: brown solution

describe the atomic radius down group 7

• increases

• addition of new electron shells, places outer electrons further from the nucleus,

• new inner shells cause increased shielding of outer electrons from the positive nuclear charge,

• weakening the overall nuclear attraction despite more protons.

describe the trend in electronegativity down group 7

• decreases

• atomic radius increases

• shielding increases

• weaker attraction between nucleus and electrons in covalent bond

describe the trend in boiling point down group 7

• boiling point increases

• the Mr increases down the group

• the strength of VDW’s forces between molecules increases

• the energy needed to overcome IMF’s increases

state and explain the trend in oxidising ability of the halogens down group 7

• decreases

• chlorine can oxidise Br^- to Br₂

• chlorine can oxidise I^- to I₂

• bromine can oxidise I^- to I₂

what is an alternative name for the experiment that demonstrates oxidising ability of halogens

displacement

what colour are these aq halide salt solutions

• KCl

• KBr

• KI

they are colourless

what colour is a solution of-

• Cl₂

• Br₂

• I₂

• Cl₂ - colourless/ pale green solution

• Br₂ - orange solution

• I₂ - brown solution

colour changes for displacement reactions of KCl, KBr and KI with Cl_2, Br₂ and I₂

describe in words the reactions without colour changes In terms of oxidising ability of halogens

• bromine is not a strong enough oxidising agent to displace chlorine from potassium chloride (OR bromine from potassium bromide)

• iodine is not a strong enough oxidising agent o displace *halogen* from potassium chloride/bromide/iodide

• chlorine is not a strong enough oxidising agent to displace chlorine from potassium chloride

• give the balanced equations for displacement reactions of aq halide ions

• identify product responsible for colour change

• Cl₂ + 2KBr → 2KCl + Br₂

• Cl₂ + 2KI → 2KCl + I₂

• Br₂ + 2KI → 2KBr + I₂

give the ionic equations for the reactions that give colour change in halogen displacement reactions (remove spectator ions)

• Cl₂ + 2Br^- → 2Cl + Br₂

• Cl₂ + 2I^- → 2Cl + I₂

• Br₂ + 2I^- → 2Br + I₂

describe in words the reactions with colour changes In terms of oxidising ability of halogens

• chlorine is a strong enough oxidising agent to displace bromine from potassium bromide

• chlorine is a strong enough oxidising agent to displace iodine from potassium iodide

• bromine is a strong enough oxidising agent to displace iodine from potassium iodide

why is chlorine a good oxidising agent

• it is readily reduced due to its high electronegativity (little shielding, small atomic radius so strong nuclear charge)

• so it can easily accept an electron from another molecule causing it to be oxidised

describe the reaction that demonstrates the reducing ability

the reactions of solid sodium halides ( NaCl, NaBr, NaI) with concentrated sulphuric acid

state and explain the reducing ability of halide ions down the group

• increases

• down the group ionic radius increases

• so the outer electrons have weaker attraction to the nucleus so are more easily lost