The halogens

• These are the group 17 non-metals that are?poisonous?and include fluorine, chlorine, bromine, iodine and astatine
• Halogens are?diatomic, meaning they form molecules of?two?atoms
• All halogens have seven electrons in their outer shell
• They form?halide?ions by gaining one more electron to complete their outer shells

Colours and States at Room Temperature

Trends in physical properties of the halogens

Melting point

• The density and melting and boiling points of the halogens?increase?as you go down the group

Explaining the trend in reactivity in Group VII

• Reactivity of group 17 non-metals?decreases?as you go down the group
• The halogens electron configurations all end in?ns²np⁵
• Each outer shell contains seven electrons and when they react, they will need to gain one outer electron to get a full outer shell of electrons
• Going down the group, the?electron affinity?decreases and the?atomic radius?increases
• As you go down group 17, the number of shells of electrons?increases?so?shielding?also increases
• This means that the outer electrons are?further?from the nucleus so there are?weaker?electrostatic forces of attraction that attract the extra electron needed
• The electron is attracted less readily, so the?lower?down the element is in Group 17 the?less?reactive?it is

Reaction of the halogens with halide ions in displacement reactions

• A halogen?displacement?occurs when a?more reactive halogen displaces a?less?reactive halogen from an aqueous solution of its halide
• The reactivity of group 17 non-metals increases as you move up the group
• Out of the 3 halogens, chlorine, bromine and iodine, chlorine is the most reactive and iodine is the least reactive

Aqueous Solution Colour of Halogens

Halogen displacement reactions

Chlorine and bromine

• If you add chlorine solution to colourless potassium bromide solution, the solution becomes orange as bromine is formed
• Chlorine is?above?bromine in group 17 so it is more reactive
• Chlorine will therefore?displace?bromine from an aqueous solution of a metal bromide

2KBr (aq)? ? ? ?+?? ?Cl₂?(aq)? →? ? ?2KCl (aq) ????+????? ?Br₂(aq)

potassium bromide + chlorine → potassium chloride + bromine

Bromine and iodine

• Bromine is?above?iodine in group 17 so it is?more?reactive
• Bromine will therefore?displace?iodine from an aqueous solution of a metal iodide

Br₂?(l) +? ? ? 2NaI (aq)? ? →? ? 2NaBr (aq)? ? ?+? ? I₂?(aq)

bromine +? sodium Iodide → sodium bromide + iodine

Test yourself on halogen displacements:

Answer:

The correct option is?B.

• • Fluorine will displace chlorine as it is higher up in the group and bromine will displace iodine for the same reason.
  • Iodine is below chlorine so cannot displace chlorine from sodium chloride