4.8 - Group 7, Halogens

• trend in atomic radius

  increases down the group because number of shells increases so takes up more space as electrons repel each other
• trend in electronegativity


  decreases down the group because atoms get bigger so more shielding & bonding electrons get further away from the nucleus so are less strongly attracted to it so can't attract bonding pairs as well
• trend in melting & boiling points

  increases down the group because number of shells increases so London forces between molecules (halogens are diatomic) get stronger so more energy is required to overcome intermolecular forces so melting & boiling points increases
• trend in reactivity


  decreases down the group because atoms get bigger so outer electrons are further away from nucleus & are shielded more due to mae innerelectrons so it's harder to attract an electron to form an ion
• where halogens are found

  never found free in nature because they're so reactive

  occur naturally as compounds with metals

  many are salts
• bonding in halogens


  diatomic molecules linked by single covalent bond
• meaning of halogen


  salt former
• solubility in water


  low solubility because they're non-polar
• solubility in organic solvents like hexane

  more soluble than in water because they're both non-polar so are attracted to each other by van der Waals dispersion forces

  attractions broken are similar to new attractions Made when they Mix
• solubility of iodine in potassium iodide solution

  reacts freely because iodine molecules react with iodide ions to form triodide ions producing yellow-brown colour

  yellow when very dilute

  dark Orange brawn when more concentrated
• appearance of fluorine at room temperature


  pale yellow gas
• colour of fluorine in water


  pale yellow
• colour of fluorine in hexane


  Colourless
• fluorine in labs


  not used because it's too dangerous
• oxidation state of fluorine

  always -1
• uses of fluorine


  make fluorocarbons

  very slippery, non-stick polymer: poly( tetrafluorethene)
• appearance of Chlorine at room temperature


  green gas
• colour of chlorine in water

  virtually colourless
• Colour of chlorine in hexane


  virtually colourless
• Oxidation state of chlorine

  usually -1

  Oxygen & fluorine can make it positive
• uses of chlorine 


  production of polymers like PVC

  bleach

  kill bacteria in drinking water
• appearance of bromine at room temperature


  red- brown liquid
• colour of bromine in water

  yellow/orange
• colour of bromine in hexane


  Orange red
• uses of bromine


  make flame retardants, medicines, dyes
• appearance of iodine at room temperature

  grey solid
• colour of iodine in water


  brown
• colour of iodine in hexane


  pink/violet
• uses of iodine


  make medicines, dyes, catalysts

  sodium iodide added to table salt & drinking water to prevent goitre ( swelling of thyroid gland)

  iodine needed in diet So thyroid can make thyroxine
• astatine


  rarest occuring halogen

  highly reactive

  most stable isotope has a half-life of just over 8 hours