Group 17

• Physical properties:

  as we descent group 7 the elements get darker

  (Yellow, green, brown, purple)

   

  • the volatility decreases because the diatomic molecules have more electrons and so greater van der waal forces are created
  • Melting point and boiling point increases
• Reactivity:

  Halogens decreases down the group and this can be shown by the way elements react with hydrogen gas

  Electronegativity increases up the group and so the ability to attract electrons and hence reactivity of the element is greater
• Reactivity

  A) reacts instantly even at -200c

  B) reacts slowly in the dark

  C) explosively when exposed to UV light

  D) requires heat then reacts slowly

  E) does not fully react (equilibrium is created)

  
• oxidising power of the halogens decrease down the group

   

  Redox or displacement reactions can occur

   

  All halogens can potentially act as oxidising agents

   

  REACTIONS —> when these reactions occur the colours of the halogens can be seen in organic solvents

  (Cl2 = purple, Br2 = brown, I2 = orange)

   
• Stability of hydrogen halides decreases as you go down the group

   

  As you go down the group, the bonds become weaker, the weaker the bond, the less heat energy you need to break it.

   
• Why is the bond weaker as you down the group of halogens?

  The halogen atoms get bigger and so the bond length is longer.

  The bonding pair of electrons is getting further from the halogen nucleus so the force of electrostatic attraction is less.
• Halide salts and sulphuric acid:

  Acts as either an oxidising agent or an acid when it reacts with halide salts

   

  • Fluoride and chloride ions are also strong oxidising agents
  • In this case the acid acts as an acid

  A) bromide and iodide salts

  B) fluoride and chloride salts

  
• • The concentrated sulphuric acid acts as an oxidising agent with bromide and iodide ions (sulphur reduced to +4 oxidation state)
  • Removes electrons from the halide ions converting the ions into the diatomic gas
  • Brown bromine gas and purple iodine gas are formed
• Reaction of chlorine with NaOH:

  Chlorine has two different reactions with NaOH depending on the conditions

   

  Both cases a DISPROPORTIONATION reaction occurs
• Uses of chlorine:

  the process of water purification

   

  An equilibrium is established

  • Reaction produced HCL the solution is too acidic so an alkali is added to keep the water at pH 7
  • Enough HOCL remains to kill any bacteria in the water

   
• Hydrogen halides dissolve in water to produce acids

  Also react with ammonia gas to produce the corresponding ammonium salt