ES 2

• The halogens are in group seven of the periodic table
• As electronegativity decreases going down the group of halogens

  The physical state increases
• Shielding

  The number of shells between the nucleus and the outer electrons, which reduces the effective nuclear charge
• As you go down the group of halogens, the boiling point increases due to more instantaneous dipole-induced dipole bonds
• Reactivity in halogens decreases going down group seven
• Due to the larger size and more shielding, it is difficult for iodine to attract electrons towards itself in a chemical reaction
• Halogens

  • Fluorine is a very pale yellow gas
  • Chlorine is a pale green gas
  • Bromine is a brownish-orange liquid
  • Iodine is a gray solid
• Physical state changes from gas at the top to solid at the bottom of the halogen group, showing increasing melting and boiling points
• Electronegativity

  The ability for an atom to attract electrons towards itself in a covalent bond
• For a reaction to occur, an electron needs to be gained
• Halogens involved in displacement reactions


  More reactive halogens will displace less reactive halide ions
• Formation of hydrogen halides

  Hydrogen halides are formed by adding a concentrated acid to an ionic compound
• Halide ions lose an electron in reactions and are classed as reducing agents
• As we go down the group, the ionic radius of halide ions increases, making them more powerful reducing agents
• Formation of HCl

  • By adding concentrated phosphoric acid to a salt like sodium phosphate
• Phosphoric acid is used instead of sulfuric acid due to its oxidizing properties
• Outer electrons

  Due to a weaker force, the outer electron is lost more readily, making I - a much more powerful reducing agent than F -
• Q test can be used to prove the trend with sulfuric acid and the reaction with silver nitrate solution
• Iodides are the most powerful reducing agents, reducing sulfur further to form hydrogen sulfide gas
• Stability of hydrogen halides decreases as we go down Group 7, with hydrogen fluoride and hydrogen chloride being more stable than hydrogen bromide and hydrogen iodide
• Reaction with sulfuric acid

  Produces hydrogen halides using sulfuric acid, but impurities are also formed due to sulfuric acid being an oxidizing agent
• Chloride ions do not reduce sulfur, but bromides do, forming sulfur dioxide
• Reducing agents lose electrons, making them more powerful as they can easily get rid of electrons
• Bond enthalpy decreases as we go down Group 7, with the bonding electrons being further from the nucleus, resulting in weaker attractions
• Hydrogen sulfide gas has a distinct rotten egg smell and is toxic
• Testing for chloride, bromide, and iodide ions using silver nitrate

  Add nitric acid first, then silver nitrate to observe the color of the precipitate formed
• Hydrogen halides are acidic gases that dissolve in water to form acidic solutions
• Reaction of hydrogen halides with ammonia gas

  Formation of white fumes of ammonium halides
• Shared electrons in a covalent bond are attracted by the nuclei of each of the atoms
• Chlorine is added to drinking water to sterilize it and kill harmful microorganisms
• In iodine, due to the bonding electrons being further from the nucleus, there is a weak attraction which weakens the bond
• Further testing for chloride, bromide, and iodide ions using ammonia solution

  Adding dilute ammonia to dissolve chloride precipitate, concentrated ammonia to dissolve bromide precipitate, and observing that the yellow iodide precipitate is insoluble in concentrated ammonia
• Reaction of hydrogen halides with water

  They split into ions, producing white misty fumes
• Reaction of hydrogen halides with silver nitrate

  Formation of precipitates: silver chloride for chloride ions, silver bromide for bromide ions, silver iodide for iodide ions
• High atom economies mean raw materials are used more efficiently, leading to a more sustainable manufacturing process
• Atom economy is the efficiency of a reaction, calculated as the molecular mass of the desired product divided by the sum of the molecular masses of all products, multiplied by 100
• Chlorine transported under pressure

  Makes it more economical to transport around as a liquid
• High atom economies result in less waste and fewer byproducts, saving time and money in separating undesirable products
• Chlorine is toxic and corrosive, must be kept away from skin and eyes
• Uses of chlorine

  • Sterilizing drinking water
  • Sterilizing all water in the UK
  • Killing harmful microorganisms
  • Making bleach
  • Making paper white
  • Cleaning toilets