group 7

• at room temperature, chlorine is a green gas
• at room temperature, bromine is a brown liquid
• at room temperature, iodine is a grey solid
• halogens are in group 7 because they have 7 electrons in their outer shell
• halogens are:

  • non-metals
  • poor conductors of heat and electricity
  • brittle and crumbly when solid
  • toxic, corrosive and pungent
• all halogens exist as diatomic molecules, with two atoms held together by a single covalent bond
• when warmed, iodine has a purple vapour, it undergoes sublimation (solid straight to gas)
• the melting and boiling points of the halogens increase as you go down the group because:

  • they have more relative molecular mass as the molecule increases in size (more shells)
  • stronger intermolecular forces between molecules
  • requires more energy to overcome
• chemical test for chlorine:

  • damp litmus paper is bleached white when placed in chlorine
  • if blue litmus paper used, it will turn red then white