C2 - The periodic table

• First list of elements


  • ordered by atomic mass
  • no gaps left
  • no groups of elements
  • no clear distinction between metals and non-metals
  • some elements grouped innapropriately
• Mendeleev's table


  • elements mostly ordered by atomic mass
  • some where swapped
  • gaps left for undiscovered elements
  • grouped by chemical properties
  • no clear distinction between metals and non-metals
  • incomplete
  • no explanation for why some elements needed to be swapped
• Modern Periodic Table


  • elements ordered by atomic number
  • no gaps
  • all elements up to a certain atomic number have been discovered
  • grouped by the number of electrons on their outer shells
  • metals to the left, non-metals to the right
• Group 0


  • the noble gases
  • full outer shells with eight electrons
  • do not need to gain or lose electrons
  • very unreactive (inert) so exist as single atoms
  • they do not need to bond to form molecules
  • boiling points increase down the group
• Group 1


  • all have one electron in their outer shell
  • very reactive
  • they only need to lose one electron to react
  • reactivity increases down the group
  • melting and boiling point decrease down the group
• Group 1 reactivity


  • increases down the group
  • the atoms increase in size
  • the outer electron is further away from the nucleus
  • there are more shells shielding the outer electron from the nucleus
  • the electrostatic attraction between the nucleus and the outer electron is weaker
  • this makes it easier to lose the outer electron