atomic structure

• an element is a substance that contains only one form of atom
• a compound contains atoms of two or more elements, which are chemically bonded in fixed proportions
• mixtures consist of two or more elements or compounds which are not chemically combined
• group 0:

  • noble gases
  • full outer shell
  • stable electron configuration, very unreactive
  • boiling points decrease
• group 1:

  • alkali metals
  • one electron in the outer shell
  • low melting and boiling points
  • more reactive down the group
• group 7:

  • halogens
  • reactivity decreases