the periodic table

• what are periods?

  • horizontal rows that show the number of shells of electrons
  • numbered from 1-7
  • e.g. elements in period 2 have two electron shells
• what are groups?

  • vertical columns that show how many outer electrons each atom has
  • numbered from 1-7, final group is called group 0 (instead of 8)
  • e.g. group 4 elements have atoms with 4 electrons in the outermost shell