• The periodic table is arranged on the basis of atomic numbers (number of protons in the nucleus) By knowing which group an element is in, we can determine the number of reactive electrons and say something about how that element will behave.
  • Group I (alkali metals and hydrogen) elements all have one electron in their outer shell.
  • This one electron is very easily removed during chemical reactions.
  • The group I elements react rapidly with oxygen to produce metal oxides.
  • Rubidium and cesium react yet more vigorously and explode on contact with water.
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