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<-   The atoms   ->
Tableau périodique des éléments
images/mendeleiev.gif
Periodic table of the elements, or Mendeleiev table, where the atoms are lined up by increasing mass.
Copyright : Paris Observatory / UFE

All atoms are made up of a nuclei (protons and neutrons) surrounded by electrons. In an atom at rest, the number of electrons is equal to the number of protons. For instance, the oxygen atom has 8 protons and 8 electrons. These numbers are given in the element chart.

There are 113 chemical elements (atoms), which represent all the possible combinations between protons, electrons and neutrons. The heavier atoms are unstable and have very short lifetimes.