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Periodic table, electron configurations. The periodic table has 118 known elements (chemical symbols) arranged by increasing atomic number to form 18 groups (vertical columns) and 7 periods (horizontal rows). Included is each element's simple electron configuration, with electrons (red) filling successive shells around the nucleus (here replaced by the chemical symbol for the element). It is the relative energy and stability of the outer electrons, and aspects of the electron configurations, that influences the chemical and physical properties of the elements. For this image with the elements colour-coded by type or 'block', see images C013/2339 and C013/2340.
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