3. Lithium Through Neon   Previous PageNext Page
     Gain and Loss of Electrons: Ionization Energy

Atoms interact with one another to form bonds in molecules by gaining, losing, or sharing electrons. A key idea in chemistry is the great stability of filled electron shells around an atom. Since lithium has only one electron outside a filled helium core, it can lose that electron easily and become a positively charged ion:

lithium atomlithium ion

This ionization is shown schematically opposite(top). Much more energy would be needed to remove electrons from the first or inner shell, and this ordinarily does not happen in chemical reactions. A beryllium atom, with two electrons outside the closed helium shell, can lose both electrons to become a doubly charged ion, as shown opposite(middle):

beryllium atomberyllium ion

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