An ion is an electrically charged atom or group of atoms. It is a part of an atom, or part of a group of atoms (molecule). It is "charged" so it will move near electricity. This is because atoms are made of three smaller parts (1) neutrons (with no charge), and equal numbers of (2) charged protons and (3) oppositely-charged electrons. An ion has unequal numbers of protons and electrons. Making an ion from an atom or molecule is called ionization.
The charge on a proton is measured as +1 (positively charged), and the charge on an electron is measured as -1 (negatively charged). An atom that is ionized makes two ions, one positive, and one negatively charged. For example, a neutral hydrogen atom has one proton and one electron. Heating the atom breaks it into two parts (1) a positively charged hydrogen ion, H+ (2) a negatively charged electron.

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