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t-nez eNotes educator| Certified Educator

Ions are not neutral, they are by definition charged particles. Ions form when atoms gain or lose electrons. Since electrons are negatively charged, the loss of an electron results in a positive ion. As an example, sodium loses one electron to form Na+ and calcium loses two electrons to form Ca2+. These are positive ions because they now have more protons than neutrons, while neutral atoms contain an equal number of protons and electrons and therefore have a net charge of zero. (Protons are positively charged particles.) Negative ions form when an atom gains electrons, such as chlorine gaining one electron to form Cl- and oxygen gaining two electrons to form O2-. Note that atoms do not gain or lose protons, which are in the nucleus, only electrons, which are outside the nucleus.

Polyatomic ions are groups of atoms that have a net charge, such as the nitrate ion, NO3-, which consists of one nitrogen atom atom, three oxygen atoms and an extra electron.