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Ion facts for kids

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An electrostatic potential map of the nitrate ion (NO3−). The 3-dimensional shell represents a single arbitrary isopotential

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.

A liquid with ions is called an electrolyte. A gas with lots of ions is called a plasma. When ions move, it is called electricity. For example, in a wire, the metal ions do not move, but the electrons move as electricity. A positive ion and a negative ion will move together. Two ions of the same charge will move apart. When ions move they also make magnetic fields.


In chemistry, a molecule or atom that is electrically charged is called an ion. An ion has more or less electrons than there are protons in an atom. The process of giving or taking electrons away from a normal atom and turning it into an ion is called ionization.

Many ions are colourless. Elements in the main groups in the Periodic Table form colourless ions. Some ions are coloured. The transition metals usually form coloured ions.


In physics, atomic nuclei that have been completely ionized are called charged particles. These are ones in alpha radiation.

Ionization happens by giving atoms high energy. This is done using electrical voltage or by high-energy ionizing radiation or high temperature.

An ionized gas is called plasma.

A simple ion is formed from a single atom.

Polyatomic ions are formed from a lot of atoms. Polyatomic ions usually consist of all non-metal atoms, but sometimes the polyatomic ion can have a metallic atom too.

Positive ions are called cations. They are attracted to cathodes (negatively charged electrodes). (Cation is pronounced "cat eye on", not "kay shun".) All simple metal ions are cations.

Negative ions are called anions. They are attracted to anodes (positively charged electrodes). All simple non-metal ions (except H+, which is a proton) are anions (except NH4+).

Transition metals can form more than one simple cation with different charges.

Most ions have a charge of less than 4, but some can have higher charges.

Michael Faraday was the first person to write a theory about ions, in 1830. In his theory, he said what the portions of molecules were like that moved to anions or cations. Svante August Arrhenius showed how this happened. He wrote this in his doctoral dissertation in 1884 (University of Uppsala). The university did not accept his theory at first (he only just passed his degree). But in 1903, he won the Nobel Prize in Chemistry for the same idea.

In Greek ion is like the word "go". "Anion" and "cation" mean "up-goer" and "down-goer". "Anode" and "cathode" are "way up" and "way down".

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