What is an ion?

what is an ion example

Core Concepts

In this tutorial, learn what an ion is, and why it is important in chemistry.

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Ion Definition

An ion is an atom or molecule with either a positive or negative electrical charge. An ion has a charge because the number of protons does not equal the number of electrons; to find the number of protons and electrons, check out this article. This inequality comes with the addition or removal of electrons from an atom; they can be removed from neutral molecules through chemical processes or by breaking covalent bonds so the electron distribution is unequal. An example could be the reaction of a sodium atom with a chlorine atom, which forms a positive sodium cation and a negative chloride anion.

If there are more protons in an atom, it becomes a positively charged ion, or a cation. On the other hand, if there are more electrons, it is a negatively charges ion, or an anion. Since opposite charges attract each other, cations and anions usually interact to form ionic compounds.

A single charged atom counts as a monoatomic ion, while two or more atoms form a polyatomic ion. Chemists use the term “zwitterion” to refer to a net neutral molecule that has charged locations – one side of the molecule could have a positive charge while the other side has a negative charge.

zwitterion example

Chemical Formula of an Ion

The net charge of the molecule is written as a superscript after the chemical name/structure. The number comes before the sign of the charge; a cation with a charge should be written as 3+ instead of +3. Additionally, if there is a single charge, no matter if it is a cation or anion, there is no need to write a number; just write the sign indicating a positive or negative charge. Sometimes, chemists write out ions with their charges are roman numerals; this denotes which oxidation state the ion is in. For example, iron can be written as Fe(II) to denote that it is Fe2+. This can be used for monoatomic ions, not polyatomic ions.

Ion Characteristics

In their gas-like state, ions can be highly and quickly reactive with ions of the opposite charge. On the other hand, they can also occur in liquid or solid states as solvated ions; this happens when salts and solvents interact with each other, such as sodium chloride and water. These ions are more stable because they interact with the solvent, which lowers the necessity for repulsion; this changed their energy and entropy.

Depending on whether an atom is a cation or anion, it has a size difference when compared to the parent molecule; this has to do with the electrons and their repulsion energy. In a cation, there are fewer electrons than in a parent atom, so there is less repulsion energy and the electrons are held closer to the nucleus. In an anion, there are more electrons than in a parent atom, so there is more repulsion energy and the electrons are bound more loosely to the nucleus. Therefore, a cation is smaller than its parent atom while an anion is larger than its parent atom.

Ion Applications

When using high voltage or temperatures, ions can actually be produced using ion sources. This occurs in many scientific instruments and devices such as mass spectrometers, ion implanters, optical emission spectrometers, and particle accelerators.

These charged particles serve important uses beyond scientific instruments; they also have importance in household items such as smoke detectors and air purifiers. Ions can purify the air by disrupting and neutralizing the microbes in the air.

Radiation detection used the ionizing effect of gas; in X-rays, for example, an ion pair made of a positive ion and a free electron forms by the radiation of gas molecules. The instruments used to detect the ion pair has a compartment called an ionization chamber, which collects all the charges created by using an electric field.

Further Reading

Melissa Valqui