An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving the atom a net positive or negative electrical charge.

Ions can be created by both chemical and physical means. In chemical terms, if a neutral atom loses one or more electrons, it has a net positive charge and is known as a cation. If an atom gains electrons, it has a net negative charge and is known as an anion. An ion consisting of a single atom is an atomic or monatomic ion; if it consists of two or more atoms, it is a molecular or polyatomic ion. In the case of physical ionization of a medium, such as a gas, what are known as "ion pairs" are created by ion impact, and each pair consists of a free electron and a positive ion.

Positive Charge And Negative Charge of Ions

Ions consist of either atoms or groups of atoms that have a charge -- either negative or positive. If they have gained electrons, they will be negatively charged, due to having more electrons than protons, and are called anions. An anion is usually composed of more than one atom. These are called polyatomic ions and are usually built around a core atom, which in most cases is a non-metal.


Anions are atoms that have gained electrons. Since they now have more electrons than protons, anions have a negative charge.

Anions are one of the two types of ions. The other type is called a cation, and these have a positive charge. Ions are atoms that have an electrical charge.

Anions are termed so because they get attracted towards the Anode(the positive electrode).

Anion Definition: An ionic species having a negative charge.

An anion (−) (pron.: /ˈæn.aɪ.ən/ an-eye-ən), from the Greek word ἄνω (ánō), meaning "up", is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively charged and protons are positively charged).


Anions And Cation


The hydrogen atom (center) contains a single proton and a single electron. Removal of the electron gives a cation (left), whereas addition of an electron gives an anion (right). The hydrogen anion, with its loosely held two-electron cloud, has a larger radius than the neutral atom, which in turn is much larger than the bare proton of the cation. Hydrogen forms the only cation that has no electrons, but even cations that (unlike hydrogen) still retain one or more electrons are still smaller than the neutral atoms or molecules from which they are derived.

Common anions include acetate, bromide, hydroxide, carbonate, chlorate, chloride, chromate, cyanide, fluoride, nitride, nitrate, sulphite, phosphate and oxide. Except for hydroxide and cyanide, all anions that end in –ide are monatomic. Group 7 atoms called halides, which include such elements as fluorine, chlorine, bromine and iodine, form anions with their charge of negative one. Elements such as oxygen and sulfur carry a charge of negative two, while nitrogen and phosphorus carry a negative three charge. All of these combine with an atom to form an anion. Most polyatomic ions combine with oxygen and/or hydrogen to make an anion. In polyatomic ions, the negative charge, or electron, is shared around the entire ion, not within a specific nucleus in the ion. Anions are also known as negative ions, while positive ions are called cations. Cations are atoms that have lost an electron, and as a result, they have a positive charge. Cations and anions are often found in water because of the nature of the water molecule.