Atom's structure

What Is an Ion? Anions and Cations

What is an ion? Anions and cations

An ion is a charged atom or group of atoms ( molecular ions); it does not have a neutral electric charge. A cation is a positively charged ion, and an anion is a negatively charged one (atom or molecule). So, these chemical species may be positive or negative.

Ions are formed when atoms lose or gain electrons. Anions have more electrons than protons, and cations have a number of protons higher.

There are two kinds of ions: anions and cations. Cations and anions are represented with the symbol of the corresponding atom and the character "+" (cations) or "-" (anions).

If the number of electrons gained or lost is more significant than one is also indicated.

There are two types of ions:

  • Monatomic ions consist of a single atom.

  • Polyatomic ions are ions consisting of two or more atoms.

Chemical formulas for ionic compounds are called ionic formulas. The ionic formula has a cation and an anion in it, but never two of the same type. The rule is simple: the total positive charge must balance the full negative charge.

What Are Anions and Cations? Ion Types

There are two types:

  • Negatively charged ions are anions. The anodes attract them.

  • Cations are ions with a charge positive. They are attracted to the cathodes.

The cations are attracted to the cathode. Anions are attracted to the anode.

The Anode and Cathode

A cathode is an electrode that undergoes a reduction reaction, whereby a material reduces its oxidation state by receiving electrons.

The anode is an electrode in which an oxidation reaction occurs. Through this reaction, a material, by losing electrons, increases its oxidation state.

What Is Ionization Energy?

Ionization energy is the energy required to remove electrons from an atom. Also called ionization potential.

Ionization is the phenomenon by which the number of electrons of an atom changes. It may lose or gains one or more electrons.

Ionization occurs by applying high energy to atoms in the form of electric potential or radiation.

For individual atoms in a vacuum, there is a physical constant linked with the ionization process. Local chemical bonds, geometry, and temperature influence ionization.

First Ionization Energy

First ionization energy is the energy required to remove an electron.

The second one is needed to remove two electrons. Ensuing ionization energies are always relatively larger than previous ones.

Ionization potentials are gradually increasing. Generally, there is a massive jump in energy at some point in the series. It causes each atom to tend to form a specific type of cation.


For example, the sodium atom is found as Na +, but not generally as Na 2+. It is due to the high second required energy that it is much higher than the first.

Similarly, magnesium is found as Mg 2+ and not Mg 3+, and aluminum exists as a 3+ cation.

These potentials decrease from top to bottom. They grow from left to right on the periodic table. This trend is inverse of that found for the atomic radius.

What is an ion? Anions and cations

It is because, in small atoms, the electrons are more strongly attracted to the nucleus.


Published: September 7, 2015
Last review: October 23, 2020