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Difference between Cation and Anion

Cation and anion are two types of ions which are formed when an atom or molecule loses or gains electrons respectively. In other words, when an atom loses or gains one or more electrons it turns into a charged particle which is known as an ion. Let us understand an atom to have a clear idea of how ions are formed.

Everything is made up of matter and an atom is the smallest particle of the matter, so everything in the universe is made of atoms. An atom is made up of protons, neutrons and electrons. Protons and neutrons are contained in the nucleus of the atom and electrons revolve around the nucleus. Protons are positively charged particles, they carry the positive charge and electrons are negatively charged particles, they carry the negative charge. Neutrons are neutral, they don?t carry any charge.

An atom has an equal number of protons and electrons. So, when an atom gains one or more electrons, it has more electrons than protons so it acquires the negative charge and is known as an anion (ion with a negative charge). Similarly, when an atom loses electrons, it has more protons than electrons which gives it a net positive charge and is known as a cation (ion with a positive charge). Let us see how cation differs from anion!

Cation:

It is a positively charged Ion. It is formed when an atom loses one or more electrons. An atom has an equal number of protons and electrons when it loses electrons, the protons outnumber the number of electrons which gives it a net positive charge. A cation is smaller in size than its parent atom as with the decrease in the number of electrons the repulsive power of electron is reduced and the power of protons to attract the electrons towards the nucleus increases which reduces the radius of the cation.

The positive charge of the cation is represented by the positive (+) sign. For example, Na+ indicates the cation has one electron less than the protons; similarly a cation with '+3' charge has three electrons less than the total number of protons.

Cations travel towards the cathode (negative electrode) during electrolysis and they are generally formed by metal atoms in an attempt to acquire the noble gas configuration, e.g. the formation of a hydrogen ion from a hydrogen atom: H ? e- → H+

Anion:

It is a negatively charged Ion. It is formed when an atom gains one or more electrons. An atom has an equal number of protons and electrons, so when it gains electrons the number of electrons exceeds the number of protons which gives it a net negative charge. An anion is larger in size than its parent atom as with the increase in the number electrons, the electron-electron repulsion increases and repels electrons further apart which increases the radius of the anion.

The negative charge of the anion is represented by the negative (-) sign. For example, Cl- indicates that it has one electron more than the total number of protons; similarly an anion S2- has two electrons more than the total number of protons.

Anions travel towards the anode (positive electrode) during electrolysis and they are generally formed by non-metal atoms in order to acquire noble gas configuration, e.g. the formation of an iodine anion from an iodine atom: I + e- → I-

Based on the above information, some of the key differences between cation and anion are as follows:

Cation Anion
It is a positively charged ion, e.g. Na+, Fe2+, Pb2+ etc. It is a negatively charged ion, e.g. Cl-, F-, OH- etc.
It has more protons than electrons. It has more electrons than protons.
It migrates towards anode during electrolysis. It migrates towards cathode during electrolysis.
It gains electrons from the cathode and becomes a neutral atom. It loses electrons to the anode to become a neutral atom.
It is formed from metal atoms and is smaller in size than its parent atom. It is formed from non-metal atoms and is larger in size than its parent atom.
Cations undergo electrostatic interaction with anions to form ionic compounds. Anions undergo electrostatic interactions with cations to form ionic compounds.
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