Ion has its derivation from the Greek word ion, meaning “going”. This term was introduced by English physicist and chemist Michael Faraday in 1834 for the then-unknown species that moves from one electrode to the other through an aqueous solution .Since Faraday did not know the nature of these species, but he did know that since metals dissolved into and entered a solution at one electrode, and new metal came from a solution at the other electrode, that some kind of particles moved through the solution in a current, transferring matter from one place to the other. Faraday also introduced the words “anion” for a negatively charged ion, and “cation” for a positively charged one.
According to Faraday, cations were named because they were attracted to the cathode (the negatively charged electrode) and anions were named due to their attraction to the anode.(the positively charged electrode). The exact definition of an ion is an atom or molecule in which the total number of electrons are not equal to the total number of protons, thus the atom has a net positive or negative electrical charge.
Ions can be created by both chemical and physical process.
1.) Chemical Process : In chemical process, if a neutral atom loses one or more electrons, it has a net positive charge and is known as a cation.And if it gains electrons, it has a net negative charge and is known as an anion. An ion consisting of a single atom is called as monatomic ion and if it consists of two or more atoms, it is called a polyatomic ion.
2.) Physical Process : In the case of physical process 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. Ions are present in nature and are responsible for various phenomena ranging from the light of the Sun to the existence of the Earth's ionosphere.
Atoms in their ionic state may have a different color from neutral atoms, and thus light absorption by metal ions gives the color of gemstones. In both inorganic and organic chemistry (including biochemistry), the interaction of water and ions is extremely important; an example is the energy that drives breakdown of adenosine triphosphate (ATP).
The following sections describe contexts in which ions feature prominently; these are arranged in decreasing physical length-scale, from the astronomical to the microscopic.
Classification: An anion (−) is named after the Greek word 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).
A cation (+) is named after the Greek word meaning "down”, is an ion with fewer electrons than protons, giving it a positive charge.