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Ion

Reviewed by Raghvendra GopalCheckmark
Last updated: July 25, 2018

What Does Ion Mean?

An ion is an atom (or group of atoms) that has gained or lost one or more electrons and has become electrically charged. There are two types of ions: anions and cations.

Ions are responsible for diverse phenomena, from the luminescence of the sun to the existence of the Earth's ionosphere. They are very important in terms of corrosion because ionic exchange is a common corrosion mechanism.

As reactive charged particles, ions are also used in air purification by disrupting microbes and in household items, such as smoke detectors.

In regards to corrosion, dissolved solids tend to exist in water in the form of ions. When these ions increase the level of electrical conductivity of the water, the electrolytes become more active, thereby increasing the rate of corrosion. The chemical and physical properties of the water also influence the rate of corrosion.

This type of corrosion can occur in underground pipes and tanks. It is called concentration cell corrosion.

Monitoring ion concentrations in water is essential for optimizing water treatment and the operation of demineralized plants. The particular techniques used in this type analysis are based on the water type and the concentration levels of corrosive ions present. (Also Read: Understanding Water Treatment and the Corrosion Control Process)

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Corrosionpedia Explains Ion

An ion is an atom that carries an electrical charge. Ions can be created by either chemical or physical means. If a neutral atom loses one or more electrons, it becomes positively charge and is known as a cation. If an atom gains electrons, it becomes negatively charged and is known as an anion. For example, when sodium (Na) loses an electron and chlorine (Cl) gains an electron, then:

The Na becomes a cation, Na+.

The Cl becomes an anion Cl.

When writing the chemical formula for an ion, its net charge is written in superscript immediately after the chemical structure for the molecule/atom.

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.

Ions in their gas-like state are highly reactive and do not occur naturally in large quantities on Earth, except in flames, lightning, electrical sparks and other plasmas. These gas-like ions rapidly interact with ions of opposite charge to produce neutral molecules or ionic salts. Ions are also produced in a liquid or solid state when salts interact with solvents (such as water) to produce solvated ions which are more stable.

If an ion contains unpaired electrons, it is called a radical ion. It is very reactive. Polyatomic ions containing oxygen, such as carbonate and sulfate, are called oxyanions. Molecular ions that contain at least one carbon-to-hydrogen bond are called organic ions.

Metal oxidation occurs at the anode corrosion cell creating metal ions and electrons. These ions migrate from the anode to the cathode via the electrolyte. The newly generated electrons move through the electrical connection from the anode to the cathode.

In wet environments, aqueous corrosion can occur due to electrochemical reactions which depend upon metal ion transportation and reaction. Gradients of metallic and electrolytic ion concentrations, temperature, ambient pressure and the presence of other metals, bacteria or active cells, all promote the corrosion rate.

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