Nuclear Power Plant Isar, Germany

Spent nuclear fuel pool

Turbine of a nuclear plant



In physics and chemistry, an ion is an atom or molecule that does not have a neutral electrical charge. An ion with a positive electric charge is called cation, and an ion with a negative electric charge is anion.

The process of gaining or losing electrons (with respect to the neutral atom or molecule) is called ionization. Cations and anions are usually represented with the corresponding atom symbol and the "+" or "-" symbol, respectively. If the number of electrons won or lost is greater than one, this is also indicated.

The cations and anions are attracted to the cathode and anode, respectively.

Michael Faraday was the first to propose the existence of ions, in 1830, but it was Arrhenius who developed the corresponding theory in 1884. This earned him the Nobel Prize in Chemistry in 1903.


The phenomenon that follows an atom loses or gains one or more electrons is called ionization. In physics, fully ionized atoms, such as those of alpha particles, are commonly called charged particles. Ionization is generally performed by applying high energy to atoms, in the form of electrical potential or radiation. An ionized gas is called plasma.

Negatively charged ions are known as anions (which are attracted to anodes) and positively charged ions are called cations (and are attracted to cathodes). The ions are divided into monoatomics and polyatomomics.

Ionization energy

For individual atoms in a vacuum, there is a physical constant associated with the ionization process. The energy required to remove electrons from an atom is called ionization energy or ionization potential. These terms are also used to describe the ionization of molecules and solids, but the values ​​are not constant, since the ionization is influenced by local chemical bonds, geometry and temperature.

The ionization energy decreases along a group of periodic tables, and increases from left to right throughout the period. These tendencies are exactly opposite to those of the atomic ray, this because, since the purpose of an atom is to form an octet (thanks to the valence electrons), then it moves more towards the groups on the right of the periodic table (towards the "noble gases" ") we find atoms with a high ionization energy value.

It is called first ionization energy, the energy required to remove an electron, second ionization energy that is required to remove two electrons, and so on. Subsequent ionization energies are always significantly larger than the previous ones. This is why ions tend to form in certain ways. For example, sodium is found as Na +, but usually not as Na 2+, due to the high second ionization energy required, which is much higher than the first ionization energy. Similarly, magnesium is found as Mg 2+ and not Mg 3+, and aluminum exists as a cation 3+

Generally, ionization potentials decrease from top to bottom, and grow from left to right in the periodic table. This trend is the opposite of that found for the atomic radius. This is because, in small atoms, electrons are more strongly attracted to the nucleus and there is more energy to start them.

The first ionization potential is what is needed to start the first electron of a neutral atom; the second potential is that which is needed to start two electrons, and so on. Ionization potentials gradually increase. Generally, there is a considerable leap of energy at some point in the series. This causes each atom to tend to form a certain type of cation.

Ionizing radiation

Ionizing radiations are those that have a frequency large enough to ionize the atoms or molecules of the exposed substances. This type of radiation is capable of modifying the chemical structure of the substances on which they affect and can produce long-term biological effects on living beings.

An example of ionizing radiation would be the modification of the DNA of the cells, these DNA mutations can lead to cancer. X-rays and gamma radiation would be two examples of highly ionizing electromagnetic radiation.

Non-ionizing radiation

Non-ionizing radiations are those that do not have enough frequency to cause ionization of the exposed materials. As an example of non- ionizing radiation, microwave or radio waves can be mentioned.

This type of radiation does not have enough energy to directly cause DNA mutations and, therefore, probably cannot initiate carcinogenesis but could be promoters. Today we talk about electromagnetic pollution to refer to the exposure of living beings or devices to an electromagnetic field and the effects of this exposure on health or fertility are discussed.

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Last review: August 29, 2019