What does a relative charge do

A ion [i̯oːn] (from ancient Greek ἰών or ἰόνion, “Going”) is an electrically charged atom or molecule. It contains at least one positively charged atomic nucleus. Its or their charge corresponds to the number of protons it contains. An ion can also contain electrons. The outwardly effective, observable charge of the ion arises from the different numbers of protons and electrons. Ions are through electronsdefect positive, or by electronsexcess negatively charged.

Fast ionsmoving in one direction are studied or used in atomic physics, nuclear physics and particle physics, see ion radiation, ion source or particle accelerator. A plasma (e.g. inside a star) is a disordered ensemble of fast ions and electrons that move in all directions at high temperatures, like the molecules of a gas.

The following statements essentially relate to slow or stationary ions.

Positively charged ions are called cations, negatively charged anions, because they move in an electric field to the cathode (negative pole) or to the anode (positive pole). In a solvent they form a solvation shell.

Formation of Ions



Positively charged ions (Cations) are formed when atoms release electrons (usually external electrons). This creates a relative excess of protons (positive charge carriers), which is no longer balanced by the electrons present (negative charge carriers) - the positive charges predominate, the ion is positively charged!

Example:Metal ions are usually positively charged.
Equation for sodium ion formation: Na → Na+ + e
Equation for the formation of magnesium ions: Mg → Mg2+ + 2e


Negatively charged ions (Anions) are formed when atoms pick up electrons. This creates a relative excess of electrons (negative charge carriers), which is no longer balanced by the existing protons (positive charge carriers) - the negative charges predominate, the ion is negatively charged.

Example:Non-metal ions are usually negatively charged.
Equation for the formation of chloride ions: Cl + e → Cl
Equation for sulfide ion formation: S + 2e → p2−

In chemistry, mobile ions are mainly formed spontaneously when salts are dissolved in polar solvents (water) e.g. NaCl (solid) + H2O → Well+(dissolved) + Cl(dissolved), e.g. in the aqueous environment of cells and organisms (electrolyte solution). Here they play a decisive role for the electrical phenomena on membranes, especially for excitability (membrane potential, action potential).


An ion is commonly used in chemistry NiMen− (Non-metal ion) or with Men + (Metal ion).

Examples are:

  • N / A+ - sodium ion (n is omitted here, there n is equal to one)
  • S.2− - sulfide ion
  • NH4+ - Ammonium ion, a compound ion

Properties of the ions

The radius of ions differs from that of the corresponding atom. The cation radius is smaller - due to the fact that the outer orbitals are not occupied - that of the anions is usually larger because the outer orbitals are filled with electrons and / or other orbitals are newly occupied. Depending on the ratio of charge to radius, ions have different polarizing effects in chemical bonds.

Ions of different charges form salts through ionic bonding. Solutions that contain ionic substances conduct electricity and are therefore called electrolytes.

A cyclic ion is an ion that is built up in a ring structure (cyclic compounds).


Ions with more than 3 under or excess charges are rarely found in chemistry. In physics, they are generated for specific experimental purposes and also occur in nature.

Gas ions play a role in the conduction processes in fluorescent lamps and other gas discharges (electrical sparks, lightning). An (almost) completely ionized gas is called plasma.

Ionized noble gases can form ionic bonds. Noble gas halide compounds are used in excimer lasers.

In the case of molecules with two or more functional groups, it can happen that they have a positive charge on one group and a negative charge on another (the molecule is then neutral overall). Such polar molecules are also known as zwitterions.

Electrolytes play a major role in metabolic processes and in batteries.


After the release or acceptance of electrons, the valence electron shell has a different number of electrons than before. If the number of electrons of the ion in all shells is the same as the normal constellation of a noble gas atom, one speaks of a "noble gas configuration".

See also

Categories: Electrochemistry | Chemical bond