Explained in a different way, the ionization of an atom or a molecule consists in the emission of an electric charge in order to modify the electric polarization of these, which originally is neutral. This modification phenomenon is caused by the loss or gain of an electron.
When an atom or molecule gains an electron, it becomes negatively charged and is categorized as an anion. If, on the contrary, the molecule or atom loses an electron, it becomes positively charged and is categorized as a cation.
The chemical reaction of ionization can occur via liquids, gases or solids. When it occurs in a liquid form, the electric charge imposed on the electrons gives them sufficient energy to break its bond (ionic or covalent). For example, when HCl is added to water, the ionization of the molecules is activated and produces a mixture of H3O and Cl- .
During ionization, the energy required to separate an electron from a neutral atom/molecule is equal to the ionic energy of said atoms/molecules. Thus, it is easier to separate electrons from atoms with low ionic energy such as alkali metals since they have single valence electrons. This is why it is more common to find alkali metal cations like sodium (NaCl)
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