27 November 2023

A polyatomic ion, also known by the name ‘molecular ion’, is a chemical species that is characterized by having more than one atom in its structure and by being electrically charged. The latter is attributed to the loss or gain of electrons when forming the ion.

If you are interested in the area of ​​chemistry and want to know more in depth what is a polyatomic ion, what are its characteristics, its properties and the different existing types, then you have come to the right place. Keep reading and find out with us!

Meaning of a polyatomic ion in chemistry

Polyatomic ions are a type of ion that are composed of a covalent bond that bonds two or more atoms together through a metal complex. This type of structure is usually considered a ‘single unit’ in the study of chemistry, specifically in the area of ​​the creation of bases and acids or within the formation of salts.

This type of ions are considered as a chemical species, since have an electrical charge, regardless of whether it is a molecule or an atom. This is because when they form, they need to gain or lose electrons in the chemical reaction.

What are the characteristics of polyatomic ions?

One of the main characteristics of polyatomic ions is that are considered a chemical structure in which two or more atoms are joined, through a chemical reaction that arises from a covalent bond, which is why all polyatomic ions can have both a positive charge, being called in this way with the denomination ‘cations‘, or a negative charge, which are the ‘anions‘.

The most common polyatomic ions in nature are anions, that is, where the ion has gained electrons during its formation. These electrons remain in their last valence orbital, thus being shared by the atoms that make up the ion.

In almost all polyatomic ions there is a ‘central ion’, which allows the rest to be located around it to form a structure. Almost always This type of ion is surrounded by oxygen.due to the fact that being the most abundant element on planet Earth, it is common for various molecules to arise with it.

It should be noted that when oxygen surrounds a molecule at these They are called as oxoanion, which are weak bases and react in the presence of hydrogen, thus forming acid salts. For example, this is what happens with nitric acid (HNO3).

The polyatomic ion nomenclature It depends on one main factor: with whom they react. In the event that they react with hydrogen and give their electrons to it, achieving the formation of polyatomic cations, the ending ‘ is added.onium‘. On the other hand, the modern nomenclature expresses that the oxoanions maintain the following structure: the suffix ‘ is placedI tie‘ to the name of the central element.

To differentiate between the various oxidation states of an element, the oxidation number of the atom is placed at the end, between parentheses, for example ‘Nitrate (II)’ or ‘Sulphate (VI)’.

What are the types of polyatomic ions?

There are about five types of ions within the classification, depending on how they are loaded or in what state are found in nature, which are:

  • The cations.
  • The anions.
  • The radicals.
  • The dianions.
  • The Zwitterions.

On the one hand, cations are those species that are positively charged, while anions refer to those that have a negative charge. On the other hand:

  • a dianion is that one species whose net charge is -2, that is, it has received two electrons, as for example we find pentalene. This type of ion is characterized mainly by its instability.
  • We also find the radicalswhich are a variety of polyatomic ions that have a irregular number of electrons within their structure, so they have a high instability and, therefore, are reactive.
  • a zwitterionalso known as a dipole ion, is an ion that has zero net charge, that is, it is equal to zero. In your case, it has two isolated charges in the same structure, one of which is negative and the other positive.

Notably the plasmas They could also be considered polyatomic ions, since, being gaseous fluids, the only thing that differentiates them from most ions would be their state of matter.

positive polyatomic ion

A positive polyatomic ion, known as a cation, is a very rare chemical species but very important due to the fact that it allows the formation of most metals with hydrogen (H). One of the most common polyatomic cations is ammonium (NH4). Others examples of this type of cations are:

  • Phosphonium.
  • Protonated molecular hydrogen.
  • Oxonium.

negative polyatomic ion

Negative polyatomic ions are known under the name of polyatomic anions, which are non-metallic atoms that are joined through a covalent bond and are left with a negative charge. This variety is much more common than oxoanions.

This type of anion is formed thanks to retention made by the central atom, more specifically its nucleus, towards the electrons of the other elements that make up the molecule. This is not linked due to the Coulomb forces, and instead is maintained thanks to the presence of the polarization of the neutral atom.

Generally this chemical species is obtained once protons are lost from an acidic compoundthat is, they tend to lose the H+. However, in certain structures some hydrogens are still maintained, which causes the cation to have an acidic character. For example, this can be seen in the case of bicarbonate, the phosphate group, the sulfite group, and nitrate.

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