CHON: COMMON CHARACTERISTICS, PECULIARITIES AND MOLECULES - CHEMISTRY - 2025

CHON: C carbon, H hydrogen, O oxygen and N nitrogen, are a group of chemical elements that make up living matter. Due to their location on the periodic table, these atoms share characteristics that make them suitable for forming organic and covalent molecules.

These four chemical elements make up most of the molecules of living beings, called bioelements or biogenic elements. They belong to the group of primary or main bioelements because they are 95% in the molecules of living beings.

Source: Gabriel Bolívar

The CHON molecules and atoms are shown in the upper image: a hexagonal ring as a molecular unit in carbon; the H ₂ molecule (green in color); the diatomic molecule of O ₂ (colored blue); and the diatomic molecule of N ₂ (red), with its triple bond.

They have, apart from the common properties, some peculiarities or characteristics that explain why they are suitable for forming biomolecules. By having a low atomic weight or mass, this makes them very electronegative and they form stable, strong, high-energy covalent bonds.

They bind together forming part of the structure of organic biomolecules such as proteins, carbohydrates, lipids and nucleic acids. They also participate in the formation of inorganic molecules essential for life to exist; such as water, H ₂ O.

CHON Common Features

Low atomic mass

They have a low atomic mass. The atomic masses of C, H, O and N are: 12u, 1u, 16u and 14u. This causes them to have a smaller atomic radius, which in turn allows them to establish stable and strong covalent bonds.

Covalent bonds are formed when the atoms that participate to form the molecules share their valence electrons.

Having a low atomic mass, and therefore a lower atomic radius, makes these atoms very electronegative.

High electronegativity

C, H, O, and N are highly electronegative: they strongly attract the electrons they share when they form bonds within a molecule.

All the common properties described for these chemical elements are favorable for the stability and strength of the covalent bonds that they form.

The covalent bonds that they form can be apolar, when the same elements join, forming diatomic molecules such as O ₂. They can also be polar (or relatively polar) when one of the atoms is more electronegative than the other, as in the case of O with respect to H.

These chemical elements have a movement between living beings and the environment known as the biogeochemical cycle in nature.

Special features

Some particularities or properties possessed by each of these chemical elements that give reason for its structural function of biomolecules are mentioned below.

The carbon atom C

-Because of its tetravalence, C can form 4 bonds with 4 different or equal elements, forming a great variety of organic molecules.

-It can be attached to other carbon atoms forming long chains, which can be linear or branched.

-It can also form cyclic or closed molecules.

-It can form molecules with single, double or triple bonds. If there is pure H in the structure in addition to C, then we speak of hydrocarbons: alkanes, alkenes and alkynes, respectively.

-By joining with O, or N, the bond acquires polarity, which facilitates the solubility of the molecules it originates.

-By combining with other atoms such as O, H and N, it forms different families of organic molecules. It can form aldehydes, ketones, alcohols, carboxylic acids, amines, ethers, esters, among other compounds.

-Organic molecules will have different spatial conformation, which will be related to the functionality or biological activity.

The H atom

-It has the lowest atomic number of all chemical elements, and combines with O to form water.

-This H atom is present in a large proportion in the carbon skeletons that form organic molecules.

-The greater the amount of CH bonds in the biomolecules, the greater the energy produced with their oxidation. For this reason, the oxidation of fatty acids generates more energy than that produced in the catabolism of carbohydrates.

The O atom

It is the bioelement that together with H form water. Oxygen is more electronegative than hydrogen, which allows it to form dipoles in the water molecule.

These dipoles facilitate the formation of strong interactions, called hydrogen bonds. Weak bonds such as H bridges are essential for molecular solubility and for maintaining the structure of biomolecules.

The N atom

-It is found in the amino group of amino acids, and in the variable group of some amino acids such as histidine, among others.

-It is essential for the formation of amino sugars, the nitrogenous bases of nucleotides, coenzymes, among other organic molecules.

Molecules that make up CHON

Water

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H and O are joined by covalent bonds, forming water in a proportion of 2H and O. Because oxygen is more electronegative than hydrogen, they join together to form a polar-type covalent bond.

By having this type of covalent bond, it allows many substances to be soluble by forming hydrogen bonds with them. Water is about 70 to 80% part of the structure of an organism or living being.

Water is the universal solvent, it fulfills many functions in nature and in living beings; it has structural, metabolic and regulatory functions. In an aqueous medium, most of the chemical reactions of living beings are carried out, among many other functions.

The gases

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By union of the apolar covalent type, that is, without difference in electronegativity, equal atoms such as O are united. Thus, atmospheric gases are formed, such as nitrogen and molecular oxygen, essential for the environment and living beings.

Biomolecules

Source: Max Pixel

These bioelements unite with each other, and with other bioelements, forming the molecules of living beings.

They are joined by covalent bonds, giving rise to monomeric units or simple organic molecules. These in turn are joined by covalent bonds and form complex organic molecules or polymers and supramolecules.

Thus, amino acids form proteins, and monosaccharides are the structural units of carbohydrates or carbohydrates. Fatty acids and glycerol make up saponifiable lipids, and mononucleotides make up nucleic acids DNA and RNA.

Among the supramolécules are, for example: glycolipids, phospholipids, glycoproteins, lipoproteins, among others.

References

1. Carey F. (2006). Organic Chemistry. (6th ed.). Mexico, Mc Graw Hill.
2. Course Hero. (2018). 2 function of bio elements bioelements primary among. Recovered from: coursehero.com
3. Cronodon. (sf). Bioelements. Recovered from: cronodon.com
4. Life Person. (2018). Bioelements: Classification (Primary and Secondary). Recovered from: lifepersona.com
5. Mathews, Holde and Ahern. (2002). Biochemistry (3rd ed.). Madrid: PEARSON