For a long time, scientists tried to derive a unified theory that would explain the structure of molecules, describe their properties in relation to other substances. To do this, they had to describe the nature and structure of the atom, introduce the concepts of "valency", "electron density" and many others.
Theory of theory
The chemical structure of substances was the first to interest the Italian Amadeus Avogadro. He began to study the weight of molecules of various gases and, based on his observations, put forward a hypothesis about their structure. But he did not begin to report on it first, but he waited for his colleagues to get similar results. After that, the method of obtaining the molecular weight of gases became known as the Avogadro law.
The new theory has prompted other scientists to research. Among them were Lomonosov, Dalton, Lavoisier, Proust, Mendeleev and Butlerov.
Butlerov's theory
The formulation “theory of chemical structure” first appeared in a report on the structure of substances, which in 1861 was presented by Butlerov in Germany. It went unchanged into subsequent publications and entrenched in the annals of the history of science. This became a harbinger of several new theories. In his document, the scientist outlined his own view on the chemical structure of substances. Here are some of his points:
- atoms in molecules are connected to each other based on the number of electrons in their outer orbitals;
- a change in the sequence of the connection of atoms leads to a change in the properties of the molecule and the appearance of a new substance;
- the chemical and physical properties of substances depend not only on which atoms are included in its composition, but also on the order of their connection with each other, as well as mutual influence;
- in order to determine the molecular and atomic composition of a substance, it is necessary to carry out a chain of successive transformations.
The geometric structure of molecules
The chemical structure of atoms and molecules was supplemented three years later by Butlerov himself. He introduces the phenomenon of isomerism into science, postulating that, even having the same qualitative composition, but different structure, substances will differ from each other in a number of indicators.
Ten years later, the doctrine of the three-dimensional structure of molecules appears. It all starts with the publication by Van Goff of his theory of the Quaternary valency system in the carbon atom. Modern scientists distinguish between two areas of stereochemistry: structural and spatial.
In turn, the structural part is also divided into isomerism of the skeleton and position. This is important to consider when studying organic substances, when their qualitative composition is static, and only the number of hydrogen and carbon atoms and the sequence of their compounds in the molecule are subject to dynamics.
Spatial isomerism is necessary in those cases where there are compounds whose atoms are located in the same order, but in space the molecule is located differently. Optical isomerism is distinguished (when stereoisomers mirror each other), diastereomerism, geometric isomerism, and others.
Atoms in molecules
The classical chemical structure of a molecule implies the presence of an atom in it. It is hypothetically clear that the atom itself in a molecule can change, and its properties can also change. It depends on what other atoms surround it, the distance between them and the bonds that provide the strength of the molecule.
Modern scientists, wishing to reconcile the general theory of relativity and quantum theory, take as their initial position the fact that when a molecule is formed, an atom leaves it with only the nucleus and electrons, and itself ceases to exist. Of course, this formulation was not immediately arrived at. Several attempts were made to preserve the atom as a unit of the molecule, but all of them could not satisfy the discerning mind.
The structure, chemical composition of the cell
The concept of “composition” means the union of all substances that are involved in the formation and vital activity of a cell. This list includes almost the entire table of periodic elements:
- eighty-six elements are constantly present;
- twenty-five of them are determinate for normal life;
- about twenty more are absolutely necessary.
The five winners are discovered by oxygen, the content of which in the cell reaches seventy-five percent in each cell. It is formed during the decomposition of water, it is necessary for cellular respiration reactions and provides energy for other chemical interactions. The next most significant is carbon. It is the basis of all organic substances, and is also a substrate for photosynthesis. Hydrogen is the bronze - the most common element in the universe. It is also part of organic compounds on a par with carbon. It is an important component of water. The honorable fourth place is occupied by nitrogen, which is necessary for the formation of amino acids and, as a result, proteins, enzymes, and even vitamins.
Less popular elements, such as calcium, phosphorus, potassium, sulfur, chlorine, sodium, and magnesium, also enter the chemical structure of cells. Together, they occupy about one percent of the total substance in the cell. Trace microelements and ultramicroelements that are contained in living organisms in trace amounts.