For a long time, scientists tried to develop 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 "valence", "electron density" and many others.
The background of the creation of the theory
The chemical structure of substances first interested the Italian Amadeus Avogadro. He began to study the weight of the molecules of various gases and, based on his observations, put forward a hypothesis about their structure. But he was not the first to report on it, but waited until his colleagues received similar results. After that, the way to get the molecular weight of gases became known as Avogadro's Law.
The new theory prompted other scientists to study. Among them were Lomonosov, D alton, Lavoisier, Proust, Mendeleev and Butlerov.
Butlerov's theory
The wording "theory of chemical structure" first appeared in a report on the structure of substances, which Butlerov presented in Germany in 1861. It was included without changes in subsequent publications andentrenched in the annals of the history of science. This was the forerunner of several new theories. In his document, the scientist outlined his own view on the chemical structure of substances. Here are some of his theses:
- atoms in molecules are connected to each other based on the number of electrons in their outer orbitals;
- a change in the sequence of connection of atoms leads to a change in the properties of the molecule and the appearance of a new substance;
- chemical and the physical properties of substances depend not only on which atoms are included in its composition, but also on the order of their connection to each other, as well as mutual influence;- in order to determine the molecular and atomic composition of a substance, it is necessary to draw a chain of successive transformations.
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't Hoff of his theory of the quaternary system of valences 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 take into account when studying organic substances, when their qualitative composition is static, and onlythe number of hydrogen and carbon atoms and the sequence of their compounds in the molecule.
Spatial isomerism is necessary when there are compounds whose atoms are arranged in the same order, but in space the molecule is located differently. Allocate optical isomerism (when stereoisomers mirror each other), diasteriomerism, geometric isomerism and others.
Atoms in molecules
The classical chemical structure of a molecule implies the presence of an atom in it. Hypothetically, it is 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, accept as the initial position the fact that when a molecule is formed, an atom leaves only a nucleus and electrons for it, and itself ceases to exist. Of course, this formulation was not reached immediately. Several attempts have been made to preserve the atom as a unit of the molecule, but they have all failed to satisfy discerning minds.
Structure, chemical composition of the cell
The concept of "composition" means the union of all substances that are involved in the formation and life of the cell. This list includes almost the entire table of periodic elements:
- eighty-six elements are always present;
- twenty-five of them are deterministic for normallife;- about twenty more are absolutely necessary.
The top five winners are opened by oxygen, the content of which in the cell reaches seventy-five percent in each cell. It is formed during the decomposition of water, is necessary for cellular respiration reactions and provides energy for other chemical interactions. Next in importance is carbon. It is the basis of all organic substances, and is also a substrate for photosynthesis. Bronze gets hydrogen - the most common element in the universe. It is also included in organic compounds on the same level as carbon. It is an important constituent 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.
The chemical structure of the cell also includes less popular elements such as calcium, phosphorus, potassium, sulfur, chlorine, sodium and magnesium. Together they occupy about one percent of the total amount of matter in the cell. Microelements and ultramicroelements are also isolated, which are found in living organisms in trace amounts.
