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A definition and a subject of chemistry

Chemistry is the science of substances, their structure, properties and transformations, as well as the phenomena that accompany these transformations.

The great Russian scientist M.V. Lomonosov, one of the founders of chemistry as a science, gave the following definition of chemistry: “Chemistry is the science of changes occurring in a mixed body, since it is mixed. … Since it is customary in science to prove what is asserted, then in chemistry everything that is stated must be proved.

According to the definition of the great Russian chemist D. I. Mendeleev, “chemistry in its modern state can … be called the doctrine of the elements.”

Chemistry refers to the natural sciences that study nature and the world around us. Modern chemistry, in contact with other natural sciences (physics, biology, geology), gives rise to many branches of modern science: physical chemistry, chemical physics, biochemistry, geochemistry, etc. In addition, mathematical apparatus is used to describe chemical laws, and theoretical chemistry cannot be developed without mathematics.

Historically, two main branches of chemistry have evolved: inorganic chemistry (studying chemical elements and the simple and complex substances they form) and organic chemistry (studying compounds of carbon with other elements (organic substances)). Today, modern chemistry is also represented by other independent branches, the most important of which are physical chemistry, chemistry of macromolecular compounds, colloid chemistry, quantum chemistry, crystal chemistry, radiochemistry, etc.

The object of study of chemistry are substances – chemical forms of the existence of material objects. Every substance has certain physical and chemical properties.

Physical properties of a substance – state of aggregation, density, solubility, melting points, boiling points, color, taste, smell, viscosity, volatility, etc.

There are three states of aggregation of substances: solid, liquid and gaseous. Under normal conditions, various substances are in different states of aggregation. For example,

  • salt NaNO3, coal C, iron Fe – solids;
  • water H2O, acetic acid CH3COOH, octane C8H18 – liquid substances;
  • nitrogen N2, carbon dioxide CO2, ethane C2H6 – gaseous substances.

When conditions change (for example, temperature and pressure), any substance can change from one state of aggregation to another.

Physical phenomena are changes in the form or aggregate state of substances, as a result of which new substances are not formed.

The chemical property of a substance is the ability of a given substance to transform into other substances.

The transformation of one substance into another is called chemical reactions, or chemical phenomena. As a result of chemical reactions, new substances are always formed. The initial substances that enter into a chemical reaction are called reactants, and the new substances that are formed as a result of a chemical reaction are called reaction products.