A substance in chemistry is what? Properties of substances. Classes of substances

The main question that a person must know the answer to correctly understand the picture of the world is what is matter in chemistry. This concept is formed even at school age and directs the child in further development. When it comes to studying chemistry, it is important to find common ground with it at a household level, this allows us to clearly and easily explain certain processes, definitions, properties, etc.

Unfortunately, due to the imperfection of the education system, many are missing some fundamental elements. The concept of "substance in chemistry" is a kind of cornerstone, the timely assimilation of this definition gives a person a right start in the subsequent development in the field of natural science.

Formation of the concept

Before moving on to the concept of matter, it is necessary to determine what is the subject of chemistry. Substances - this is what directly studies chemistry, their mutual transformations, structure and properties. In general, substance is what physical bodies are made of.

So, what is a substance in chemistry? Form a definition by moving from a general concept to a purely chemical one. A substance is a certain type of matter, necessarily having a mass that can be measured. This characteristic distinguishes a substance from another kind of matter - a field that has no mass (electric, magnetic, biofield, etc.). Matter, in turn, is what we are made of and everything that surrounds us.

A somewhat different characteristic of matter, which determines what exactly it consists of is already a subject of chemistry. Substances are formed by atoms and molecules (some ions), and therefore any substance consisting of these formula units is matter.

Simple and complex substances

After mastering the basic definition, you can proceed to its complication. Substances come in different levels of organization, that is, simple and complex (or compounds) - this is the very first division into substance classes, chemistry has many subsequent divisions, detailed and more complex. This classification, unlike many others, has strictly defined boundaries, each connection can be clearly attributed to one of the types that are mutually exclusive.

A simple substance in chemistry is a compound consisting of atoms of only one element from the periodic table of Mendeleyev. As a rule, these are binary molecules, that is, consisting of two particles connected by means of a covalent nonpolar bond-the formation of a total unpaired electron pair. Thus, atoms of the same chemical element have identical electronegativity, that is, the ability to keep the total electron density, so it is not biased to any of the participants in the connection. Examples of simple substances (nonmetals) are hydrogen and oxygen, chlorine, iodine, fluorine, nitrogen, sulfur, etc. Of the three atoms is a molecule of such a substance as ozone, and from one - all noble gases (argon, xenon, helium, etc.). In metals (magnesium, calcium, copper, etc.), there is its own type of bond - metal, which is due to the socialization of free electrons inside the metal, and the formation of molecules as such is not observed. When writing a metal substance, simply a symbol of a chemical element is indicated without any indices.

A simple substance in chemistry, the examples of which were given above, differ from the complex by the qualitative composition. Chemical compounds are formed by atoms of different elements, from two or more. In such substances, there is a covalent polar or ionic type of binding. Since different atoms have a different electronegativity, then when a common electronic pair forms, it shifts toward a more electronegative element, which leads to a general polarization of the molecule. The ion type is the extreme case of the polar one, when a pair of electrons completely passes to one of the binding participants, then the atoms (or their groups) are converted into ions. There is no clear boundary between these types, the ionic bond can be interpreted as covalent strongly polar. Examples of complex substances - water, sand, glass, salts, oxides, etc.

Modifications of substances

Substances called simple, in fact have a unique feature that is not inherent in complex. Some chemical elements can form several forms of a simple substance. At the heart of everything is just one element, but the quantitative composition, structure and properties are radically different from such formations. This feature is called allotropy.

Oxygen, sulfur, carbon and other elements have several allotropic modifications. For oxygen - it is O ₂ and O ₃ , carbon gives four types of substances - carbyne, diamond, graphite and fullerenes, the sulfur molecule is rhombic, monoclinic and plastic modification. Such a simple substance in chemistry, examples of which are not limited to the above, is of great importance. In particular, fullerenes are used as semiconductors in technology, photoresistors, additives for the growth of diamond films and for other purposes, and in medicine these are the most powerful antioxidants.

What happens to the substances?

Every second inside and around, there is a transformation of substances. Chemistry considers and explains those processes that come with a qualitative and / or quantitative change in the composition of the reacting molecules. In parallel, physical transformations often occur interconnected, which are characterized only by changes in form, color of matter or aggregate state and some other characteristics.

Chemical phenomena are reactions of interaction of various kinds, for example, compounds, substitutions, exchanges, decompositions, reversible, exothermic, redox, etc., depending on the change in the parameter of interest. Physical phenomena include: evaporation, condensation, sublimation, dissolution, freezing, electrical conductivity, etc. Often, they accompany each other, for example, lightning during a thunderstorm is a physical process, and the release under its action of ozone is chemical.

Physical properties

A substance in chemistry is a matter that has certain physical properties. By their presence, absence, degree and intensity, one can predict how the substance behaves under certain conditions, and also explain some of the chemical characteristics of the compounds. Thus, for example, the high boiling points of organic compounds in which there is hydrogen and an electronegative heteroatom (nitrogen, oxygen, etc.) indicate that the substance exhibits a chemical type of interaction, such as a hydrogen bond. Due to the knowledge of what substances have the best ability to conduct electric current, the cables and wires of the electrical wiring are made from certain metals.

Chemical properties

The establishment, research and study of the other side of the medal of properties is concerned with chemistry. The properties of substances from its point of view are their reactivity to interaction. Some substances are extremely active in this sense, for example, metals or any oxidants, and other noble (inert) gases, under normal conditions, practically do not enter into the reaction. Chemical properties can be activated or passivated if necessary, sometimes it does not involve special difficulties, and in some cases it is not easy. Scientists spend many hours in laboratories, by trial and error trying to achieve their goals, sometimes they do not reach them. Changing the parameters of the environment (temperature, pressure, etc.) or using special compounds - catalysts or inhibitors - can affect the chemical properties of substances, and hence the course of the reaction.

Classification of chemicals

All classifications are based on the separation of compounds into organic and inorganic compounds. The main element of organic matter is carbon, connecting with each other and hydrogen, the carbon atoms form a hydrocarbon skeleton, which is then filled up with other atoms (oxygen, nitrogen, phosphorus, sulfur, halogens, metals, etc.), closes in cycles or branches, thereby justifying A wide variety of organic compounds. To date, science knows 20 million of these substances. While mineral compounds are only half a million.

Each compound is individual, but it has many similarities with others in properties, structure and composition, on this basis grouping into classes of substances takes place. Chemistry has a high level of systematization and organization, this is an exact science.

Inorganic substances

1. Oxides - binary compounds with oxygen:

A) Acidic - in the interaction with water give an acid;

B) basic - when interacting with water give a basis.

2. Acids - substances consisting of one or more hydrogen protons and an acid residue.

3. Bases (alkalis) - consist of one or more hydroxyl groups and a metal atom:

A) amphoteric hydroxides - exhibit properties of both acids and bases.

4. Salts - the result of the neutralization reaction between acid and alkali (soluble base), consist of a metal atom and one or more acid residues:

A) acid salts - the anion of the acid residue has a proton in the composition, the result of incomplete dissociation of the acid;

B) basic salts - a hydroxyl group is bonded to the metal, the result of incomplete dissociation of the base.

Organic compounds

Classes of substances in organics are great, this amount of information is difficult to remember right away. The main thing is to know the main divisions into aliphatic and cyclic compounds, carbocyclic and heterocyclic, limiting and unsaturated. Also hydrocarbons have many derivatives in which the hydrogen atom is replaced by halogen, oxygen, nitrogen and other atoms, as well as functional groups.

Substance in chemistry is the basis of existence. Thanks to organic synthesis, man today has a huge number of artificial substances that replace natural, and also have no analogues in their characteristics in nature.