The main question that a person must know the answer to correctly understand the picture of the world is what is a substance in chemistry. This concept is formed back in school age and guides the child in further development. Starting to study chemistry, it is important to find points of contact with it at the household level, this allows you to clearly and readily explain certain processes, definitions, properties, etc.
Unfortunately, due to the imperfect education system, many people miss some fundamental basics. The concept of “substance in chemistry” is a kind of cornerstone; timely assimilation of this definition gives a person the right start in the subsequent development in the field of natural science.
Concept formation
Before moving on to the concept of matter, it is necessary to determine what the subject of chemistry is. Substances - this is what directly studies chemistry, their mutual transformations, structure and properties. In a general sense, a substance is what physical bodies are made of.
So what is a substance in chemistry? We formulate the 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 type of matter - a field that does not have mass (electric, magnetic, biofield, etc.). Matter, in turn, is what we are made of and everything that surrounds us.
A slightly different characteristic of matter, determining what it specifically consists of, is already a subject of chemistry. Substances are formed by atoms and molecules (some by ions), which means that any substance consisting of these formula units is a substance.
Simple and complex substances
After mastering the basic definition, we can proceed to complicate it. Substances are of various levels of organization, that is, simple and complex (or compounds) - this is the very first division into classes of substances, chemistry has many subsequent divisions, detailed and more complex. This classification, unlike many others, has strictly defined boundaries; each compound can be clearly attributed to one of the species mutually exclusive of each other.
A simple substance in chemistry is a compound consisting of atoms of only one element from the periodic table. As a rule, these are binary molecules, that is, consisting of two particles connected by means of a covalent non-polar bond - the formation of a common unshared electron pair. So, the atoms of the same chemical element have identical electronegativity, that is, the ability to hold the total electron density, therefore it is not biased towards any of the bond participants. Examples of simple substances (non-metals) are hydrogen and oxygen, chlorine, iodine, fluorine, nitrogen, sulfur, etc. A molecule of a substance such as ozone consists of three atoms, and one of all noble gases (argon, xenon, helium, etc.). In metals (magnesium, calcium, copper, etc.) there is its own type of bond - metal, which is realized due to the socialization of free electrons inside the metal, and the formation of molecules as such is not observed. When recording a metal substance, just a symbol of a chemical element is indicated without any indexes.
A simple substance in chemistry, examples of which were given above, differs from a complex in 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 different electronegativity, when a common electron pair is formed, it shifts toward a more electronegative element, which leads to a general polarization of the molecule. The ionic type is the extreme case of the polar one, when a pair of electrons completely transfers to one of the binding participants, then atoms (or their groups) turn into ions. There is no clear border between these types, the ionic bond can be interpreted as covalent strongly polar. Examples of complex substances are water, sand, glass, salts, oxides, etc.
Substance modifications
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. The basis is still one element, but the quantitative composition, structure, and properties fundamentally distinguish such formations. This feature is called allotropy.
Oxygen, sulfur, carbon and other elements have several allotropic modifications. For oxygen, this is O 2 and O 3 , carbon gives four types of substances - carbine, diamond, graphite and fullerenes, the sulfur molecule can be rhombic, monoclinic, and plastic. 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 they are powerful antioxidants.
What happens to substances?
Every second in and around the transformation of substances. Chemistry considers and explains those processes that go with a qualitative and / or quantitative change in the composition of reacting molecules. In parallel, physical transformations often proceed in an interconnected manner, which are characterized only by a change in the shape, color of substances or state of aggregation and some other characteristics.
Chemical phenomena are reactions of various kinds, for example, compounds, substitution, exchange, decomposition, 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 of ozone under it is a chemical process.
Physical properties
A substance in chemistry is matter that has certain physical properties. By their presence, absence, degree and intensity, it is possible to predict how a substance will behave under certain conditions, and also explain some chemical characteristics of the compounds. For example, the high boiling points of organic compounds in which there is hydrogen and an electronegative heteroatom (nitrogen, oxygen, etc.) indicate that such a chemical type of interaction as a hydrogen bond appears in a substance. Thanks to the knowledge about which substances have the best ability to conduct electric current, cables and wires are made of certain metals.
Chemical properties
The establishment, research, and study of the other side of the property coin is done by chemistry. The properties of substances from her point of view are their reactivity to interaction. Some substances are extremely active in this sense, for example, metals or any oxidizing agents, while others, noble (inert) gases, under normal conditions practically do not enter into the reaction. Chemical properties can be activated or passivated if necessary, sometimes this is not associated with special difficulties, and in some cases it is not easy. Scientists spend many hours in laboratories, using trial and error to achieve their goals, sometimes they do not reach them. By changing environmental parameters (temperature, pressure, etc.) or by using special compounds - catalysts or inhibitors - you can affect the chemical properties of substances, and therefore the course of the reaction.
Chemical classification
All classifications are based on the separation of compounds into organic and inorganic. The main element of organics is carbon, combining with each other and hydrogen, carbon atoms form a hydrocarbon skeleton, which is then filled with other atoms (oxygen, nitrogen, phosphorus, sulfur, halogens, metals and others), closes in cycles or branches, thereby substantiating a wide variety of organic compounds. Today, science knows 20 million of these substances. While mineral compounds are only half a million.
Each compound is individual, but has many similar features with others in properties, structure and composition; on this basis, a grouping into classes of substances occurs. Chemistry has a high level of systematization and organization, it is an exact science.
Inorganic substances
1. Oxides - binary compounds with oxygen:
a) acidic - when reacted with water, they give acid;
b) basic - when interacting with water, they give a basis.
2. Acids - substances consisting of one or more protons of hydrogen and an acid residue.
3. Bases (alkalis) - consist of one or more hydroxyl groups and a metal atom:
a) amphoteric hydroxides - exhibit the 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 contains a proton, the result of incomplete dissociation of the acid;
b) basic salts - a hydroxyl group is associated with the metal, the result of incomplete dissociation of the base.
Organic compounds
There are a great many classes of substances in organic matter, such a volume of information is difficult to remember immediately. The main thing is to know the main divisions into aliphatic and cyclic compounds, carbocyclic and heterocyclic, limit and unsaturated. Hydrocarbons also have many derivatives in which the hydrogen atom is replaced by halogen, oxygen, nitrogen and other atoms, as well as functional groups.
A substance in chemistry is the basis of existence. Thanks to organic synthesis, people today have a huge number of artificial substances that replace natural ones, and also have no analogues in nature in nature.