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 at school age and guides the child in further development. When starting to study chemistry, it is important to find common ground with it at the everyday level, this allows you to clearly and easily explain certain processes, definitions, properties, etc.
Unfortunately, due to the imperfection of the education system, many people miss some fundamental basics. The concept of "substance in chemistry" is a kind of cornerstone, the timely assimilation of this definition gives a person the right start in the subsequent development in the field of natural science.
Formation of concept
Before moving on to the concept of matter, it is necessary to define what the subject of chemistry is. Substances are what chemistry directly studies, their mutual transformations, structure and properties. In a general sense, matter is what physical bodies are made of.
So, what is a substance in chemistry? Let us form a definition by passing from a general concept to a purely chemical one. Substance is a certain type of matter, necessarily having a mass, whichcan be measured. This characteristic distinguishes matter from another type of matter - a field that has no mass (electric, magnetic, biofield, etc.). Matter, in turn, is what we and everything around us are made of.
A slightly different characteristic of matter, which determines what it is made of - this is already a subject of chemistry. Substances are formed by atoms and molecules (some ions), which means that any substance consisting of these formula units is a substance.
Simple and complex substances
After mastering the basic definition, you can move on to complicating it. Substances come in different 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 connection can be clearly attributed to one of the mutually exclusive species.
A simple substance in chemistry is a compound consisting of atoms of only one element from the periodic table of Mendeleev. As a rule, these are binary molecules, that is, consisting of two particles connected through a covalent non-polar bond - the formation of a common lone electron pair. So, atoms of the same chemical element have identical electronegativity, that is, the ability to hold a common electron density, so it is not shifted to any of the bond participants. Examples of simple substances (non-metals) -hydrogen and oxygen, chlorine, iodine, fluorine, nitrogen, sulfur, etc. A molecule of such a substance as ozone consists of three atoms, and all noble gases (argon, xenon, helium, etc.) consist of one. In metals (magnesium, calcium, copper, etc.) there is its own type of bond - metallic, which is carried out 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, simply the symbol of the chemical element is indicated without any indices.
A simple substance in chemistry, examples of which were given above, differs from a complex one in its qualitative composition. Chemical compounds are formed by atoms of different elements, from two or more. In such substances, covalent polar or ionic type of binding takes place. Since different atoms have different electronegativity, when a common electron pair is formed, it shifts towards a more electronegative element, which leads to a common polarization of the molecule. The ionic type is an extreme case of the polar one, when a pair of electrons completely passes to one of the binding participants, then the atoms (or groups of them) turn into ions. There is no clear boundary between these types, the ionic bond can be interpreted as a covalent strongly polar. Examples of complex substances are water, sand, glass, s alts, oxides, etc.
Substance Modifications
Substances that are called simple actually have a unique feature that is not inherent in complex ones. Some chemical elements can form several formssimple substance. The basis is still one element, but the quantitative composition, structure and properties radically distinguish such formations. This feature is called allotropy.
Oxygen, sulfur, carbon and other elements have several allotropic modifications. For oxygen, these are O2 and O3, carbon gives four types of substances - carbine, 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 those listed 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 inside and around there is a transformation of substances. Chemistry considers and explains those processes that go with a qualitative and / or quantitative change in the composition of the reacting molecules. In parallel, often interconnected, physical transformations also occur, which are characterized only by a change in the shape, color of substances or the state of aggregation and some other characteristics.
Chemical phenomena are interaction reactions 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 conductivityetc. Often they accompany each other, for example, lightning during a thunderstorm is a physical process, and the release of ozone under its action is a chemical one.
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 a substance will behave in certain conditions, as well as explain some chemical features of compounds. So, for example, high boiling points of organic compounds that contain hydrogen and an electronegative heteroatom (nitrogen, oxygen, etc.) indicate that such a chemical type of interaction as a hydrogen bond is manifested in a substance. Thanks to the knowledge of which substances have the best ability to conduct electric current, cables and wires of electrical wiring are made from certain metals.
Chemical properties
Establishment, research and study of the other side of the coin of properties is 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, practically do not enter into reactions under normal conditions. Chemical properties can be activated or passivated as needed, sometimes without much difficulty, and in some cases not easily. Scientists spend many hours in laboratories, through trial and error, achieving their goals.goals, sometimes they are not achieved. By changing the environmental parameters (temperature, pressure, etc.) or using special compounds - catalysts or inhibitors - it is possible to influence the chemical properties of substances, and hence the course of the reaction.
Classification of chemicals
All classifications are based on the division 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 justifying a wide variety of organic compounds. To date, 20 million such substances are known to science. While there are only half a million mineral compounds.
Each compound is individual, but it also has many similar features with others in properties, structure and composition, on this basis there is a grouping into classes of substances. Chemistry has a high level of systematization and organization, it is an exact science.
Inorganic substances
1. Oxides are binary compounds with oxygen:
a) acidic - when interacting with water, they give acid;
b) basic - when interacting with water, they give a base.
2. Acids are 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. S alts are the result of a neutralization reaction between an acid and an alkali (a soluble base), consisting of a metal atom and one or more acid residues:
a) acidic s alts - the anion of the acid residue contains a proton, the result of incomplete dissociation of the acid;
b) basic s alts - a hydroxyl group is bound to the metal, the result of incomplete dissociation of the base.
Organic Compounds
There are a great many classes of substances in organic matter, it is difficult to remember such a volume of information at once. The main thing is to know the basic divisions into aliphatic and cyclic compounds, carbocyclic and heterocyclic, saturated 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.
Substance in chemistry is the basis of existence. Thanks to organic synthesis, a person today has a huge amount of artificial substances that replace natural ones, and also have no analogues in their characteristics in nature.
