What is a substance? Structure and properties of substances
It is known from the physics course that atoms of chemical elements have the form of free particles. They can be combined with each other through various As a result, molecules of substances, both simple and complex, are formed. In this way, one of the forms of existence of matter, which is the most common on Earth, is formed. In our article we will consider the structure and properties of substances and give examples of their various states: solid, liquid and gaseous.
General characteristics of compounds
Oxygen, which breathes living beings, diamond placers, deposits of coal - these are examples of simple substances whose properties depend on the structure of their molecules. They contain atoms of only one chemical element - carbon, oxygen, nitrogen. Some of the elements can form not one, but several simple substances. They differ from each other not only in appearance, but also in their internal structure, and, therefore, in properties.We are talking about allotropic modifications, which we dwell on. Opposite to them are particles of a complex compound, which is another name for a substance, they consist of atoms of various elements. Water, salt, ethyl alcohol, starch - the list of complex compounds that make up the objects of the material world can be continued indefinitely.
The graphite core of a pencil, a diamond in a refined frame and a white crystalline powder of carbyan extracted from the Arizona crater ... are strikingly different ... But all three simple compounds named consist only of carbon atoms. Why are they so different from each other? What is a substance called allotropic modification in chemistry? We will find the answer in the internal structure of the compound, that is, in the features of the shape of its crystal lattice. In nature, allotropy occurs infrequently. Oxygen and ozone are another example of such substances. They differ in the number of oxygen atoms in the composition of the molecules: there are two of them in oxygen, and three in ozone.
Diamond and graphite
The giant molecule, in which each carbon atom is linked to four others at the same distance, is a diamond.Covalent bonds between particles are extremely durable, the crystal perfectly refracts the light rays, therefore it is considered the most expensive jewelry. It does not conduct electrical current and is a superhard natural material used for drilling wells and cutting glass. What is a substance - graphite? Its dark gray crystals are oily to the touch, soft and easily leave a mark on the paper. Atoms in the molecule are arranged in layers. It refers to the conductors of the current and is used in electrical engineering.
What is carbin?
Carbin is the third carbon modification. In the 60s of the 20th century, it was obtained in the laboratory of the Russian scientist V.V. Korshak, and then found in nature as part of a meteorite substance. The structure of its carbon chains is linear, the compound has the appearance of a fiber, powder or white films. Carbin has the properties of a semiconductor, ideally survives in the human body. Therefore, it is used for the production of artificial joint prostheses, blood vessels, elements in ophthalmology, urology and dental prosthetics.
State of matter
If a compound has an atomic structure and belongs to non-metals, then its particles are linked together by a single covalent bond. For this reason, such molecules are diatomic.What are the following formulas: Cl2N2,O2? These are molecules of chlorine, nitrogen, oxygen. In the above example, the substances are in a gaseous state and their particles move in different directions, and the interaction forces between them are very weak. A different picture is observed when the aggregate form of the compound is dense - condensed. Liquids and solids, unlike gases, at a constant temperature occupy a certain volume. Their particles attract each other strongly enough, the nature of such connections is electric. Interesting is the structure of metal compounds with a number of specific properties: thermal conductivity, ductility, ductility, and electrical conductivity. What is a substance-metal from the point of view of the structure of its crystal lattice? It can be compared with a giant complex of atoms containing common electrons. They move inside the crystal and form the so-called electron gas, which is the cause of all the above listed characteristics of metals. So, we have found that chemical compounds have three state of aggregation: solid, liquid and gaseous.
How does the internal structure of a substance determine its properties?
Solid crystalline form is most common in nature. The structure of a substance is determined by the configuration of its crystal lattice, which, in turn, affects the physical and chemical properties. For example, the highest hardness of a diamond is due to the fact that there are atoms in its lattice sites, the interaction forces between which are quite large. The covalent bonds that arose in this way firmly hold the particles near each other, ensuring the stability of the structure. Iodine crystals, in contrast, can quickly deteriorate when heated. Even without going into the liquid phase, iodine is sublimated to the formation of vapor, i.e., it sublimates. This phenomenon is explained by the peculiarities of the internal structure of crystalline iodine. In the nodes of his lattice at large distances from each other are molecules. Under the influence of high temperature, they easily detach from each other, forming a gas phase. Ion type lattice connections are excellent conductors of current. They are refractory and durable, have charged particles in the lattice sites - ions.Electrostatic attraction forces arise between cations and anions; therefore, salt crystals are sufficiently hard and durable.
Along with the well-known, trivial, that is, names that have long been established in everyday life, for example: baking soda or table salt, there is a rather diverse scientific classification of chemical compounds. So, in the rational nomenclature they are divided into simple and complex, metals and non-metals. In the IUPAC classifier, great attention is paid to various groups of organic compounds. The name of the substance in it depends on the presence in the molecule of single, double, triple bonds or cycles. For example, compounds containing a sigma bond are called alkanes, and molecules of unsaturated character are referred to as alkenes or alkynes. Due to the fact that the arsenal of new, synthetic organic compounds is constantly replenished, they are classified according to the IUPAC international nomenclature. This ensures the principle of systematicity and helps chemists from around the world conduct joint research.
In our article we answered the questions: what is a substance, and how its physical and chemical properties depend on its internal structure.