The reasons for the variety of organic compounds are the ability of carbon atoms to form various chains and cycles, connecting together. That is the phenomenon of isomerism. And what is the reason for the variety of simple inorganic substances? It turns out that this question can be answered by considering what allotropy is. It is with this natural phenomenon in the world of chemical elements that the existence of various forms of simple compounds is associated.
What is allotropy?
The answer to this question is as follows. This is the phenomenon of the existence of the same chemical element in the form of several simple substances. That is, if there are 118 cells in the periodic table, this does not mean that there are as many atoms in the nature. Each of the elements (almost all) have one or more varieties, or allotropic modifications.
What is the difference between such substances? There are two main reasons for this phenomenon:
- different number of atoms in the molecule (allotropy of the composition);
- unequal structure of the crystal lattice (allotropy of the form).
Often this concept is associated with the term polymorphism. However, there is a difference between them. What is allotropy? This is a modification of a chemical element into various simple substances, regardless of the state of aggregation. While polymorphism is a concept applicable only to solid crystalline substances.
Various allotropic modifications of the compounds are usually denoted by Latin letters before their name. Alpha is always put before that form, which has a minimum melting point, boiling point. Further alphabetically and increase indicators respectively.
Despite the fact that the chemical element in the basis of simple substances is the same, the properties of the modifications differ significantly from each other, both physical and chemical. Allotropic forms are most easily formed:
- non-metals (except for halogens and inert gases);
- semimetals.
The least studied allotropy of metals, since they form such modifications are reluctant and not all. In total, more than 400 different forms of simple substances are known to date. The more oxidation states characteristic of an element, the higher the number of allotropic modifications known to it.
Carbon modifications
Carbon allotropy is the most common and vivid example illustrating this phenomenon. Indeed, it is this element that is capable of forming several types of compounds that differ in the structure of the crystal lattice. Moreover, the formed simple substances are so polar in their properties that one can only be surprised at the decisions of nature.
So, allotropy of carbon includes the following modifications.
- What is carbon allotropy can also be traced to its next form, which is radically different from the previous one. This is graphite. A very soft substance that can easily peel off and leave a characteristic mark on paper. Therefore, it is used for the manufacture of lead pencils. The structure of this form is hexagonal layered. The bonds between the layers are weak, easily torn, the density of the substance is low. Graphite is used to produce synthetic diamonds, as a solid lubricant, for the manufacture of electrodes, as a filler in plastics, and also in nuclear reactors.
- Fullerenes are further evidence that allotropy exists. The chemistry of these compounds is similar to that of aromatic hydrocarbons. After all, their structure is represented by convex closed polyhedrons resembling a soccer ball. Fullerenes are used in technology as a semiconductor, for the production of superconducting compounds, such as photoresist and so on.
- Lonsdaleite and cerafite are two more crystalline allotropic modifications of carbon. They were opened relatively recently. The properties are very similar to diamond, in the absence of impurities they can even be several times harder.
- Coal and soot - amorphous allotropy of substances. Used as fuel, lubricants, filters and so on. By the content in nature, the most common of all carbon modifications.
Diamond
The hardest of all known substances today, estimated at 10 points on the Mohs scale. The crystalline form of carbon, the structure of which looks like tetrahedral formations correctly connected to each other in a network.
A diamond is able to scatter light very well, which allows it to be used as jewelry (diamonds). Due to its extreme hardness, it is used for cutting and welding, drilling, polishing and grinding. To date, production of artificial diamonds used in industry has been established.
Other varieties
There are also several varieties of this element:
- nanotubes;
- nanofoams;
- astrolenes;
- nanofibres;
- glassy carbon;
- graphene;
- carbine;
- nanopods.
Unconfirmed, but assumed forms of the existence of simple carbon compounds: chaoite, metallic carbon, and diocarbon.
Oxygen allotropy
This non-metal forms two simple substances:
- oxygen gas (under ordinary conditions), the formula of which is O 2 ;
- gaseous ozone, an empirical reflection of the composition of which is O 3 .
Obviously, here the main reason for the existence of modifications is the composition of the molecule. Ordinary oxygen is the basis of life for all living things (with the exception of anaerobic bacteria). He is an active participant in gas exchange, a source of energy for all life processes. Chemically, it is an oxidizing agent, through which many reactions are carried out.
Ozone is formed in nature or in special laboratory facilities ozonizers from oxygen in the air under the influence of a strong discharge of electricity. In vivo - this is lightning. In low dispersed concentrations it has a pleasant smell of freshness (after a thunderstorm it is always felt in the air). It is a very strong oxidizing agent, bleach, chemically active.
Phosphorus Modifications
Allotropy of oxygen is similar to that of phosphorus. It also has about 11 different modifications, differing in the number of atoms in the molecule, which means chemical bonding and properties. Three stable forms are distinguished and the rest, which are practically not found and decaying in nature.
- White phosphorus Its formula is P 4 . A substance resembling soft paraffin of white or slightly yellowish color. It melts easily, turning into toxic gas.
- Red phosphorus is a pasty mass with an unpleasant odor. Formula - P n . This is a polymer structure.
- Black phosphorus is a greasy to the touch mass that is black in color and completely insoluble in water.
Modifications of metals
What is metal allotropy can be found on the example of iron. It exists in the form:
- alpha-;
- beta-;
- gamma-;
- sigma forms.
Each differs from the previous structure of the crystal lattice and, accordingly, properties. For example, the alpha form is ferromagnet, and the beta paramagnet.
In general, of all known metals, allotropic modifications form only 27 chemical elements.
Tin Allotropy
Interestingly, the alpha form is a gray powder that exists only at low temperatures. The beta form, on the contrary, is metal, silver white, soft and ductile. It exists at high temperatures - up to 161 ° C. One form easily passes into another in vivo if there is a degree difference.