What is allotropy? Allotropy of carbon, chemistry

The reasons for the diversity of organic compounds are the ability of carbon atoms to form various chains and cycles, connecting with each other. 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?

You can answer this question in this way. This phenomenon is the existence of the same chemical element in the form of several simple substances. That is, if the cells in the periodic table 118, then this does not mean that the nature of the atoms is the same. Each of the elements (almost all) have one or more varieties, or allotropic modifications.

What is the difference between such substances? The reasons for this phenomenon are the main two:

• Different number of atoms in the molecule (allotropy of the composition);
• Unequal structure of the crystal lattice (form allotropy).

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 different simple substances, regardless of the state of its aggregate state. While polymorphism is a concept applicable only to solid crystalline substances.

Various allotropic modifications of compounds are usually denoted by Latin letters before their name. Alpha is always placed before the form that has the minimum melting point, boiling point. Further on in alphabetical order and increase in indicators accordingly.

Despite the fact that the chemical element in the basis of simple substances is the same, the properties of the modifications differ significantly from one another, both physical and chemical. The most easily formed allotropic forms:

• Non-metals (except halogens and inert gases);
• Semimetals.

The allotropy of metals has been least studied, since they make such modifications unwillingly and not all. In total, more than 400 different forms of simple substances are known to date. The more degrees of oxidation is characteristic for an element, the higher the number of allotropic modifications known to it.

Modifications of carbon

Carbon allotropy is the most common and vivid example illustrating the phenomenon under consideration. After all, this element is able to form several types of compounds, differing in the structure of the crystal lattice. The resulting simple substances are so polar in their properties that it remains to be surprised at the solutions of nature.

So, allotropy of carbon includes the following modifications.

1. What is the allotropy of carbon can be traced in its next form, which is radically different from the previous one. This is graphite. Very soft substance, which can easily peel off and leave a characteristic trace on paper. Therefore, it is used for the manufacture of pencil leads. The structure of this form is hexagonal layered. The bonds between the interlayers are weak, easily torn, the density of matter is low. Used graphite for the production of synthetic diamonds, as a solid lubricant, for the manufacture of electrodes, as a filler of plastics, as well as in nuclear reactors.
2. Fullerenes are yet another proof that there is allotropy. The chemistry of these compounds is similar to that of aromatic hydrocarbons. After all, their structure is represented by convex closed polyhedra resembling a soccer ball. Fullerenes are used in engineering as a semiconductor, for the production of superconducting compounds, like photoresist and so on.
3. Lonsdaleite and cerafite are two more crystalline allotropic modifications of carbon. They were discovered relatively recently. By properties are very similar to diamond, in the absence of impurities can be even several times harder.
4. Coal and soot are amorphous allotropic substances. Used as fuel, lubricants, in filters and so on. By content in nature, the most common of all modifications of carbon.

Diamond

The most solid of all known substances for today, estimated at 10 points on the Mohs scale. The crystalline form of carbon, the structure of which has the appearance of properly connected tetrahedral formations to one another.

Diamond is able to disperse light very well, which makes it possible to use it as a 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;
• Nanopen;
• Astrologers;
• Nanofiber;
• Glassy carbon;
• Graphenes;
• Carbine;
• Nanopots.

Unconfirmed, but presumed forms of existence of simple carbon compounds: chaoite, metallic carbon and carbon dioxide.

Allotropy of oxygen

This non-metal forms two simple substances:

• Gas oxygen (under normal conditions), the formula of which is O ₂ ;
• Gaseous ozone, the empirical reflection of whose composition is O ₃ .

It is obvious that here the main reason for the existence of modifications is the composition of the molecule. Ordinary oxygen is the basis of the life of all living beings (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 oxidizer, through which many reactions are carried out.

Ozone is formed in nature or special laboratory installations of ozonizers from oxygen of air under the influence of a strong discharge of electricity. In natural conditions, 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 oxidizer, bleach, chemically active.

Modifications of phosphorus

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, and therefore the chemical bond and properties. There are three stable forms and the rest, in nature practically not occurring and decaying.

1. White phosphorus. His formula is P ₄ . A substance that resembles a soft paraffin of white or slightly yellowish color. Easily melts, passing into a poisonous gas.
2. Red phosphorus is a paste-like mass with an unpleasant odor. The formula is P _n . This is a polymer structure.
3. Black phosphorus is a greasy to the touch mass, which is black and completely insoluble in water.

Modifications of metals

What is the allotropy of metals, you can learn from the example of iron. It exists in the form:

• alpha-;
• beta-;
• gamma-;
• Sigma-form.

Each differs from the previous structure of the crystal lattice and, accordingly, properties. For example, the alpha-form is ferromagnetic, and the beta-paramagnet.

In general, of all known metals, allotropic modifications form only 27 chemical elements.

Allotrope of tin

Interestingly, the alpha-form is a gray powder that exists only at low temperatures. Beta-form, on the contrary, is metal, silvery-white, soft and plastic. It exists at high temperatures - up to 161 ^o C. One form easily passes into another under natural conditions, if there is a gradient difference.