From our article you will learn what allotropy is. This concept is widespread in nature. For example, oxygen and ozone are substances that consist only of the chemical element oxygen. How is this possible? Let's figure it out together.
Definition of concept
Allotropy is the phenomenon of the existence of one chemical element in the form of two or more simple substances. Jens Berzelius, a chemist and mineralogist from Sweden, is considered to be its discoverer. Allotropy is a phenomenon that has much in common with crystal polymorphism. This caused a long debate among scientists. At present, they have come to the conclusion that polymorphism is characteristic only for solid simple substances.
Causes of allotropy
Not all chemical elements can form several simple substances. The ability to allotropy is due to the structure of the atom. Most often, it occurs in elements that have a variable value of the oxidation state. These include semi- and non-metals, inert gases and halogens.
Allotropy can be due to several reasons. These include a different number of atoms, the order of their connection into a molecule, the parallelism of electron spins, the typecrystal lattice. Let's consider these types of allotropy using specific examples.
Oxygen and ozone
This type of allotropy is an example of how a different number of atoms of one chemical element determines the physical and chemical properties of a substance. This also applies to the physiological impact on living organisms. So, oxygen consists of two oxygen atoms, ozone - of three.
What is the difference between these substances? Both are gaseous. Oxygen has no color, taste or smell, it is one and a half times lighter than ozone. This substance is highly soluble in water, and with decreasing temperature, the rate of this process only increases. Oxygen is needed by all organisms for respiration. Therefore, this substance is vital.
Ozone is blue. Each of us felt its characteristic smell after the rain. It's harsh, but quite pleasant. Compared to oxygen, ozone is more reactive. What is the reason? When ozone decomposes, an oxygen molecule and a free oxygen atom are formed. It immediately enters into compound reactions, forming new substances.
The amazing properties of carbon
But the number of atoms in a carbon molecule always remains the same. At the same time, it forms completely different substances. The most common modifications of carbon are diamond and graphite. The first substance is considered the hardest on the planet. This property is due to the fact that the atoms in diamond are bound by strong covalent bonds in all directions. Together, they form a three-dimensional network of tetrahedra.
In graphite, strong bonds are formed only between atoms located in a horizontal plane. For this reason, it is almost impossible to break a graphite rod lengthwise. But the bonds that connect the horizontal layers of carbon to each other are very weak. Therefore, every time we draw a simple pencil on paper, a gray mark remains on it. This is the layer of carbon.
Allotropy of sulfur
The reason for the modification of sulfur also lies in the features of the internal structure of the molecules. The most stable shape is rhombic. Crystals of this type of sulfur allotropy are called rhomboidal. Each of them is formed by crown-shaped molecules, each of which includes 8 atoms. According to its physical properties, rhombic sulfur is a yellow solid. It not only does not dissolve in water, but is not even wetted by it. Heat and electrical conductivity are very low.
The structure of monoclinic sulfur is represented by a parallelepiped with oblique corners. Visually, this substance resembles dark yellow needles. If sulfur is melted and then placed in cold water, its new modification is formed. Its original structure will break down to polymer chains of different lengths. This is how plastic sulfur is obtained - a brown rubbery mass.
Phosphorus modifications
Scientists have 11 types of phosphorus. Its allotropy was discovered almost by accident, like this substance itself. In search of the philosopher's stone, the alchemist Brand received a luminousdry substance resulting from the evaporation of urine. It was white phosphorus. This substance is characterized by high chemical activity. It is enough to raise the temperature to 40 degrees for white phosphorus to react with oxygen and ignite.
For phosphorus, the cause of allotropy is a change in the structure of the crystal lattice. It can only be changed under certain conditions. So, by increasing the pressure and temperature in an atmosphere of carbon dioxide, red phosphorus is obtained. Chemically, it is less active, so it is not characterized by luminescence. When heated, it turns into steam. We see this every time we light regular matches. The grating surface just contains red phosphorus.
So, allotropy is the existence of one chemical element in the form of several simple substances. Most often found among non-metals. The main reasons for this phenomenon are considered to be a different number of atoms that form a molecule of a substance, as well as a change in the configuration of the crystal lattice.
