Allotropy is the ability of atoms of one element to form different types of simple substances. Thus, compounds are formed that are different from each other.
Allotropic modifications are stable. Under constant pressure at a certain temperature, these substances can pass one into the other.
Allotropic modifications can be formed from molecules having a different number of atoms. For example, the oxygen element forms ozone (O3) and the substance oxygen itself (O2).
Allotropic modifications can be solids having different crystal structures. Such compounds include, for example, diamond and graphite. These substances are allotropic modifications of carbon. This chemical element can form five simple substances: hexagonal and cubic diamond, graphite, carbin (in two forms).
Hexagonal diamond was found in meteorites and obtained in laboratory conditions with prolonged heating under the influence of very high pressure.
Diamond, as you know, is the hardest of all substances that exist in nature. It is used in rock drilling and glass cutting. Diamond is a colorless transparent crystalline substance that has high light refraction. Diamond crystals have a cubic face-centered lattice. Half of the crystal atoms are located at the centers of the faces and vertices of one cube, and the remaining half of the atoms are located at the centers of the faces and vertices of another cube, which is offset relative to the first along the spatial diagonal. Atoms form a tetrahedral three-dimensional network in which they have covalent bonds.
Of all simple substances, only in diamond is there a maximum number of atoms that are very densely arranged. Therefore, the connection is very strong and solid. Strong bonds in carbon tetrahedra provide high chemical resistance. Only fluorine or oxygen can affect a diamond at a temperature of eight hundred degrees.
Without air access, with strong heating, the diamond turns into graphite. This substance is represented by dark gray crystals . Graphite has a faint metallic luster. The substance is oily to the touch. Graphite is resistant to heat, has a relatively high thermal and electrical conductivity. The substance is used in the manufacture of pencils.
Carbin is obtained synthetically. It is a black solid with a glass sheen. Without air access, when heated, the carbin turns into graphite.
There is another form of carbon - amorphous carbon. This disordered structure is obtained by heating carbon-containing compounds. Large deposits of coal are found in natural conditions. In this case, the substance has several varieties. Coal can be presented in the form of soot, bone coal or coke.
As already indicated, allotropic modifications of one element are characterized by different interatomic structures. In addition, they are endowed with various chemical and physical properties.
Sulfur is another element capable of allotropy. This substance has been used by humans since ancient times. There are different allotropic modifications of sulfur. The most popular is rhombic. It is represented by a yellow solid. Rhombic sulfur is not wetted by water (floats on the surface). This property applies to the extraction of a substance. Rhombic sulfur is soluble in organic solvents. The substance has poor electrical and thermal conductivity.
In addition, there is plastic and monoclinic sulfur. The first is a brown amorphous (rubber-like) mass. It is formed when molten sulfur is poured into cold water. Monoclinic is presented in the form of dark yellow needles. Under the influence of room temperature (or close to it), both of these modifications transform into rhombic sulfur.