The allotropy is an ability of chemical elements to be in a type of two and more simple substances. It is connected with various number of atoms in a molecule or with the structure of a crystal lattice.
Allotropy
There are more than 400 allotropic types of simple substances. However the exact reason explaining such modifications still is not revealed. In molecules of similar modifications, as a rule, different amount of atoms and the structure of crystal lattices owing to what physical properties of these substances differ. Allotropic modifications of arsenic, strontium, selenium, antimony are found, at high temperatures - iron and many other elements. The tendency to allotropy is more brightly shown at nonmetals. The exception is made by halogens and noble gases, and semi-metals.
Allotropic modifications
- Phosphorus. 11 allotropic modifications of phosphorus, including white, red and black are studied. All of them differ on physical properties. White phosphorus glows in the dark and can self-ignite while red does not ignite, does not possess a luminescence and is not poisonous. - Carbon. Long since an established fact that diamond and coal at combustion form carbon dioxide. From this it follows that the same element — carbon is their part. Carbon has many forms of binding of atoms among themselves therefore it is impossible to tell about number of its modifications precisely. Treat the most known - graphite, diamond, karbin, lonsdaleite, fullerenes carbon. - Sulfur. The similar difference characterizes molecules of two types of sulfur. The difference between molecules of sulfur is that atoms of octavalent sulfur form a vosmichlenny ring, and molecules hexavalent are built in linear chains of six atoms of sulfur. Under normal conditions all modifications of sulfur pass into rhombic. - Oxygen. Oxygen has two allotropic modifications: oxygen and ozone. Oxygen has no color and a smell. Ozone possesses a specific smell, pale violet color and is bactericidal substance. - Pine forest. At a pine forest more than 10 allotropic modifications. There is an amorphous pine forest in the form of brown powder and black crystal. Physical properties of these substances are various. So the reactionary ability of an amorphous pine forest is much higher, than crystal. - Silicon. Two core modifications of silicon are amorphous and crystal. There is a polycrystalline and single-crystal silicon. Their distinction consists in the structure of crystal lattices. - Antimony. Four metal and three amorphous allotropic modifications of antimony are studied: explosive, black and yellow. Metal modifications exist with a different pressure. From amorphous the steadiest form - silver-white color with a bluish shade.