| 13 | 14 | 15 | sixteen | 17 | |
|---|---|---|---|---|---|
| 2 | B Boron | C Carbon | N Nitrogen | O Oxygen | F Fluorine |
| 3 | Al Aluminum | Si Silicon | P Phosphorus | S Sulfur | Cl Chlorine |
| four | Ga Gallium | Ge Germanium | As Arsenic | Se Selenium | Br Bromine |
| five | In Indium | Sn Tin | Sb Antimony | Te Tellurium | I Iodine |
| 6 | Tl Thallium | Pb Lead | Bi Bismuth | Po Polonium | At Astatine |
Semimetals ( metalloids ) are chemical elements located in the periodic system at the interface between metals and non-metals . They are characterized by the presence of a covalent crystal lattice and metallic conductivity .
In solid state physics, semimetals are various substances that occupy an intermediate position between metals and semiconductors in electrical properties.
Semimetals include silicon , boron , germanium , arsenic , antimony , tellurium , sometimes bismuth , polonium [1] [2] and astatine , as well as tin , which has a semiconductor shape, and allotropic modifications of carbon - graphite and phosphorus - metallic phosphorus . Tennessin is also probably a semimetal [3] .
By their chemical properties, the elements boron, silicon, arsenic and tellurium are non-metals, but germanium and antimony, along with non-metallic properties, also have metallic properties (for example, they react with acids to form salts). By type of conductivity, boron, silicon, germanium, and tellurium are semiconductors, while arsenic and antimony have metallic conductivity. The melts of germanium and silicon also have metallic conductivity. According to their external characteristics, germanium, antimony and tellurium have pronounced signs of metals (characteristic luster, color); they are much weaker in boron, silicon and arsenic. All simple substances of these elements are characterized by a crystalline structure, high hardness and fragility.
Unlike semiconductors, semimetals have electrical conductivity near absolute zero temperature , while semiconductors (especially dielectrics) under these conditions are insulators [4] .
A characteristic feature of semimetals is the weak overlap of the valence and conduction bands, which leads, on the one hand, to the fact that semimetals remain conductors of electric current up to absolute zero temperature, and on the other hand, with increasing temperature, the number of current carriers ( electrons and holes ) increases, but nevertheless remains small, reaching a concentration of 10 18 –10 20 cm −3 , or 10 −3 per atom.
Current carriers in semimetals are characterized by high mobility and low effective mass . Due to this, semimetals are the most suitable objects for observing dimensional effects, phase transitions of a semimetal - dielectric in strong magnetic fields, and a number of other phenomena.
Types of semimetals
Semimetals are of various types: elements that are closer in properties to metals (germanium, antimony, polonium), elements that are average in properties, that is, having metallic external features, and in chemical reactions are closer to non-metals (boron, silicon, arsenic, tellurium ), elements that are almost entirely metals, but exhibiting slightly noticeable non-metallic features (beryllium, aluminum, bismuth, tin, gallium, zinc) and elements that exhibit non-metallic properties, but with some allotropic modifications similar to metals (hydrogen (non-metal is completely in all respects, but behaves like a metal in chemical reactions), carbon (mod. graphite), phosphorus (mod. black phosphorus), selenium (mod. gray selenium) and iodine). It turns out that only nitrogen, oxygen, fluorine, sulfur, chlorine, bromine and all inert gases belong to the “non-metals” class.
Notes
- ↑ Semimetals - article from the Chemical Encyclopedia
- ↑ Semimetals in the Great Soviet Encyclopedia
- ↑ D. Bonchev, V. Kamenska. Predicting the Properties of the 113–120 Transactinide Elements (English) // Journal of Physical Chemistry : journal. - American Chemical Society, 1981. - Vol. 85 , no. 9 . - P. 1177-1186 . - DOI : 10.1021 / j150609a021 .
- ↑ XuMuK.ru - SEMI-METALS - Chemical Encyclopedia . www.xumuk.ru. Date of treatment January 23, 2017.