Quasi metal

Terminology of Chemistry

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synonym Metalloid element (metalloid element) generally refers to quasi metal

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Metaloid, also known as Semimetal (semimetal), a substance between metals and nonmetals. Quasi metal is a kind of element, whose appearance shows the characteristics of metal, but its chemical properties show both metal and non-metallic properties. For example, arsenic and antimony are hard crystalline solids, apparently metallic in appearance, but they show two different properties when conducting chemical reactions: metallic and non-metallic. Some of their oxides are soluble in both acids and bases, which is the so-called amphoteric property, because their properties are like both bases and acids. Many elements can also be generated Amphoteric compound 。 However, only when the duality of this chemical property is very obvious and the appearance of metal is shown, can this element be called a quasi metal.

Chinese name: Quasi metal
Foreign name: metalloid
Alias: Semi metal 、 "Metal like", etc

Nature: be situated between Metal And Nonmetal between
Element: boron 、 silicon 、 arsenic 、 tellurium 、 antimony etc.
Purpose: Alloy additives, semiconductor materials, etc

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Basic Introduction

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Metaloid is also called "semi metal"“ Metalloid ”, "sub metal" or "metal like", with properties between metal and Nonmetal Elements between. These elements are generally brittle Metallic luster 。 Semi metal usually includes boron 、 silicon 、 arsenic 、 antimony 、 tellurium , heavy element Polonium and Astatine , although their physical chemical property Little is known, and it is generally included in semi metal, which is usually considered as metallic germanium and antimony , can also be classified as semi metal.^[1]

Semimetallic element stay periodic table of ele ments In the transition position from metal to nonmetal (see Nonferrous metal ）。 For example, a zigzag diagonal line is drawn along the periodic table between boron and aluminum in Group IIIA and between tellurium and polonium in Group VIA. It can be seen that the elements close to this diagonal line are semi metallic except aluminum. The elements on the right side of the semi metallic element belt are non-metallic, and those on the left side are metallic. The electronegativity of semi metallic elements is between 1.8 and 2.4, which is greater than that of metals and less than that of nonmetals. Their oxides and water Acting to form weak acid or Weak alkalinity Solution. They often act as electron donors when interacting with nonmetals, and as electron acceptors when interacting with metals.

Semi metals are mostly semiconductors with conductivity, resistivity Between metal (10 －5 Less than ohm · cm) and nonmetal (10 ten Ohm · cm). Conductivity The compliance with temperature is mostly opposite to that of metal; If half metal is heated, its conductivity increases with temperature. Semi metals have many different physical and chemical properties Allotrope ， tellurium 、 arsenic 、 silicon 、 boron The "amorphous" allotrope of selenium has more prominent non-metallic properties.^[1]

Quasi metal: arsenic

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1. Source and use

Arsenopyrite（ Arsenopyrite ）And Orthorhombic arsenite They are two kinds of ores that can be melted to produce simple arsenic. Arsenic and arsenic trioxide （As two O three ）It is produced as a commodity, and the latter is the raw material for the production of many arsenic compounds. The elemental arsenic is used to make alloys with lead and copper. Arsenic compounds have many uses, including as catalyzer 、 bactericide Rust remover, fungicide, animal feed additive antirust , drugs, veterinary drugs, tanning agents and Wood preservative 。 Arsenic is the first medicine to treat syphilis and has been used for treatment Amebic dysentery 。 Melamine, an organic arsenic compound, is the most effective drug for the treatment of neuropathy caused by African trypanosoma.

2. Exposure and absorption of arsenic

Arsenic can pass through the gastrointestinal system and lung The main concern of arsenic is internal absorption toxicity. Arsenic trichloride （AsCI three ）Lewis gas and organic arsenide (used as poison gas in World War I) can penetrate the skin, which are very harmful to the exposed person and are strong Erosive poison (causing blisters). Ordinary arsenide As two O three It is absorbed through the lungs and intestines. The size of solid particles is the main factor of how much it is absorbed. Coarse particle compounds tend to pass through the stomach and pass through the stool.

Arsenic has the+3 and+5 oxidation states, and the inorganic compounds in the+3 oxidation state are usually toxic. It is generally beneficial to the environment to convert to arsenic (V), and its harm is greatly reduced.

Arsenic is a natural component of most soils. Many foods contain arsenic, especially aquatic shellfish. Adults consume an average of less than 1 mg of arsenic per day from normal sources.

3. Metabolism, transfer and toxicity of arsenic

Arsenic (Ⅲ) interferes with ATP phosphorylation process

Biochemically, arsenic makes protein coagulation , forming complexes with coenzyme, inhibiting ATP（ Adenosine triphosphate ）Generation of. Similar to cadmium and mercury, arsenic is a "sulfur loving" element. Arsenic has some chemical characteristics similar to phosphorus, and replaces phosphorus in some chemical processes, playing an adverse role the new supersedes the old effect. This effect is summarized in the following figure "Process of arsenic (Ⅲ) interfering with ATP phosphorylation". The above reaction shows that 1,3-bis is synthesized from glyceraldehyde-3-phosphate by enzyme catalysis Glycerol phosphate Ester, its product continues to react to generate Adenosine triphosphate (ATP), which is an energy producing substance necessary for metabolism in human body. When arsenite AsO three 3- When it appears, it combines with glyceraldehyde-3-phosphate to form a product that can undergo non enzymatic spontaneous hydrolysis, preventing the formation of ATP.

Antidotes for arsenic poisoning can take advantage of its "sulfur affinity" and use substances containing sulfhydryl groups, such as 2,3 - Dimercaptopropanol （BAL）。^[2]

Quasi metallic luster

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One of the grades of semi metallic luster intensity. Generally, it refers to the reflectivity R=0.19~0.25, which is slightly darker than the fresh polished metal surface, just like the luster reflected by the surface of old metal utensils, such as the luster of magnetite. Semi metallic luster minerals are mostly opaque minerals, and are rarely used as gemstones.

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Quasi metals (semi metals) are mostly semiconductors resistivity Between metals and nonmetals. The characteristic of semi metal energy band is that there is a small part between its conduction band and its valence band overlap 。 unwanted Thermal excitation The electrons at the top of the valence band will flow into the bottom of the conduction band with lower energy. So in Absolute zero When the conduction band has a certain electron concentration, Price band There are also equal hole concentrations in. This is the fundamental difference between semi metals and semiconductors. However, due to the small overlap, it is also different from typical metals. Of this kind of material Band gap width It is very small, so it is used to make infrared detection devices. Infrared wavelength Is 10 micron Left and right, corresponding Photon energy Is 0.1 Electron volt 。 Semi metallic materials are exposed to infrared light to beam Later, electrons can be rapidly excited from the valence band to the conduction band, causing conductivity changes, thus detecting infrared light.

In addition to the above elements, compounds can also be semi metals, such as Mg two Pb。 Other compounds, such as HgTe and HgSe, have a band gap width equal to zero, sometimes called zero band gap semiconductors, which are also semi metals in essence.

The relationship between the conductivity of these elements and temperature is mostly opposite to that of metals, that is, their conductivity increases with temperature. Quasi metals are widely used in electrical and metallurgical fields, especially in semiconductor material Plays an important role in.^[3]

from Band structure It can be seen that the metal is filled with the highest number of electrons energy band It is half full or partially filled, and the electrons can move freely conductivity 。 insulator The highest energy band filled with electrons in Full belt (also known as Price band ）, between valence band and conduction band Band gap width Larger. At room temperature, electrons cannot be separated from valence band inspire reach conduction band The free moving electrons are generated, so the conductivity is very low. The energy band filled by electrons in semiconductors is similar to that of insulators, but the band gap is small. Under certain doping concentration, conductive free electron Or freedom hole 。 The conductivity of semiconductors is between metals and insulators. In addition, there is an intermediate case between metal and semiconductor, where the band gap width is zero or very small. At this time, electrons can be excited from the valence band to the conduction band at a very low temperature. There are electrons and holes that can move freely in both the conduction band and the valence band. Such as mercury telluride (HgTe), this material is called Semimetal 。

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