Metalloid

Under metalloids we usually consider the following chemical elements: boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb) and tellirium (Te). The rare and radioactive elements polonium (Po) and astatine (At) are sometimes included. They are placed in different groups of the periodic table: boron is in group 13, silicon and germanium in group 14, arsenic and antimony in group 15 and tellurium in group 16. The physical properties of metalloids are closer to metals. They are usually brittle, shiny solids that behave as electrical insulators at room temperature. They become more comparable to metals as electrical conductors when heated or when small quantities of certain elements are introduced into the lattices of their crystalline structures.

Boron is rare element. The estimated abundance in the Earth's crust 10mg/kg, thus, the estimated abundance in the ocean is 4.44mg/lit. The number of stable isotopes is 2. In nature boron is found in its minerals such as borax (Na2[B4O5(OH)4] x 8H2O. Silicon is the second most abundant elements in the Earth's crust 2.82x105mg/kg. It is important in the world of minerals as much as carbon in organic world. Silicon dioxide (SiO2), silicon's most common compound, is the most abundant compound in the Earth's crust. Furthermore, the Earth's crust is made mostly of different kinds of silicate. Two allotropes of silicon exist at room temperature: amorphous and cristallyne. There are 3 stable isotopes. Germanium is very rare element with abundance in the Earth's crust of 1.5mg/kg. It is found in nature in mineral argyrodite (Ag8GeS6) and in the ore named germanite. Germanium has 5 stable isotopes. Arsenic occurs free in nature, but is most often found in the minerals arsenopyrite (FeAs2 x FeS2), realgar (As4S4) and orpiment (As2S3). The estimated crustal abundance is 1.8mg/kg and it has 1 stable isotope. Arsenic occurs in two allotropes, yellow and grey. Antimony has been known from the ancient times. It is sometimes found free in nature, but is usually obtained from the ores stibnite (Sb2S3) and valentinite (Sb2O3). The estimated crustal abundance is 0.2mg/kg and it has 2 stable isotopes. Antimony occurs in three solid allotropes. Tellurium is also found free in nature but is most often found in the ores sylvanite (AgAuTe4) and calaverite (AuTe2). It is rare in nature, the estimated crustal abundance is 1x10-3mg/kg. The number of stable isotopes is 5. There are few allotropes of tellurium.      

Metalloids have electronic configurations in wide range from the nearly empty outer electron shells of the typical metals to the nearly filled electron shells of nonmetals. In that way have enough empty electron orbitals into which electrons can be moved to conduct electric current. They are solid, lustrous and brittle with electrical conductivity from intermediate to good. They are semiconductors or if not (arsenic and antimony are semimetallic) exist in semiconducting form. The ionization energies and electronegativity of metalloids are between nonmetals and metals, and as a result, metalloids have characteristics of both of these element categories. For example, although silicon has a characteristic metallic sheen, it is quite brittle and is an inefficient conductor. The element with which a metalloid reacts impacts the reactivity of metalloid. As an example, when boron reacts with fluorine it reacts like a metal, but when boron reacts with sodium it reacts like a nonmetal. The densities, boiling points and melting points of the metalloids vary widely. Because metalloids have an intermediate conductivity, they typically make good semiconductors.

As a summary, physical properties of metalloids are as follows:

• Metalloids have a solid state of matter.
• In general, metalloids have a metallic luster. Metalloids have low elasticity, they are very brittle.
• Middlewights are semi-conducted elements, and they allow leave the average transmission of heat.

Chemical properties of metalloids are as follows:

• Metalloids easily form gasses when they oxidize.
• Metalloids can be combined with metals to create alloys.
• Metalloids have different metallic and nonmetallic allotropes.
• When metalloids melt some of them will contract.
• Metalloids can react halogens to form compounds.
• Metalloids can form compounds with both positive and negative oxidation numbers.

Most of these elements are important industrial materials, being used to make transistors and other semiconductor devices, ceramics, solar batteries and certain polymers. The metalloids and their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage, optoelectronics, pyrotechnics, semiconductors and electronics.

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