Nonmetals boron

Semimetals Seven of the nine elements adjacent to the zigzag boundary between metals and nonmetals—boron, silicon, germanium, arsenic, antimony, tellurium, and astatine—are known as semimetals, or metalloids, because their properties are intermediate between those of their metallic and nonmetallic neighbors. Though most are silvery in appearance and all are solid at room temperature, semimetals are brittle rather than malleable and tend to be poor conductors of heat and electricity. Silicon, for example, is a widely used semiconductor, a substance whose electrical conductivity is intermediate between that of a metal and an insulator. 

Nonmetals. Boron, activated carbon, silicon, and phosphorus ignite in gaseous chlorine.14,21,28... 

Nonmetals. Boron or yellow phosphorus explodes violently on grinding with the oxide and sulfur or red phosphorus ignites on grinding with the oxide.19... 

Nonmetals. Boron reacts violently with concentrated HN03. Phosphorus vapor may ignite. Silicon, arsenic, and finely divided carbon react violently.40... 

Stokinger HE. 1981. The halogens and the nonmetals boron and silicon. In Clayton GD, Clayton FE, eds. Patty s industrial hygiene and toxicology. 3rd ed. Vol. 2B. New York, NY John Wiley and Sons, 3021-3023. 

Elements in this group include one nonmetal, boron, and four elements that are primarily metallic in their properties. Physical properties of these elements are shown in Table 8-5. 

Compounds of metals and alkyl or aryl groups are frequently spontaneously ignitible in air, especially the lower members of homologous scries, such as the methyl and ethyl compounds. The metals in the most active compounds are the alkali metals and aluminum, zinc, and arsenic. The nonmetals boron and phosphorus also furnish active members, which conventionally are classed with the metal-organic (sometimes called organo-metallic) compounds. It is noteworthy that the alkyls of silicon do not flame in air. 

At this point boron is tite only other element left to consider in our survey of tite nonmetals. Boron is the only element of group 3A that can be considered non-metallic. The element has an extended network structure. Its melting point (2300°C) is intermediate between that of carbon (3550 C) and that of silicon (1410°C). The electron configuration of boron is [He]2s 2p. ... 

Compounds containing fluorine and chlorine are also donors to BF3. Aqueous fluoroboric acid and the tetrafluoroborates of metals, nonmetals, and organic radicals represent a large class of compounds in which the fluoride ion is coordinating with trifluoroborane. Representative examples of these compounds are given in Table 5. Coordination compounds of boron trifluoride with the chlorides of sodium, aluminum, iron, copper, 2inc, tin, and lead have been indicated (53) they are probably chlorotrifluoroborates. 

Alkoxides of nonmetals are described in articles about the corresponding compounds (see Boron COMPOUNDS, Boron oxides Silicon compounds). Metal alkyls, in which the alkyl group is bound direcdy to the metal, are also discussed elsewhere (see Aluminum compounds). 

Boron [7440-42-8] B, is unique in that it is the only nonmetal in Group 13 (IIIA) of the Periodic Table. Boron, at wt 10.81, at no. 5, has more similarity to carbon and siUcon than to the other elements in Group 13. There are two stable boron isotopes, B and B, which are naturally present at 19.10—20.31% and 79.69—80.90%, respectively. The range of the isotopic abundancies reflects a variabiUty in naturally occurring deposits such as high B ore from Turkey and low °B ore from California. Other boron isotopes, B, B, and B, have half-Hves of less than a second. The B isotope has a very high cross-section for absorption of thermal neutrons, 3.835 x 10 (3835 bams). This neutron absorption produces alpha particles. 

The main metals in brines throughout the world are sodium, magnesium, calcium, and potassium. Other metals, such as lithium and boron, are found in lesser amounts. The main nonmetals ate chloride, sulfate, and carbonate, with nitrate occurring in a few isolated areas. A significant fraction of sodium nitrate and potassium nitrate comes from these isolated deposits. Other nonmetals produced from brine ate bromine and iodine. 

The diagonal line or stairway that starts to the left of boron in the periodic table (Figure 2.7, page 31) separates metals from nonmetals. The more than 80 elements to the left and below that line, shown in blue in the table, have the properties of metals in particular, they have high electrical conductivities. Elements above and to the right of the stairway are nonmetals (yellow) about 18 elements fit in that category. 

FIGURE B.12 The location ot the seven elements commonly regarded as metalloids these elements have characteristics of both metals and nonmetals. Other elements, notably beryllium and bismuth, are sometimes included in the classification. Boron (B), although not resembling a metal in appearance, is included because it resembles silicon (Si) chemically. 

These studies show that radon can be classified as a metalloid element, together with boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine. Like these elements, radon lies on the diagonal of the Periodic Table between the true metals and nonmetals (Figure 5) and exhibits some of the characteristics of both (Stein, 1985). 

The elements on the right side of the chart have more electrons j in their outer shells than those on the left, but their nuclei hold I them more tightly. Only the elements in Groups IV and V that have large atoms permit enough free electron movement for them to behave as metals. A diagonal line drawn down the chart from boron to bismuth divides the metals from the nonmetals. None of the elements above the line are metallic. 

In addition to functioning as Lewis acids, boron halides undergo many other types of reactions. As is typical of most compounds containing covalent bonds between a nonmetal and a halogen, the boron halides react vigorously with water to yield boric acid and the corresponding hydrogen halide. 

A boron Both elements are nonmetals. This is a binary molecular compound BF3... 

Nonmetal hydrides Boron trifluoride, phosphorus trichloride, silicon tetrachloride... 

Some of the metalloids are considered semiconductors. The term metalloids is used in this reference book because these elements do have characteristics of both metals and non-metals, and the term semiconductor refers only to particular elements somewhere between metals and nonmetals. Semiconductors also have properties of both metals and nonmetals. Therefore, they have the ability to act as conductors of electricity and thermal energy (heat), as well as the ability to act as insulators or nonconductors of electricity and heat, depending upon the kind and amount of impurities their crystals contain. Again, following the zigzag steps on the periodic table, the metalloids having properties of both metals and nonmetals are as follows boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. 

Boron has only three electrons in its outer shell, which makes it more metal than nonmetal. Nonmetals have four or more electrons in their valence shell. Even so, boron is somewhat related to metalloids and also to nonmetals in period 2. 

Boron is a semimetal, sometimes classed as a metallic or metalloid or even as a nonmetal. It resembles carbon more closely than aluminum, the latter of which is located just below boron in group 13. Although it is extremely hard in its purified form—almost as hard as diamonds—it is more brittle than diamonds, thus limiting its usefulness. It is an excellent conductor of electricity at high temperatures, but acts as an insulator at lower temperatures. It is less reactive than the elements below it in group 13... 

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