A series of six elements called the metalloids different the metals from the nonmetals in the routine table. The metalloids room boron, silicon, germanium, arsenic, antimony, and tellurium. These facets look metallic; however, they execute not conduct electricity and also metals therefore they room semiconductors. They room semiconductors because their electron are an ext tightly bound to your nuclei than space those of metallic conductors. Their gaianation.netical habits falls in between that that metals and also nonmetals. For example, the pure metalloids form covalent crystals choose the nonmetals, yet like the metals, they normally do not form monatomic anions. This intermediate habits is in part due to your intermediate electronegativity values. In this section, we will briefly talk about the gaianation.netical actions of metalloids and attend to two of this elements—boron and silicon—in an ext detail.
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The metalloid boron exhibits many similarities come its neighborhood carbon and also its diagonal line neighbor silicon. All three elements kind covalent compounds. However, boron has actually one distinct difference in the its 2s22p1 outer electron structure gives it one less valence electron than it has actually valence orbitals. Return boron exhibits an oxidation state of 3+ in many of its stable compounds, this electron deficiency offers boron v the ability to type other, occasionally fractional, oxidation states, i beg your pardon occur, because that example, in the boron hydrides.
Silicon has the valence covering electron configuration 3s23p2, and it commonly forms tetrahedral structures in which that is sp3 hybridized v a formal oxidation state the 4+. The major differences between the gaianation.netistry of carbon and also silicon result from the family member strength that the carbon-carbon bond, carbon’s capability to type stable bonds to itself, and also the presence of the north 3d valence-shell orbitals in silicon. Silicon’s north d orbitals and also boron’s empty p orbital permit tetrahedral silicon compounds and trigonal planar boron compounds come act as Lewis acids. Carbon, ~ above the other hand, has actually no available valence shell orbitals; tetrahedral carbon compounds cannot act as Lewis acids. Germanium is very comparable to silicon in that is gaianation.netical behavior.
Arsenic and antimony generally form compounds in i beg your pardon an oxidation state the 3+ or 5+ is exhibited; however, arsenic can kind arsenides v an oxidation state that 3−. These facets tarnish just slightly in dry air however readily oxidize as soon as warmed.
Tellurium combines straight with most elements. The most stable tellurium compounds room the tellurides—salts that Te2− created with energetic metals and also lanthanides—and compounds v oxygen, fluorine, and chlorine, in i beg your pardon tellurium generally exhibits one oxidation state 2+ or 4+. Return tellurium(VI) compounds are known (for example, TeF6), over there is a marked resistance to oxidation to this maximum team oxidation state.
Structures the the Metalloids
Covalent bonding is the key to the crystal frameworks of the metalloids. In this regard, these elements resemble nonmetals in your behavior.
Occurrence, Preparation, and Compounds of Boron and also Silicon
Boron constitutes much less than 0.001% by weight of the earth’s crust. In nature, it only occurs in compounds with oxygen. Boron is widely distributed in volcanic areas as boric acid, B(OH)3, and in dried lake regions, consisting of the desert locations of California, together borates and also salts of boron oxyacids, such as borax, Na2B4O7⋅10H2O.
Elemental boron is gaianation.netically inert in ~ room temperature, reacting with only fluorine and also oxygen to type boron trifluoride, BF3, and also boric oxide, B2O3, respectively. At greater temperatures, boron reacts v all nonmetals, other than tellurium and also the noble gases, and with practically all metals; that oxidizes to B2O3 once heated with concentrated nitric or sulfuric acid. Boron does no react with nonoxidizing acids. Many boron compounds react easily with water to give boric acid, B(OH)3 (sometimes composed as H3BO3).
Reduction that boric oxide through magnesium powder creates boron (95–98.5% pure) together a brown, amorphous powder:
An amorphous problem is a material that shows up to be a solid, however does not have a long-range order choose a true solid. Treatment with hydrochloric acid removes the magnesium oxide. More purification that the boron begins with conversion of the impure boron into boron trichloride. The next step is to heat a mixture that boron trichloride and hydrogen:
\<\ce2BCl3(g)+\ce3H2(g)\:\mathrm\xrightarrow1500\:°C\:\ce2B(s)+\ce6HCl(g) \hspace20px ΔH°=\mathrm253.7\: kJ\>
Silicon renders up virtually one-fourth the the mass of the earth’s crust—second in abundance only to oxygen. The late is composed nearly entirely of minerals in which the silicon atoms room at the center of the silicon-oxygen tetrahedron, which connect in a variety of means to produce, among other things, chains, layers, and also three-dimensional frameworks. These minerals constitute the bulk of most typical rocks, soil, and also clays. In addition, materials such together bricks, ceramics, and glasses save on computer silicon compounds.
It is possible to develop silicon by the high-temperature reduction of silicon dioxide with strong reducing agents, such as carbon and also magnesium:
Extremely pure silicon is important for the to produce of semiconductor digital devices. This process begins v the switch of impure silicon right into silicon tetrahalides, or silane (SiH4), complied with by decomposition in ~ high temperatures. Region refining, shown in number \(\PageIndex3\), completes the purification. In this method, a pole of silicon is heated at one finish by a heat resource that produce a slim cross-section that molten silicon. Progressively lowering the rod v the heat source moves the molten zone from one finish of the rod to other. As this thin, molten region moves, impurities in the silicon dissolve in the liquid silicon and move v the molten region. Ultimately, the impurities move to one end of the rod, i beg your pardon is then cut off.
This extremely purified silicon, comprise no an ext than one component impurity per million parts of silicon, is the most important element in the computer system industry. Pure silicon is crucial in semiconductor electronic tools such as transistors, computer chips, and also solar cells.
Like part metals, passivation that silicon wake up due the development of a an extremely thin movie of oxide (primarily silicon dioxide, SiO2). Silicon dioxide is dissolve in hot aqueous base; thus, solid bases ruin the passivation. Removal of the passivation layer enables the basic to dissolve the silicon, creating hydrogen gas and also silicate anions. For example:
Silicon reacts with halogens in ~ high temperatures, creating volatile tetrahalides, such together SiF4.
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Unlike carbon, silicon does not conveniently form twin or triple bonds. Silicon link of the general formula SiX4, whereby X is a very electronegative group, deserve to act as Lewis acids to type six-coordinate silicon. Because that example, silicon tetrafluoride, SiF4, reacts with sodium fluoride to yield Na2
Antimony reacts easily with stoichiometric quantities of fluorine, chlorine, bromine, or iodine, yielding trihalides or, with excess fluorine or chlorine, forming the pentahalides SbF5 and SbCl5. Relying on the stoichiometry, it forms antimony(III) sulfide, Sb2S3, or antimony(V) sulfide as soon as heated with sulfur. Together expected, the metallic nature the the aspect is better than that of arsenic, i beg your pardon lies immediately above it in team 15.