Learning OutcomesDescribe the general preparation, properties, and also uses that the metalloidsDescribe the preparation, properties, and compounds the boron and silicon
A collection of six aspects called the metalloids different the steels from the nonmetals in the periodic table. The metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium. These facets look metallic; however, they do not conduct electricity as well as metals for this reason they are semiconductors. They are semiconductors since their electron are much more tightly tied to your nuclei than space those that metallic conductors. Your chemical habits falls between that of metals and also nonmetals. Because that example, the pure metalloids form covalent crystals favor the nonmetals, however like the metals, they typically do not form monatomic anions. This intermediate habits is in component due to their intermediate electronegativity values. In this section, we will certainly briefly discuss the chemical behavior of metalloids and address two of this elements—boron and silicon—in more detail.
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The metalloid boron exhibits plenty of similarities to its neighborhood carbon and also its diagonal neighbor silicon. All 3 elements kind covalent compounds. However, boron has one distinct distinction in that its 2s22p1 external electron structure gives it one much less valence electron than it has actually valence orbitals. Although boron exhibits one oxidation state the 3+ in most of its secure compounds, this electron deficiency gives boron with the capacity to type other, occasionally fractional, oxidation states, i m sorry occur, because that example, in the boron hydrides.
Silicon has the valence covering electron configuration 3s23p2, and also it commonly forms tetrahedral structures in which that is sp3 hybridized v a formal oxidation state that 4+. The significant differences between the chemistry the carbon and also silicon result from the relative strength the the carbon-carbon bond, carbon’s capacity to form stable bonds to itself, and the existence of the north 3d valence-shell orbitals in silicon. Silicon’s empty d orbitals and boron’s north p orbital enable tetrahedral silicon compounds and trigonal planar boron compounds to act together Lewis acids. Carbon, ~ above the various other hand, has no easily accessible valence shell orbitals; tetrahedral carbon compounds cannot act as Lewis acids. Germanium is very similar to silicon in its chemistry behavior.
Arsenic and antimony generally form compounds in i m sorry an oxidation state of 3+ or 5+ is exhibited; however, arsenic can kind arsenides v an oxidation state of 3-. These facets tarnish just slightly in dried air yet readily oxidize when warmed.
Tellurium combines directly with most elements. The most stable tellurium compounds room the tellurides—salts the Te2- developed with energetic metals and also lanthanides—and compounds v oxygen, fluorine, and chlorine, in which tellurium generally exhibits one oxidation state 2+ or 4+. Return tellurium(VI) compounds are recognized (for example, TeF6), there is a marked resistance come oxidation come this maximum team oxidation state.
Structures of the Metalloids
Covalent bonding is the crucial to the crystal frameworks of the metalloids. In this regard, these elements resemble nonmetals in your behavior.
Elemental silicon, germanium, arsenic, antimony, and also tellurium space lustrous, metallic-looking solids. Silicon and also germanium crystallize with a diamond structure. Every atom in ~ the crystal has covalent bonds to 4 neighboring atoms at the corners the a continual tetrahedron. Solitary crystals of silicon and germanium are giant, three-dimensional molecules. There are several allotropes the arsenic through the many stable gift layer like and containing puckered sheets of arsenic atoms. Each arsenic atom creates covalent bonds to three other atoms in ~ the sheet. The crystal framework of antimony is similar to that of arsenic, both presented in Figure 1. The frameworks of arsenic and antimony are similar to the structure of graphite, covered later in this chapter. Tellurium forms crystals that contain infinite spiral chain of tellurium atoms. Each atom in the chain bonds come two various other atoms.
Explore a cubic diamond decision structure. (Note that the video has no narration. Friend can accessibility the audio description using the widget listed below the video.)
You have the right to view the transcript because that the audio summary of “Face centered Cubic structure (diamond)” below (opens in brand-new window).
Figure 1. (a) Arsenic and (b) antimony have actually a layered structure comparable to the of (c) graphite, except that the layers are puckered fairly than planar. (d) element tellurium forms spiral chains.
Figure 2. One icosahedron is a symmetrical, solid shape with 20 faces, each of i m sorry is an it is provided triangle. The encounters meet at 12 corners.
Pure crystalline boron is transparent. The crystals covers icosahedra, as shown in Figure 2, through a boron atom at every corner. In the most common kind of boron, the icosahedra load together in a manner similar to the cubic closest pack of spheres. All boron-boron binding within each icosahedron room identical and are about 176 pm in length. In the various forms the boron, there are different arrangements and also connections in between the icosahedra.
The surname silicon is acquired from the Latin word because that flint, silex. The metalloid silicon readily develops compounds containing Si-O-Si bonds, which room of prime prestige in the mineral world. This bonding capacity is in contrast to the nonmetal carbon, whose capacity to kind carbon-carbon bonds offers it prime prestige in the plant and animal worlds.
Occurrence, Preparation, and also Compounds that Boron and 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 also in dried lake regions, including the desert areas of California, together borates and salts that boron oxyacids, such together borax, Na2B4O7•10H2O.
Elemental boron is chemically inert at room temperature, reaction with just fluorine and oxygen to kind boron trifluoride, BF3, and also boric oxide, B2O3, respectively. At greater temperatures, boron reacts through all nonmetals, other than tellurium and also the noble gases, and also with practically all metals; the oxidizes come B2O3 when heated with concentrated nitric or sulfuric acid. Boron does not react through nonoxidizing acids. Plenty of boron compounds react conveniently with water to provide boric acid, B(OH)3 (sometimes composed as H3BO3).
Reduction of boric oxide through magnesium powder develops boron (95–98.5% pure) as a brown, amorphous powder:
An amorphous problem is a product that appears to it is in a solid, yet does not have actually a long-range order prefer a true solid. Treatment with hydrochloric acid removes the magnesium oxide. Additional purification the the boron starts with conversion of the impure boron right into boron trichloride. The following step is to warm a mixture the boron trichloride and hydrogen:
Silicon provides up practically one-fourth of the massive of the earth’s crust—second in abundance just to oxygen. The crust is composed almost entirely of minerals in which the silicon atoms space at the facility of the silicon-oxygen tetrahedron, which affix in a variety of methods to produce, among other things, chains, layers, and three-dimensional frameworks. These minerals constitute the mass of most typical rocks, soil, and clays. In addition, products such together bricks, ceramics, and glasses save on computer silicon compounds.
It is possible to produce silicon by the high-temperature reduction of silicon dioxide with solid reducing agents, such together carbon and magnesium:
Figure 3. A zone-refining apparatus provided to to wash silicon.
Extremely pure silicon is crucial for the manufacture of semiconductor digital devices. This procedure begins with the conversion of impure silicon into silicon tetrahalides, or silane (SiH4), followed by decomposition at high temperatures. Region refining, depicted in Figure 3, completes the purification. In this method, a stick of silicon is heated in ~ one finish by a heat source that produce a thin cross-section that molten silicon. Slowly lowering the rod through the heat resource moves the molten zone from one finish of the rod to other. Together this thin, molten region moves, impurities in the silicon dissolve in the fluid silicon and move through the molten region. Ultimately, the impurities move to one end of the rod, i beg your pardon is then cut off.
This highly purified silicon, containing no more than one component impurity every million parts of silicon, is the most important aspect in the computer system industry. Pure silicon is vital in semiconductor electronic tools such as transistors, computer system 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 soluble in warm aqueous base; thus, strong bases damage the passivation. Removed of the passivation layer permits the base to dissolve the silicon, developing hydrogen gas and silicate anions. Because that example:
Silicon reacts v halogens at high temperatures, forming volatile tetrahalides, such together SiF4.
Unlike carbon, silicon go not conveniently form double or triple bonds. Silicon link of the general formula SiX4, where X is a extremely electronegative group, can act together Lewis mountain to form six-coordinate silicon. For example, silicon tetrafluoride, SiF4, reacts with sodium fluoride to productivity Na2
Antimony reacts easily with stoichiometric amounts of fluorine, chlorine, bromine, or iodine, yielding trihalides or, v excess fluorine or chlorine, developing the pentahalides SbF5 and also SbCl5. Depending upon the stoichiometry, it creates antimony(III) sulfide, Sb2S3, or antimony(V) sulfide when heated with sulfur. As expected, the metallic nature the the element is higher than that of arsenic, i m sorry lies immediately above it in group 15.
Boron and also Silicon Halides
Boron trihalides—BF3, BCl3, BBr3, and also BI3—can be prepared by the direct reaction the the elements. These nonpolar molecules contain boron through sp2 hybridization and a trigonal planar molecular geometry. The fluoride and also chloride compounds room colorless gasses, the bromide is a liquid, and the iodide is a white crystalline solid.
Except for boron trifluoride, the boron trihalides readily hydrolyze in water to kind boric acid and also the equivalent hydrohalic acid. Boron trichloride reacts according come the equation:
Boron trifluoride reacts v hydrofluoric acid, to productivity a systems of fluoroboric acid, HBF4:
In this reaction, the BF3 molecule acts together the Lewis mountain (electron pair acceptor) and also accepts a pair of electron from a fluoride ion:
All the tetrahalides the silicon, SiX4, have been prepared. Silicon tetrachloride deserve to be all set by direct chlorination in ~ elevated temperatures or by heating silicon dioxide with chlorine and also carbon:
Silicon tetrachloride is a covalent tetrahedral molecule, i beg your pardon is a nonpolar, low-boiling (57 °C), colorless liquid.
It is feasible to prepare silicon tetrafluoride through the reaction the silicon dioxide through hydrofluoric acid:
Hydrofluoric mountain is the only usual acid that will react v silicon dioxide or silicates. This reaction occurs because the silicon-fluorine shortcut is the only bond the silicon creates that is stronger than the silicon-oxygen bond. Because that this reason, that is possible to save all usual acids, other than hydrofluoric acid, in glass containers.
Except for silicon tetrafluoride, silicon halides are very sensitive to water. Upon exposure to water, SiCl4 reacts quickly with hydroxide groups, replacing all four chlorine atom to create unstable orthosilicic acid, Si(OH)4 or H4SiO4, which gradually decomposes right into SiO2.
Boron and also Silicon Oxides and also Derivatives
Boron burns at 700 °C in oxygen, forming boric oxide, B2O3. Boric oxide is vital for the manufacturing of heat-resistant borosilicate glass, favor that shown in Figure 4 and certain optical glasses. Boric oxide dissolves in warm water to type boric acid, B(OH)3:
Figure 4. Activities glassware, such as Pyrex and also Kimax, is make of borosilicate glass due to the fact that it does not break as soon as heated. The inclusion of borates in the glass helps to convey the results of thermal expansion and contraction. This to reduce the likelihood of heat shock, which causes silicate glass to cracked upon quick heating or cooling. (credit: “Tweenk”/Wikimedia Commons)
Figure 5. Boric acid has a planar framework with 3 –OH teams spread out equally at 120° angle from every other.
The boron atom in B(OH)3 is sp2 hybridized and is situated at the facility of an equilateral triangle v oxygen atoms at the corners. In hard B(OH)3, hydrogen bonding holds this triangular devices together. Boric acid, displayed in Figure 5, is a an extremely weak mountain that does not act as a proton donor but rather as a Lewis acid, accepting an unshared pair of electrons from the Lewis base OH–:
Heating boric mountain to 100 °C reasons molecules the water to separation out in between pairs of adjacent –OH groups to form metaboric acid, HBO2. At around 150 °C, additional B-O-B linkages form, connecting the BO3 groups in addition to shared oxygen atoms to form tetraboric acid, H2B4O7. Finish water loss, at still greater temperatures, outcomes in boric oxide.
Borates space salts of the oxyacids the boron. Borates an outcome from the reactions of a base with an oxyacid or indigenous the blend of boric acid or boric oxide through a metal oxide or hydroxide. Borate anions variety from the straightforward trigonal planar
Figure 6. The borate anions space (a) CaB2O4, (b) KB5O8•4H2O, and (c) Na2B4O7•10H2O. The anion in CaB2O4 is one “infinite” chain.
Silicon dioxide, silica, wake up in both crystalline and also amorphous forms. The normal crystalline type of silicon dioxide is quartz, a hard, brittle, clear, colorless solid. It is helpful in many ways—for architectural decorations, semiprecious jewels, and frequency control in radio transmitters. Silica takes numerous crystalline forms, or polymorphs, in nature. Trace quantities of Fe3+ in quartz give amethyst that characteristic violet color. The ax quartz is also used for articles such together tubing and also lenses that are made from amorphous silica. Opal is a normally occurring type of amorphous silica.
The comparison in structure and also physical properties between silicon dioxide and carbon dioxide is interesting, as illustrated in Figure 7. Heavy carbon dioxide (dry ice) contains single CO2 molecules v each the the 2 oxygen atoms attached come the carbon atom by double bonds. Really weak intermolecular pressures hold the molecules together in the crystal. The volatility that dry ice cream reflect this weak forces between molecules. In contrast, silicon dioxide is a covalent network solid. In silicon dioxide, every silicon atom web links to 4 oxygen atom by solitary bonds directed toward the corners of a continual tetrahedron, and SiO4 tetrahedra re-superstructure oxygen atoms. This plan gives a three dimensional, continuous, silicon-oxygen network. A quartz crystal is a macromolecule the silicon dioxide. The difference between these two compounds is the capability of the group 14 facets to kind strong π bonds. Second-period elements, such as carbon, kind very solid π bonds, i m sorry is why carbon dioxide forms little molecules through strong twin bonds. Facets below the second period, such together silicon, execute not kind π bond as conveniently as second-period elements, and also when they perform form, the π bonds are weaker than those created by second-period elements. Because that this reason, silicon dioxide does not contain π bonds yet only σ bonds.
Figure 7. Due to the fact that carbon has tendency to form dual and triple bonds and silicon walk not, (a) carbon dioxide is a discrete molecule through two C=O dual bonds and also (b) silicon dioxide is an unlimited network the oxygen atom bridging between silicon atoms with each silicon atom possessing 4 Si-O single bonds. (credit a photo: change of work by Erica Gerdes; credit transaction b photo: change of job-related by Didier Descouens)
At 1600 °C, quartz melts to productivity a viscous liquid. As soon as the fluid cools, the does no crystallize readily yet usually supercools and forms a glass, likewise called silica. The SiO4 tetrahedra in glassy silica have a random plan characteristic the supercooled liquids, and also the glass has actually some an extremely useful properties. Silica is extremely transparent to both visible and ultraviolet light. Because that this reason, it is crucial in the produce of lamps that give radiation wealthy in ultraviolet light and also in details optical instruments that operate with ultraviolet light. The coefficient of growth of silica glass is an extremely low; therefore, fast temperature transforms do not reason it to fracture. CorningWare and other ceramic cookware contain amorphous silica.
Silicates space salts include anions composed of silicon and also oxygen. In almost all silicates, sp3-hybridized silicon atoms occur at the centers the tetrahedra through oxygen in ~ the corners. Over there is a sports in the silicon-to-oxygen proportion that occurs since silicon-oxygen tetrahedra might exist as discrete, independent units or might share oxygen atoms at corners in a selection of ways. In addition, the existence of a selection of cations provides rise come the big number that silicate minerals.
Many ceramics are composed the silicates. By including small amounts of various other compounds, it is possible to change the physical properties that the silicate materials to create ceramics with valuable characteristics.
Key Concepts and also Summary
The elements boron, silicon, germanium, arsenic, antimony, and also tellurium different the steels from the nonmetals in the routine table. These elements, called metalloids or periodically semimetals, exhibit nature characteristic that both metals and also nonmetals. The structures of these aspects are similar in many ways come those of nonmetals, however the elements are electrical semiconductors.
Try ItGive the hybridization that the metalloid and the molecule geometry because that each of the adhering to compounds or ions. You might wish to testimonial the chapters on chemistry bonding and progressed covalent bonding for relevant examples.GeH4SbF3Te(OH)6H2TeGeF2TeCl4
2. The Lewis framework for each is as follows:H3BPH3:
4. 1s22s22p63s23p23d0. The thorough configuration because that the valence shell is:
6. The hybridization the silicon and the molecular framework of each is as follows:(CH3)3SiH: sp3 bonding about Si; the structure is tetrahedral
8. (a) nonpolar; (b) nonpolar; (c) polar; (d) nonpolar; (e) polar
10. (a) tellurium dioxide or tellurium(IV) oxide; (b) antimony(III) sulfide; (c) germanium(IV) fluoride; (d) silane or silicon(IV) hydride; (e) germanium(IV) hydride
12. Boron has only s and p orbitals available, which have the right to accommodate a preferably of 4 electron pairs. Unlike silicon, no d orbitals are available in boron.
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ΔG° = -969.01 + 2(-273) – (-1120.3) – 3(-237.18) = 44 kJ;
ΔG° = -969.01 + 3(-95.299) – (-388.7) – 3(-237.18) = -154.7 kJ;
ΔG° = 2(-969.01) + 0 – 86.6 – 6(-237.18) = -601.5 kJ
16. A mild systems of hydrofluoric would certainly dissolve the silicate and would not harm the diamond.
amorphous: solid material such together a glass the does not have actually a continual repeating component to that three-dimensional structure; a solid yet not a crystal
boratecompound include boron-oxygen bonds, commonly with swarm or chains as a component of the chemical structure
polymorph: variation in crystalline structure that results in various physical properties because that the result compound
silicate: compound include silicon-oxygen bonds, with silicate tetrahedra linked in rings, sheets, or three-dimensional networks, relying on the other facets involved in the development of the compounds