Learning OutcomesDescribe the general preparation, properties, and also uses the the metalloidsDescribe the preparation, properties, and also compounds the boron and also silicon
A collection of six aspects called the metalloids different the metals from the nonmetals in the regular table. The metalloids room boron, silicon, germanium, arsenic, antimony, and also tellurium. These aspects look metallic; however, they carry out not command electricity as well as metals for this reason they room semiconductors. They room semiconductors because their electron are an ext tightly tied to their nuclei than room those the metallic conductors. Their chemical actions falls between that of metals and also nonmetals. Because that example, the pure metalloids form covalent crystals like the nonmetals, yet like the metals, they normally do not form monatomic anions. This intermediate actions is in component due to their intermediate electronegativity values. In this section, we will certainly briefly talk about the chemical actions of metalloids and address two of these elements—boron and also silicon—in more detail.
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The metalloid boron exhibits plenty of similarities come its neighbor 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 provides it one less valence electron 보다 it has actually valence orbitals. Although boron exhibits an oxidation state of 3+ in most of its steady compounds, this electron deficiency gives boron v the capability to form other, occasionally fractional, oxidation states, which occur, for example, in the boron hydrides.
Silicon has actually the valence shell electron construction 3s23p2, and it generally forms tetrahedral structures in which it is sp3 hybridized with a formal oxidation state of 4+. The significant differences in between the chemistry of carbon and also silicon result from the relative strength of the carbon-carbon bond, carbon’s ability to kind stable bonds come itself, and also the existence of the north 3d valence-shell orbitals in silicon. Silicon’s north d orbitals and boron’s north p orbital permit tetrahedral silicon compounds and also trigonal planar boron compounds come act together Lewis acids. Carbon, on the other hand, has actually no available valence shell orbitals; tetrahedral carbon compounds can not act together Lewis acids. Germanium is very comparable to silicon in its chemistry behavior.
Arsenic and also antimony generally kind compounds in i beg your pardon an oxidation state that 3+ or 5+ is exhibited; however, arsenic can form arsenides through an oxidation state that 3-. These aspects tarnish just slightly in dry air however readily oxidize when warmed.
Tellurium combines directly with most elements. The most stable tellurium compounds space the tellurides—salts the Te2- developed with active metals and also lanthanides—and compounds with oxygen, fluorine, and chlorine, in i m sorry tellurium usually exhibits an oxidation state 2+ or 4+. Although tellurium(VI) link are well-known (for example, TeF6), over there is a significant resistance to oxidation come this maximum team oxidation state.
Structures that the Metalloids
Covalent bonding is the an essential to the crystal structures of the metalloids. In this regard, these elements resemble nonmetals in their behavior.
Elemental silicon, germanium, arsenic, antimony, and also tellurium are lustrous, metallic-looking solids. Silicon and also germanium crystallize with a diamond structure. Every atom in ~ the crystal has covalent bonds to 4 neighboring atom at the corners of a regular tetrahedron. Single crystals of silicon and germanium room giant, three-dimensional molecules. Over there are several allotropes the arsenic with the most stable being layer like and also containing puckered sheets the arsenic atoms. Each arsenic atom develops covalent bonds to three various other atoms in ~ the sheet. The crystal structure of antimony is similar to that of arsenic, both presented in Figure 1. The structures of arsenic and also antimony are comparable to the structure of graphite, covered later in this chapter. Tellurium creates crystals the contain boundless spiral chain of tellurium atoms. Every atom in the chain bonds come two various other atoms.
Explore a cubic diamond decision structure. (Note the the video clip has no narration. You can access the audio description using the widget below the video.)
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Figure 1. (a) Arsenic and also (b) antimony have a layered structure comparable to that of (c) graphite, except that the layers space puckered quite than planar. (d) element tellurium develops spiral chains.
Figure 2. One icosahedron is a symmetrical, solid shape with 20 faces, every of i beg your pardon is an equilateral triangle. The encounters meet in ~ 12 corners.
Pure crystalline boron is transparent. The crystals consists icosahedra, as shown in Figure 2, through a boron atom at each corner. In the many common form of boron, the icosahedra fill together in a manner comparable to the cubic closest packing of spheres. Every boron-boron binding within each icosahedron room identical and also are about 176 pm in length. In the various forms of boron, over there are various arrangements and also connections in between the icosahedra.
The surname silicon is obtained from the Latin word for flint, silex. The metalloid silicon readily develops compounds include Si-O-Si bonds, which space of prime prestige in the mineral world. This bonding capability is in comparison to the nonmetal carbon, whose ability to kind carbon-carbon bonds gives it prime importance in the plant and animal worlds.
Occurrence, Preparation, and also Compounds the Boron and also Silicon
Boron constitutes much less than 0.001% by load of the earth’s crust. In nature, it only occurs in compounds v oxygen. Boron is widely dispersed in volcanic regions as boric acid, B(OH)3, and in dried lake regions, including the desert locations of California, together borates and also salts that boron oxyacids, such as borax, Na2B4O7•10H2O.
Elemental boron is chemically inert at room temperature, reacting with only fluorine and also oxygen to form boron trifluoride, BF3, and boric oxide, B2O3, respectively. At higher temperatures, boron reacts with all nonmetals, other than tellurium and also the noble gases, and with almost all metals; the oxidizes to B2O3 once heated with concentrated nitric or sulfuric acid. Boron does no react v nonoxidizing acids. Many boron compound react easily with water to offer boric acid, B(OH)3 (sometimes composed as H3BO3).
Reduction that boric oxide through magnesium powder forms boron (95–98.5% pure) as a brown, amorphous powder:
An amorphous substance is a product that appears to be a solid, but does not have a long-range order choose a true solid. Treatment with hydrochloric acid gets rid of the magnesium oxide. Additional purification of the boron begins with switch of the impure boron into boron trichloride. The following step is to warmth a mixture the boron trichloride and hydrogen:
Silicon makes up practically one-fourth that the fixed of the earth’s crust—second in abundance only to oxygen. The crust is composed virtually entirely of minerals in i m sorry the silicon atoms are at the center of the silicon-oxygen tetrahedron, which attach in a range of means to produce, amongst other things, chains, layers, and also three-dimensional frameworks. This minerals constitute the bulk of most typical rocks, soil, and also clays. In addition, products such as bricks, ceramics, and glasses save on computer silicon compounds.
It is feasible to create silicon through the high-temperature reduction of silicon dioxide with solid reducing agents, such as carbon and magnesium:
Figure 3. A zone-refining apparatus supplied to purify silicon.
Extremely pure silicon is necessary for the to produce of semiconductor electronic devices. This procedure begins through the counter of impure silicon into silicon tetrahalides, or silane (SiH4), adhered to by decomposition at high temperatures. Region refining, shown in Figure 3, completes the purification. In this method, a pole of silicon is heated in ~ one finish by a heat resource that produces a thin cross-section that molten silicon. Slowly lowering the rod v the heat source moves the molten zone native one finish of the rod come other. Together this thin, molten an ar moves, impurities in the silicon dissolve in the liquid silicon and also move with the molten region. Ultimately, the impurities relocate to one end of the rod, i beg your pardon is then reduced off.
This very purified silicon, include no much more than one component impurity per million parts of silicon, is the most important element in the computer industry. Pure silicon is vital in semiconductor electronic devices such as transistors, computer chips, and also solar cells.
Like some metals, passivation that silicon occurs due the development of a really thin movie of oxide (primarily silicon dioxide, SiO2). Silicon dioxide is dissolve in warm aqueous base; thus, strong bases damage the passivation. Removed of the passivation layer permits the base to dissolve the silicon, forming hydrogen gas and also silicate anions. For example:
Silicon reacts through halogens at high temperatures, creating volatile tetrahalides, such as SiF4.
Unlike carbon, silicon does not conveniently form dual or triple bonds. Silicon compound of the basic formula SiX4, whereby X is a extremely electronegative group, have the right to act together Lewis mountain to kind six-coordinate silicon. For example, silicon tetrafluoride, SiF4, reacts v sodium fluoride to yield Na2
Antimony reacts readily with stoichiometric amounts of fluorine, chlorine, bromine, or iodine, yielding trihalides or, v excess fluorine or chlorine, creating the pentahalides SbF5 and also SbCl5. Depending upon the stoichiometry, it creates antimony(III) sulfide, Sb2S3, or antimony(V) sulfide once heated with sulfur. As expected, the metallic nature of the facet is greater than the of arsenic, i m sorry lies immediately over it in team 15.
Boron and Silicon Halides
Boron trihalides—BF3, BCl3, BBr3, and also BI3—can be ready by the straight reaction the the elements. This nonpolar molecule contain boron v sp2 hybridization and also a trigonal planar molecular geometry. The fluoride and also chloride compounds space colorless gasses, the bromide is a liquid, and the iodide is a white crystalline solid.
Except for boron trifluoride, the boron trihalides conveniently hydrolyze in water to kind boric acid and also the corresponding hydrohalic acid. Boron trichloride reaction according to the equation:
Boron trifluoride reacts through hydrofluoric acid, to productivity a systems of fluoroboric acid, HBF4:
In this reaction, the BF3 molecule acts together the Lewis acid (electron pair acceptor) and also accepts a pair of electrons from a fluoride ion:
All the tetrahalides the silicon, SiX4, have been prepared. Silicon tetrachloride can be prepared by straight chlorination at elevated temperature or by heating silicon dioxide through 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 possible to prepare silicon tetrafluoride by the reaction of silicon dioxide with hydrofluoric acid:
Hydrofluoric acid 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 develops that is stronger than the silicon-oxygen bond. For this reason, the is possible to keep all usual acids, other than hydrofluoric acid, in glass containers.
Except for silicon tetrafluoride, silicon halides are exceptionally sensitive to water. ~ above exposure come water, SiCl4 reacts rapidly with hydroxide groups, instead of all 4 chlorine atoms to produce unstable orthosilicic acid, Si(OH)4 or H4SiO4, which slowly decomposes into SiO2.
Boron and Silicon Oxides and Derivatives
Boron burns in ~ 700 °C in oxygen, forming boric oxide, B2O3. Boric oxide is crucial for the manufacturing of heat-resistant borosilicate glass, like that displayed in Figure 4 and certain optical glasses. Boric oxide disappear in warm water to type boric acid, B(OH)3:
Figure 4. Laboratory glassware, such together Pyrex and Kimax, is made of borosilicate glass due to the fact that it does no break once heated. The consists of borates in the glass help to convey the impacts of heat expansion and also contraction. This reduce the likelihood of heat shock, which causes silicate glass to cracked upon fast heating or cooling. (credit: “Tweenk”/Wikimedia Commons)
Figure 5. Boric acid has a planar framework with three –OH groups spread out equally at 120° angle from every other.
The boron atom in B(OH)3 is sp2 hybridized and is located at the facility of an it is intended triangle through oxygen atoms at the corners. In solid B(OH)3, hydrogen bonding holds this triangular devices together. Boric acid, shown in Figure 5, is a an extremely weak acid that does no act together a proton donor but rather together a Lewis acid, accepting an unshared pair of electron from the Lewis basic OH–:
Heating boric acid to 100 °C reasons molecules of water to separation out in between pairs of nearby –OH teams to form metaboric acid, HBO2. At about 150 °C, additional B-O-B linkages form, connecting the BO3 groups along with shared oxygen atom to form tetraboric acid, H2B4O7. Complete water loss, at still higher temperatures, outcomes in boric oxide.
Borates space salts of the oxyacids of boron. Borates result from the reactions of a base through an oxyacid or from the combination of boric mountain or boric oxide with a metal oxide or hydroxide. Borate anions variety from the simple trigonal planar
Figure 6. The borate anions room (a) CaB2O4, (b) KB5O8•4H2O, and also (c) Na2B4O7•10H2O. The anion in CaB2O4 is an “infinite” chain.
Silicon dioxide, silica, wake up in both crystalline and amorphous forms. The usual crystalline type of silicon dioxide is quartz, a hard, brittle, clear, colorless solid. The is beneficial in plenty of ways—for architectural decorations, semiprecious jewels, and also frequency manage in radio transmitters. Silica takes numerous crystalline forms, or polymorphs, in nature. Trace amounts of Fe3+ in quartz provide amethyst its characteristic violet color. The ax quartz is likewise used for short articles such together tubing and also lenses the are made from amorphous silica. Opal is a normally occurring kind of amorphous silica.
The comparison in structure and physical properties between silicon dioxide and carbon dioxide is interesting, as illustrated in Figure 7. Solid carbon dioxide (dry ice) contains solitary CO2 molecules with each of the two oxygen atom attached to the carbon atom by twin bonds. An extremely weak intermolecular pressures hold the molecules with each other in the crystal. The volatility that dry ice reflect this weak forces in between molecules. In contrast, silicon dioxide is a covalent network solid. In silicon dioxide, every silicon atom web links to four oxygen atom by single bonds directed toward the corners of a continuous tetrahedron, and SiO4 tetrahedra re-publishing oxygen atoms. This setup gives a 3 dimensional, continuous, silicon-oxygen network. A quartz decision is a macromolecule of silicon dioxide. The difference in between these two compounds is the capability of the team 14 facets to form strong π bonds. Second-period elements, such as carbon, type very strong π bonds, i beg your pardon is why carbon dioxide forms tiny molecules through strong twin bonds. Elements below the second period, such as silicon, execute not form π binding as readily as second-period elements, and also when they do form, the π bonds are weaker 보다 those developed 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 tends to form dual and triple bonds and also silicon walk not, (a) carbon dioxide is a discrete molecule v two C=O dual bonds and (b) silicon dioxide is an infinite network that oxygen atom bridging in between silicon atoms v each silicon atom possessing four Si-O single bonds. (credit a photo: change of job-related by Erica Gerdes; credit transaction b photo: alteration of occupational by Didier Descouens)
At 1600 °C, quartz melts to yield a viscous liquid. Once the liquid cools, that does not crystallize readily but usually supercools and forms a glass, also called silica. The SiO4 tetrahedra in glassy silica have a random plan characteristic the supercooled liquids, and also the glass has actually some really useful properties. Silica is extremely transparent to both visible and also ultraviolet light. Because that this reason, that is important in the produce of lamps that offer radiation rich in ultraviolet light and in particular optical tools that run with ultraviolet light. The coefficient of growth of silica glass is an extremely low; therefore, fast temperature transforms do not cause it to fracture. CorningWare and also other ceramic cookware contain amorphous silica.
Silicates space salts comprise anions composed of silicon and also oxygen. In nearly all silicates, sp3-hybridized silicon atoms take place at the centers that tetrahedra v oxygen in ~ the corners. Over there is a sport in the silicon-to-oxygen proportion that occurs because silicon-oxygen tetrahedra may exist as discrete, independent systems or might share oxygen atom at corners in a range of ways. In addition, the presence of a selection of cations offers rise come the large number the silicate minerals.
Many ceramics are composed that silicates. By including small amounts of various other compounds, it is feasible to change the physical properties the the silicate products to create ceramics with valuable characteristics.
Key Concepts and also Summary
The elements boron, silicon, germanium, arsenic, antimony, and tellurium separate the steels from the nonmetals in the regular table. These elements, referred to as metalloids or occasionally semimetals, exhibit nature characteristic the both metals and also nonmetals. The frameworks of these elements are similar in plenty of ways to those of nonmetals, however the aspects are electrical semiconductors.
Try ItGive the hybridization the the metalloid and also the molecule geometry for each the the adhering to compounds or ions. You might wish to testimonial the chapters on chemistry bonding and advanced covalent bonding for relevant examples.GeH4SbF3Te(OH)6H2TeGeF2TeCl4
2. The Lewis framework for each is together follows:H3BPH3:
4. 1s22s22p63s23p23d0. The in-depth configuration for the valence covering is:
6. The hybridization that silicon and also the molecular structure of every 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 actually only s and p orbitals available, which can accommodate a maximum of 4 electron pairs. Uneven silicon, no d orbitals are obtainable 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 solution of hydrofluoric would certainly dissolve the silicate and also would not harm the diamond.
amorphous: solid material such as a glass that does not have a continual repeating ingredient to the three-dimensional structure; a solid but not a crystal
boratecompound include boron-oxygen bonds, frequently with swarm or chains as a part of the chemistry structure
polymorph: variation in crystalline framework that results in different physical properties because that the result compound
silicate: compound include silicon-oxygen bonds, with silicate tetrahedra connected in rings, sheets, or three-dimensional networks, depending on the other aspects involved in the development of the compounds