Learning OutcomesDescribe the general preparation, properties, and uses of the metalloidsDescribe the preparation, properties, and also compounds the boron and also silicon
A collection of six elements called the metalloids separate the metals from the nonmetals in the regular table. The metalloids space boron, silicon, germanium, arsenic, antimony, and tellurium. These facets look metallic; however, they perform not command electricity and also metals for this reason they room semiconductors. They space semiconductors due to the fact that their electrons are much more tightly tied to your nuclei than space those the metallic conductors. Their chemical habits falls between that the metals and also nonmetals. Because that example, the pure metalloids form covalent crystals prefer the nonmetals, but like the metals, they normally do not kind monatomic anions. This intermediate actions is in part due to your intermediate electronegativity values. In this section, we will certainly briefly discuss the chemical behavior of metalloids and attend to two of these elements—boron and silicon—in much more detail.
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The metalloid boron exhibits countless similarities come its neighborhood carbon and also its diagonal neighbor silicon. All 3 elements type covalent compounds. However, boron has actually one distinct distinction in that its 2s22p1 external electron structure gives it one less valence electron 보다 it has valence orbitals. Although boron exhibits one oxidation state the 3+ in many of its secure compounds, this electron deficiency offers boron with the ability to type other, sometimes fractional, oxidation states, i beg your pardon occur, because that example, in the boron hydrides.
Silicon has the valence covering electron construction 3s23p2, and also it generally forms tetrahedral frameworks in which it is sp3 hybridized v a officially oxidation state the 4+. The major differences between the chemistry that carbon and silicon an outcome from the loved one strength of the carbon-carbon bond, carbon’s capability to type stable bonds come itself, and also the presence of the north 3d valence-shell orbitals in silicon. Silicon’s north d orbitals and also boron’s north p orbital permit tetrahedral silicon compounds and trigonal planar boron compounds come act as Lewis acids. Carbon, ~ above the other hand, has actually no accessible valence covering orbitals; tetrahedral carbon compounds cannot act together Lewis acids. Germanium is very comparable to silicon in its chemistry behavior.
Arsenic and also antimony generally type compounds in i beg your pardon an oxidation state the 3+ or 5+ is exhibited; however, arsenic can kind arsenides through an oxidation state the 3-. These elements tarnish only slightly in dried air however readily oxidize as soon as warmed.
Tellurium combines directly with many elements. The most stable tellurium compounds room the tellurides—salts that Te2- formed with energetic metals and lanthanides—and compounds with oxygen, fluorine, and also chlorine, in i m sorry tellurium usually exhibits one oxidation state 2+ or 4+. Although tellurium(VI) compound are recognized (for example, TeF6), over there is a marked resistance to oxidation come this maximum group oxidation state.
Structures the the Metalloids
Covalent bonding is the vital to the crystal frameworks of the metalloids. In this regard, these elements resemble nonmetals in your behavior.
Elemental silicon, germanium, arsenic, antimony, and tellurium are lustrous, metallic-looking solids. Silicon and germanium crystallize v a diamond structure. Every atom within the crystal has actually covalent bond to 4 neighboring atom at the corners that a continuous tetrahedron. Solitary crystals of silicon and also germanium are giant, three-dimensional molecules. Over there are numerous allotropes that arsenic v the most stable gift layer like and containing puckered sheets that arsenic atoms. Each arsenic atom creates covalent bonds come three various other atoms within the sheet. The crystal structure of antimony is similar to the of arsenic, both shown in Figure 1. The frameworks of arsenic and also antimony are similar to the structure of graphite, covered later on in this chapter. Tellurium creates crystals that contain boundless spiral chain of tellurium atoms. Each atom in the chain bonds come two other atoms.
Explore a cubic diamond decision structure. (Note that the video clip has no narration. You can accessibility the audio summary 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, other than that the layers room puckered fairly than planar. (d) element tellurium forms spiral chains.
Figure 2. An icosahedron is a symmetrical, solid form with 20 faces, each of i m sorry is an equilateral 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 each corner. In the most common type of boron, the icosahedra pack together in a manner similar to the cubic closest pack of spheres. Every boron-boron binding within every icosahedron space identical and are around 176 afternoon in length. In the different forms the boron, over there are various arrangements and connections in between the icosahedra.
The name silicon is acquired from the Latin word because that flint, silex. The metalloid silicon readily forms compounds containing Si-O-Si bonds, which space of prime prestige in the mineral world. This bonding ability is in contrast to the nonmetal carbon, whose capacity to form carbon-carbon bonds provides it prime prominence in the plant and animal worlds.
Occurrence, Preparation, and Compounds of Boron and Silicon
Boron constitutes much less than 0.001% by load of the earth crust. In nature, it only occurs in compounds v oxygen. Boron is widely dispersed in volcanic areas as boric acid, B(OH)3, and also in dry lake regions, consisting of the desert areas of California, as borates and also salts the 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 the noble gases, and also with practically all metals; that oxidizes come B2O3 when heated with concentrated nitric or sulfuric acid. Boron does no react v nonoxidizing acids. Countless boron compounds react readily with water to give boric acid, B(OH)3 (sometimes created as H3BO3).
Reduction the boric oxide v magnesium powder forms boron (95–98.5% pure) as a brown, amorphous powder:
An amorphous problem is a material that shows up to it is in a solid, but does not have a long-range order prefer a true solid. Treatment with hydrochloric acid clears the magnesium oxide. Further purification of the boron starts with counter of the impure boron into boron trichloride. The following step is to warmth a mixture the boron trichloride and also hydrogen:
Silicon makes up practically one-fourth of the fixed of the earth crust—second in abundance just to oxygen. The late is composed practically entirely of mineral in i m sorry the silicon atoms are at the center of the silicon-oxygen tetrahedron, which connect in a selection of ways to produce, among other things, chains, layers, and also three-dimensional frameworks. These minerals constitute the bulk of most common rocks, soil, and also clays. In addition, products such together bricks, ceramics, and also glasses contain silicon compounds.
It is possible to develop 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 produce of semiconductor digital devices. This procedure begins with the counter of impure silicon right into silicon tetrahalides, or silane (SiH4), adhered to by decomposition in ~ high temperatures. Ar refining, depicted in Figure 3, completes the purification. In this method, a pole of silicon is heated at one end by a heat resource that produces a thin cross-section the molten silicon. Progressively lowering the rod v the heat resource moves the molten zone from one finish of the rod come other. As this thin, molten region moves, impurities in the silicon dissolve in the fluid silicon and move v the molten region. Ultimately, the impurities move to one finish of the rod, i beg your pardon is then reduced off.
This highly purified silicon, include no more than one component impurity every million components of silicon, is the many important facet in the computer system industry. Pure silicon is important in semiconductor electronic tools such as transistors, computer system chips, and solar cells.
Like part metals, passivation the silicon wake up due the formation of a very thin film of oxide (primarily silicon dioxide, SiO2). Silicon dioxide is dissolve in warm aqueous base; thus, strong bases damage the passivation. Remove of the passivation layer allows the basic to dissolve the silicon, creating hydrogen gas and silicate anions. Because that example:
Silicon reacts through halogens in ~ high temperatures, creating volatile tetrahalides, such as SiF4.
Unlike carbon, silicon go not easily form twin or triple bonds. Silicon link of the basic formula SiX4, whereby X is a highly electronegative group, deserve to act as Lewis mountain to kind six-coordinate silicon. Because that example, silicon tetrafluoride, SiF4, reacts through sodium fluoride to productivity Na2
Antimony reacts easily with stoichiometric amounts of fluorine, chlorine, bromine, or iodine, yielding trihalides or, through excess fluorine or chlorine, creating the pentahalides SbF5 and also SbCl5. Depending on the stoichiometry, it creates antimony(III) sulfide, Sb2S3, or antimony(V) sulfide when heated through sulfur. As expected, the metallic nature that the facet is greater than that of arsenic, i m sorry lies immediately above it in team 15.
Boron and also Silicon Halides
Boron trihalides—BF3, BCl3, BBr3, and BI3—can be prepared by the direct reaction that the elements. This nonpolar molecules contain boron through sp2 hybridization and also a trigonal planar molecule geometry. The fluoride and 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 easily hydrolyze in water to type boric acid and also the equivalent hydrohalic acid. Boron trichloride reacts according to the equation:
Boron trifluoride reacts through hydrofluoric acid, to yield a solution of fluoroboric acid, HBF4:
In this reaction, the BF3 molecule acts as the Lewis mountain (electron pair acceptor) and accepts a pair of electrons from a fluoride ion:
All the tetrahalides of silicon, SiX4, have actually been prepared. Silicon tetrachloride can be prepared by straight chlorination at elevated temperatures or by heater silicon dioxide with chlorine and carbon:
Silicon tetrachloride is a covalent tetrahedral molecule, i m sorry is a nonpolar, low-boiling (57 °C), colorless liquid.
It is possible to prepare silicon tetrafluoride by the reaction the silicon dioxide with hydrofluoric acid:
Hydrofluoric mountain is the only typical acid that will certainly react v silicon dioxide or silicates. This reaction occurs since the silicon-fluorine shortcut is the only bond the silicon creates that is stronger than the silicon-oxygen bond. For this reason, it is feasible to store all typical acids, other than hydrofluoric acid, in glass containers.
Except for silicon tetrafluoride, silicon halides are exceptionally sensitive come water. Top top exposure come water, SiCl4 reacts rapidly with hydroxide groups, replacing all four chlorine atoms to produce unstable orthosilicic acid, Si(OH)4 or H4SiO4, which gradually decomposes right into SiO2.
Boron and Silicon Oxides and also Derivatives
Boron burns at 700 °C in oxygen, forming boric oxide, B2O3. Boric oxide is essential for the manufacturing of heat-resistant borosilicate glass, like that shown in Figure 4 and specific 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 made of borosilicate glass since it does no break as soon as heated. The consists of borates in the glass helps to adjust the impacts of heat expansion and also contraction. This reduce the likelihood of thermal shock, which reasons silicate glass to crack upon fast heating or cooling. (credit: “Tweenk”/Wikimedia Commons)
Figure 5. Boric acid has a planar structure with 3 –OH groups spread the end equally in ~ 120° angle from every other.
The boron atom in B(OH)3 is sp2 hybridized and is situated at the center of an it is intended triangle with oxygen atoms at the corners. In solid B(OH)3, hydrogen bonding holds these triangular devices together. Boric acid, displayed in Figure 5, is a an extremely weak acid that does no act as a proton donor yet rather as a Lewis acid, agree an unshared pair of electron from the Lewis base OH–:
Heating boric acid to 100 °C reasons molecules that water to break-up out in between pairs of nearby –OH groups to kind metaboric acid, HBO2. At around 150 °C, added B-O-B linkages form, connecting the BO3 groups in addition to shared oxygen atom to type tetraboric acid, H2B4O7. Complete water loss, in ~ still greater temperatures, results in boric oxide.
Borates space salts that the oxyacids the boron. Borates an outcome from the reaction of a base through an oxyacid or native the blend of boric acid or boric oxide with a steel oxide or hydroxide. Borate anions selection from the straightforward trigonal planar
Figure 6. The borate anions are (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 also amorphous forms. The usual crystalline form of silicon dioxide is quartz, a hard, brittle, clear, colorless solid. It is helpful in countless ways—for architecture decorations, semiprecious jewels, and also frequency control in radio transmitters. Silica takes plenty of crystalline forms, or polymorphs, in nature. Trace quantities of Fe3+ in quartz give amethyst that is characteristic violet color. The ax quartz is additionally used for short articles such as tubing and lenses that are manufactured from amorphous silica. Opal is a normally occurring kind of amorphous silica.
The contrast in structure and also physical properties in between silicon dioxide and carbon dioxide is interesting, as shown in Figure 7. Solid carbon dioxide (dry ice) contains single CO2 molecules through each of the two oxygen atoms attached come the carbon atom by twin bonds. Really weak intermolecular pressures hold the molecules with each other in the crystal. The volatility that dry ice cream reflect these weak forces in between molecules. In contrast, silicon dioxide is a covalent network solid. In silicon dioxide, each silicon atom links to four oxygen atom by solitary bonds directed toward the corners that a continual tetrahedron, and also SiO4 tetrahedra share oxygen atoms. This plan gives a three dimensional, continuous, silicon-oxygen network. A quartz decision is a macromolecule the silicon dioxide. The difference between these two compounds is the ability of the group 14 facets to type strong π bonds. Second-period elements, such as carbon, form very strong π bonds, i beg your pardon is why carbon dioxide forms small molecules through strong twin bonds. Facets below the 2nd period, such together silicon, execute not kind π bonds as conveniently as second-period elements, and when they do form, the π bonds are weaker 보다 those developed by second-period elements. Because that this reason, silicon dioxide does no contain π bonds however only σ bonds.
Figure 7. Due to the fact that carbon often tends to form twin and triple bonds and also silicon does not, (a) carbon dioxide is a discrete molecule with two C=O twin bonds and (b) silicon dioxide is an boundless network that 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 b photo: change of job-related by Didier Descouens)
At 1600 °C, quartz melts to yield a viscous liquid. When the liquid cools, it does not crystallize readily however usually supercools and also forms a glass, also called silica. The SiO4 tetrahedra in glassy silica have actually a random plan characteristic the supercooled liquids, and also the glass has some an extremely useful properties. Silica is extremely transparent come both visible and ultraviolet light. Because that this reason, the is crucial in the manufacture of lamps that offer radiation well-off in ultraviolet light and in details optical instruments that run with ultraviolet light. The coefficient of growth of silica glass is very low; therefore, rapid temperature transforms do not cause it come fracture. CorningWare and also other ceramic cookware save on computer amorphous silica.
Silicates are salts comprise anions created of silicon and also oxygen. In almost all silicates, sp3-hybridized silicon atoms take place at the centers that tetrahedra v oxygen at the corners. There is a sports in the silicon-to-oxygen ratio that occurs because silicon-oxygen tetrahedra might exist as discrete, independent systems or may share oxygen atom at corners in a variety of ways. In addition, the visibility of a range of cations offers rise to the huge number of silicate minerals.
Many ceramics space composed of silicates. Through including small amounts of other compounds, that is possible to modify the physical properties the the silicate products to create ceramics with helpful characteristics.
Key Concepts and Summary
The aspects boron, silicon, germanium, arsenic, antimony, and tellurium different the metals from the nonmetals in the regular table. This elements, dubbed metalloids or periodically semimetals, exhibit nature characteristic the both metals and nonmetals. The frameworks of these aspects are similar in many ways to those that nonmetals, however the facets are electric semiconductors.
Try ItGive the hybridization the the metalloid and also the molecular geometry because that each of the following compounds or ions. You may wish to evaluation the chapters on chemical bonding and advanced covalent bonding for pertinent examples.GeH4SbF3Te(OH)6H2TeGeF2TeCl4
2. The Lewis structure for each is together follows:H3BPH3:
4. 1s22s22p63s23p23d0. The in-depth configuration for the valence covering is:
6. The hybridization of silicon and the molecular structure of each is together follows:(CH3)3SiH: sp3 bonding around 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 deserve to accommodate a maximum of 4 electron pairs. Uneven silicon, no d orbitals are easily accessible 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 equipment of hydrofluoric would dissolve the silicate and also would not damage the diamond.
amorphous: solid product such as a glass that does not have a continual repeating ingredient to that three-dimensional structure; a solid yet not a crystal
boratecompound include boron-oxygen bonds, frequently with clusters or chains as a component of the chemistry structure
polymorph: variation in crystalline structure that results in different physical properties for the resulting compound
silicate: compound containing silicon-oxygen bonds, with silicate tetrahedra linked in rings, sheets, or three-dimensional networks, relying on the other aspects involved in the development of the compounds