Chapter 12 main component in rocks sand planetary

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Chapter 12 -Main component in rocks, sand, planetary crust for terrestrial planets;also clays, mica, talc, glass, gemstonesHuge number of compounds where silicate anion is compensated byvarious cationsSiO2(silica)polymorphicforms are quartz, crystobalite, & tridymiteThe strong Si-O bonds lead to a high melting temperature (1710ºC)for this material30Silicate CeramicsSi4+O2-Adapted from Figs.12.9-10,Callister &Rethwisch 8ecrystobaliteorthosilicate
1/21/20206Chapter 12 -Main component in rocks, sand, planetary crust for terrestrial planets;also clays, mica, talc, glass, gemstonesHuge number of compounds where silicate anion is compensated byvarious cationsSiO2(silica)polymorphicforms are quartz, crystobalite, & tridymiteThe strong Si-O bonds lead to a high melting temperature (1710ºC)for this material31Silicate Ceramicscrystobalitediamond cubic structureChapter 12 - 32Bonding of adjacentSiO44-accomplished by thesharing of common corners, edges, or facesSilicatesMg2SiO4Ca2MgSi2O7Adapted from Fig.12.12,Callister &Rethwisch 8e.Presence of cations such as Ca2+, Mg2+, & Al3+1.maintain charge neutrality, and2.ionically bond SiO44-to one anotherChapter 12 - 33Quartz iscrystallineSiO2:Basic Unit:Glass is noncrystalline (amorphous?)Fused silica is SiO2to which no impuritieshave been addedOther common glasses contain impurityions such as Na+, Ca2+, Al3+, and B3+(soda glass)Adapted from Fig. 12.11,Callister & Rethwisch 8e.Glass StructureSi4+Na+O2-orthosilicateShort + medium-range order present,disorder beyond that.Other oxides, e.g., GeO2, also form glassesChapter 12 - 34Layered Silicates (Phyllosilicates)Layered silicates (e.g., clays, mica, talc)SiO4tetrahedra connectedtogether to form 2-D planeA net negative charge is associatedwith each (Si2O5)2-unitNegative charge balanced byadjacent plane rich in positivelycharged cationsAdapted from Fig.12.13,Callister &Rethwisch 8e.Chapter 12 - 35Kaolinite clay alternates (Si2O5)2-layer with Al2(OH)42+layerLayered Silicates: Kaolinite and othersNote:Adjacent sheets of this type are loosely bound toone another by van der Waal’s forces.Adapted from Fig. 12.14,Callister & Rethwisch 8e.Chapter 12 - 36Layered Silicates: Kaolinite and others
1/21/20207Chapter 12 - 37Polymorphic Forms of CarbonDiamond (sp3)– tetrahedral bonding ofcarbonhardest material knownvery high thermalconductivitylarge single crystals –gem stonessmall crystals – used togrind/cut other materials– diamond thin filmshard surface coatings –used for cutting tools,medical devices, etc.Adapted from Fig. 12.15,Callister & Rethwisch 8e.diamond cubic structure:like zinc blende, but bothsites have the same ionicspecies (C or Si)Chapter 12 - 38Polymorphic Forms of Carbon (cont)Graphite (sp2within layers + vdW between)– layered structure – parallel hexagonal arrays ofcarbon atoms– strong covalent bonding within each layerweak van der Waals forces between layers– planes slide easily over one another -- good lubricant– electrically conductiveAdapted from Fig.

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