25 - Chemistry 1000 Lecture 25: Group 14 and Boron Marc R....

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Chemistry 1000 Lecture 25: Group 14 and Boron Marc R. Roussel
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Group 14 I In this group again, we see a full range of nonmetallic to metallic behavior: C is a nonmetal. Si and Ge are metalloids. Sn and Pb are metals. I Carbon is the central element in most biomolecules. Also widely distributed as carbonate minerals (many of biological origin), coal, graphite and diamond. Also present in atmosphere as CO 2 (seasonally averaged current value of 392 ppm, rising by about 2 ppm/year) I Si is the second most abundant element in the Earth’s crust (after O), mostly present in nature as silicon oxide (sand and related materials), quartz and silicate minerals. I Sn and Pb are fairly abundant metals. Principal ores: SnO 2 , PbS, PbSO 4 and PbCO 3
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Allotropes of carbon I Most stable allotrope: graphite I Moderately good electrical conductor, but its conductivity is anisotropic (different in different directions) in single crystals I Diamond I Insulator I Hardest naturally occurring substance I Metastable at normal pressures I Fullerenes, carbon nanotubes
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Graphite I Graphite structure: stacked sheets + resonance structures I Stacking:
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25 - Chemistry 1000 Lecture 25: Group 14 and Boron Marc R....

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