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Which of the following is a molecular crystalline solids?A. GraphiteB. DiamondC. FullereneD. None of these |
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Answer» Correct Answer - 3 Graphite and diamond are covalent network solids.Graphite,the most common allotrope of carbon and the most stable under normal conditions, is a cystalline covalent network solids that consists of two -dimensional sheets of fused six-membered rings . Each `C` atom is `sp^(3)` . hybrized and is bonded with tetrahedral geometry to three other carbons. The diamond form of elementals carbon is a covalent network solids in which each carbon atom is `sp^(3)` hybrized and is bonded with tetrahedral geometry to four other carbons. In addition to graphite and diamond a third, crystalline allotrope of carbon called Buckminster fullerene was discovered in `1985` as a constituent of soot.Fullerence is a molcular sold consisting of spherical `C_(60)` molcules with the extraordinary shpae of soccor ball ,the `C_(60)` ball has `12` pentagonal and `20` hexagonal faces ,with each `C` atom `sp^(2)` hybrodized and bonded graphite and fullerence are a group of carbon allotropes called nanotubes Carbon nanotubes are tubular structures made of repeating six-membered rings ,as if a sheet of graphite were rolled up .Typically the tubes have a diameter of about `2-30`nm and a length of up to `1mm`. Graphite is the black, slippery substance used as the "lead" in pencils as an electrode material in batteies and as a lubricant in locks.All these propeties result from its sheet like structure ,Air and water molecules can adsorb onto the flat faces of the sheets,allowing the sheets to slide over one another and givning grphite its greasy felling and lubricating properties . Graphite is mores stable than diamond at normal pressures.(on account of the possibility of resonance ) but can be converted into diamond at very high pressure .Some industrial diamonds are now made from graphite by applying `150,000` atm presuure at high temperatures. Fullerence ,black and shiny like graphite is the subject of active current research becuase of fits interesting electronic propertied,When allowed to react with `Rb` metal a superconduting material called rubidium fulleride `Rb_(3)60` is formed .Carbon nanotubes are being studued for use as fibre in the structural composites used to make gold clubs ,bicycle frames,boats and airplanes.On a mass basis,nanutubes are upt to tne times as strong as steel. |
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