114440707-Chemistry.docx - Properties Physical properties...

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PropertiesPhysical properties of organic compounds typically of interest include bothquantitative and qualitative features. Quantitative information includes meltingpoint, boiling point, and index of refraction. Qualitative properties include odor,consistency, solubility, and color.Melting and boiling propertiesIn contrast to many inorganic materials, organic compounds typically melt andmany boil. In earlier times, the melting point (m.p.) and boiling point (b.p.) providedcrucial information on the purity and identity of organic compounds. The meltingand boiling points correlate with the polarity of the molecules and their molecularweight. Some organic compounds, especially symmetrical ones, sublime, that isthey evaporate without melting. A well known example of a sublimable organiccompound ispara-dichlorobenzene, the odiferous constituent of modern mothballs.Organic compounds are usually not very stable at temperatures above 300 °C,although some exceptions exist.SolubilityNeutral organic compounds tend to be hydrophobic, that is they are lesssolubleinwater than in organic solvents. Exceptions include organic compounds that containionizable groups as well as lowmolecular weightalcohols,amines, andcarboxylicacidswherehydrogen bondingoccurs. Organic compounds tend to dissolve inorganicsolvents. Solvents can be either pure substances likeetherorethyl alcohol,or mixtures, such as the paraffinic solvents such as the variouspetroleumethersandwhite spirits, or the range of pure or mixed aromatic solvents obtainedfrom petroleum or tarfractionsby physical separation or by chemical conversion.Solubility in the different solvents depends upon the solvent type and onthefunctional groupsif present.Solid state propertiesVarious specialized properties ofmolecular crystalsandorganicpolymerswithconjugated systemsare of interest depending on applications, e.g.thermo-mechanical and electro-mechanical such aspiezoelectricity, electricalconductivity (seeconductive polymersandorganic semiconductors), and electro-optical (e.g.non-linear optics) properties. For historical reasons, such propertiesare mainly the subjects of the areas ofpolymer scienceandmaterials science.Diamondis one well known allotrope of carbon. The hardness and high dispersionof light of diamond make it useful for both industrial applications and jewellery.Diamond is the hardest known naturalmineral. This makes it an excellent abrasiveand makes it hold polish and luster extremely well. No known naturally occurringsubstance can cut (or even scratch) a diamond, except another diamond.Graphite(named byAbraham Gottlob Wernerin 1789, from the Greek γράφειν(graphein, "to draw/write", for its use in pencils) is one of the most commonallotropes of carbon. Unlike diamond, graphite is an electrical conductor. Thus, itcan be used in, for instance, electrical arc lamp electrodes. Likewise,understandard conditions, graphite is the most stable form of carbon. Therefore, itis used in thermochemistry as the

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