Physical Properties Of Alkenes

Alkenes chemistry is a study of carbon compounds which are held together by a double bond. These are unsaturated carbon compounds which have a general formula of CnH2n. These compounds are also known as olefins. The physical properties possessed by these double-bonded compounds are similar to the physical properties of alkanes.

These double bonded compounds are colourless and odourless in nature. However, Ethene is an exception as it is a colourless gas but has a faint sweet odour. The first three members of the alkene group are gaseous in nature, next fourteen members are liquids and the remaining alkenes are solids. The alkenes are insoluble in water but are completely soluble in non-polar solvents such as benzene, ligroin to name a few.

 The boiling points of the compounds increase as the number of carbon atoms in the compound increases. When alkenes are compared with alkanes, it is evident that the boiling points of both are almost similar if the compounds are made up of the same carbon skeleton. The boiling point of straight chain alkenes is more that branched chain alkenes just as in alkanes.

The melting points of these double-bonded compounds depends upon the positioning of the molecules. The melting point of alkenes is similar to that of alkanes. However, cis-isomer molecules have a lower melting point than trans- isomers as the molecules are packed in a U-bending shape.

Alkenes are weakly polar just like alkanes but are slightly more reactive than alkanes due to the presence of double bonds. The π electrons which make up the double bonds can easily be removed or added as they are weakly held. Hence the dipole moments exhibited by alkenes are more than alkanes. The polarity depends upon the functional group attached to the compounds and the chemical structures.

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Practise This Question

Ethene when treated with Br2 in the presence of CCl4 which compound is formed