Physical Properties of Alkenes

Introduction

Physical Properties of Alkenes

Alkenes contain a carbon-carbon double bond which changes the physical properties of alkenes. Alkenes are unsaturated carbon compounds which have a general formula of \(C_nH_{2n}\)..These compounds are also known as olefins. Alkenes are a family of compounds containing hydrogen and carbon only (hydrocarbons) with a carbon-carbon double bond. Ethene and Propene are the first two hydrocarbons.

Physical State

These double bonded compounds are colorless and odorless in nature. However, ethene is an exception because it is a colorless gas but has a faintly sweet odor. The first three members of the alkene group are gaseous in nature, next fourteen members are liquids and the remaining alkenes are solids.

Solubility

The alkenes are insoluble in water due to their nonpolar characteristics. But are completely soluble in nonpolar solvents such as benzene, ligroin, etc.

Boiling Point

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 found that the boiling points of both are almost similar, as 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.

Melting point

The melting points of these double-bonded compounds depend 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.

Polarity

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

Identify the term that is generally used to express the quality of a gasoline.