Physical Properties of Alkenes

Alkenes containĀ a carbon-carbon double bond which changes the physical properties of alkenes. Alkenes are unsaturated carbon compounds which have a general formula of CnH2n. 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.

Table of Contents

Physical Properties of Alkenes

1. Physical State

        • These double-bonded compounds are colourless and odourless in nature.
        • However, ethene is an exception because it is a colourless gas with a faintly sweet odour.
        • The first three members of the alkene group are gaseous in nature, the next fourteen members are liquids and the remaining alkenes are solids.

2. Solubility

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

3. 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 than branched-chain alkenes just as in alkanes.

4.Ā 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.

5. Polarity

        • Alkenes are weakly polar just like alkanes but are slightly more reactive than alkanes due to the presence of double bonds.
        • The Ļ€ 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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Frequently Asked Questions ā€“ FAQs

Q1

Why alkenes are insoluble in water?

Due to their non-polar properties, alkenes are lighter than water and insoluble in water. Alkenes can only be dissolved in nonpolar solvents.
Q2

What are the first 5 alkenes?

The following is a list of the first five Alkenes:

  • Propene (C3H6)
  • Butene (C4H8)
  • Pentene (C5H10)
  • Hexene (C6H12)
  • Heptene (C7H14)
Q3

Why does cis have lower melting point than trans?

Trans isomers pack better than cis isomers. Cis isomers pack poorly, which means that the intermolecular forces arenā€™t as effective as they should be and thus less amount of energy is required to melt the cis molecule. Hence, cis molecules have lower melting point.

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  1. Very good

  2. EXCEPTIONALLY GOOD!!!

  3. umm nice

  4. really understandable

  5. really good, do you have notes for the physical properties of alkanes??