Alkenes

Alkenes

Introduction

  • Alkenes are also a type of hydrocarbon like alkanes, but they contain a carbon-carbon double bond.
  • This double bond makes them unsaturated.
  • The general formula for alkenes is CnH2n, where ‘n’ represents the number of carbon atoms.

Structure and Properties

  • In alkenes, at least two carbon atoms are bonded together by a double bond, while other carbon and hydrogen atoms are bonded by single covalent bonds.
  • The presence of the carbon-carbon double bond causes alkenes to have different physical and chemical properties compared to alkanes.
  • The carbon-carbon double bond is an area of high electron density, making alkenes more reactive than alkanes.
  • Similar to alkanes, alkenes are also insoluble in water due to their non-polar nature, but they can dissolve in organic solvents.

Examples

  • Examples of alkenes include: ethene (C2H4), propene (C3H6), and butene (C4H8).

Reactions

  • Alkenes undergo addition reactions due to the carbon-carbon double bond.
  • For instance, they react with hydrogen in hydrogenation reactions to form alkanes.
  • Another significant reaction of alkenes is with halogens, called halogenation, in which the halogen adds across the double bond.
  • Alkenes also burn in air or oxygen to give carbon dioxide and water, but the combustion is often incomplete, leading to carbon monoxide and soot (carbon).

Uses of Alkenes

  • Alkenes are used widely in the chemical industry, especially in the production of polymers or plastics.
  • Ethene is used in the manufacturing of poly(ethene) - often known as polythene.
  • They are also used to manufacture a range of other chemicals, many of which are used to produce consumer goods, such as detergents, solvents or high-octane fuels.

Environmental Impact

  • Like alkanes, burning alkenes also produces carbon dioxide, a greenhouse gas contributing to global warming.
  • Incomplete combustion producing carbon monoxide can be particularly dangerous as it is a poisonous gas.
  • Large scale manufacture and use of alkenic polymers (plastics) pose significant environmental issues due to their non-biodegradable nature.

Remember, learning more about alkenes, their properties, reactions, and environmental impacts will strengthen your understanding of organic chemistry and help you appreciate the role these compounds play in our everyday lives.