Chapter 22- Alkanes

• Alkanes are hydrocarbons that contain only single covalent bonds between carbon atoms.

• They have the general formula: CnH2n+2

• A structural formula is the formula which shows how atoms are arranged in a molecule.

• Alkanes are saturated hydrocarbons because they contain only single carbon-carbon bond.

  

ISOMERISM

• Compounds that have the same molecular formula but different structural formula are isomers.

• Branched alkyl groups are isomers of alkanes.

  

PROPERTIES OF ALKANES

• As alkane molecules get bigger, the attractive forces become stronger.
• Melting and boiling points, and density of alkanes increases as their molecular sizes increases.
• Viscosity also increases as it becomes difficult to pour out bigger molecule chains.
• The flammability decreases as the carbon chains become longer.
• Complete combustion of alkanes produces carbon dioxide and water while incomplete combustion produces carbon monoxide and water.

CRACKING

• Longer chains of alkanes are broken down to smaller chains of hydrocarbons which are more in demand. This process is cracking.

SUBSTITUTION REACTIONS

• Alkanes are generally unreactive but they react with halogens.

• One mole of chlorine substitutes one hydrogen atom. Another product of hydrogen chloride is formed.

  

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