Physical Properties of some Organic compounds

Summary of the Physical properties of...

  • Alkanes
  • Alkenes
  • Halogenoalkanes
  • Alcohols
  • Carboxylic acids

    Not hugely detailes, these are just for recap, but hope they're useful :D 

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Physical properties: ALKANES

  • Non polar --> Unable to dissolve in water (hydrophobic)
  • Boiling points rise as the number of carbon atoms per molecule increases (more bonds to break- greater attraction between molecules).
  • Alkanes in the range of one to four carbons are gases at room temperature
  • Alkanes in the range of five to seventeen carbons are liquids at room temperature (the more carbons, the more viscous the liquid)
  • C----H bonds only
  • General formula ---> CnH(2n+2)
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Physical properties: ALKENES

  • Non polar --> Do not dissolve in water (Hydrophobic)
  • Boiling point increases as the number of carbon atoms in the molecule increases
  • Physical properties (Melting/boiling points etc) of Alkenes very similar to those of Alkanes of similar chain length
  • Contains double bond
  • General Formula --> CnH(2n)
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Physical properties: HALOGENOALKANES

  • Most halogenoalkanes are colourless liquids at room temperature (Chloromethane, Bromomethane and Chloroethane are gases at room temperature)
  • Most halogenoalkanes are hydrophobic
  • Longer chains = higher melting and boiling points
  • Size/number of the Halogen atom affects melting/boiling points- Iodoalkanes have higher melting/boiling points than Chloroalkanes as the atoms are bigger (unless there are many Chlorines to few Iodines)
  • Chains contain one or more halogen--carbon bonds. Position of the halogen is indicated by numbers preceding equation (2, 3 chloropentane means there are chlorine atoms bonded to the 2nd and 3rd carbon. It doesn't matter whether you count the carbons from the right or left, as if you flipped the molecule they would be in the same place. Just choose the lowest numbers they could be)
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Physical properties: ALCOHOLS

  • All contain a Hydroxyl (OH) group
  • The longer the molecule, the higher the melting/boiling point (more possible attractions between molecules)
  • Even the simplest alcohols are liquid at room temperature, as OH groups facilitate Hydrogen bonding between molecules. Thus, Alkanes/enes of the same chain length have far lower melting/boiling points.
  • Again because of Hydrogen bonding, alcohols mix freely with water
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Physical properties: CARBOXYLIC ACIDS

  • All contain a Carboxyl group ( C=O, O--H) 
  • Melting/boiling points governed by chain length. The longer the chain the higher the melting/boiling point.
  • The Carboxyl group forms two Hydrogen bonds with surrounding molecules. Because of this, the smaller carboxylic acid groups can dissolve in water. The longer the chain gets, however, the less soluble it becomes. (less hygrogen bonds forming in a given volume, as longer molecules take up more space)
  • Extremely high melting/boiling points
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