Properties of Alkanes
- Alkanes are saturated (only contain single bonds) hydrocarbons (only contain hydrogen and carbon)
- The single bonds in Alkanes are σ bonds.
- σ bonds can rotate freely
- σ bonds are the overlap of orbitals directly between the two nuclei.
- Alkanes form a tetrahedral shape around the carbon atoms.
- 4 bonding pairs, 0 lone pairs.
- Electron pairs repel each other and thus have to be as far and equally spaced around the carbon as possible.
- Bond angle of 109.5 degrees.
- As the chain length of an alkane increases, so does the boiling point.
- The more electrons you have, and the more distance over which they can move, the bigger the possible temporary dipoles and therefore the bigger the london dispersion forces.
- As branching of an alkane increases, the boiling point deceases.
- Long thin molecules lie closer together and have more surface contact, making dispersion forces stronger.
- Alkanes are relatively unreactive.
- σ bonds have low polarity and high enthalpy
- the C-C and C-H bonds require a lot of energy to break.
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Combustion of Alkanes
- The more carbon atoms in the Alkane, the more energy released. But the more oxygen needed.
- Complete Combustion
- Products are CO2 and H2O
- Incomplete Combustion
- Products are CO/C and H2O.
- Happens when there is a lack of oxygen.
- CO is deadly as it binds with the blood in place of Oxygen.
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- Conditions: Presence of UV Light to break the CL2.
- Initiation - Cl2 -> 2*CL
- Propagation - *Cl + CH4 -> *CH3 + HCl
*CH3 + Cl2 -> CH3CL + *Cl
- Termination - 2*Cl -> Cl2
2*CH3 -> C2H6
- Termination is when 2 radicals react together.
- Mixture of Organic Products due to further substitution and termination.
- Mixture of structural isomers.
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