Chem Alkanes Mindmap

ALKANES General Formula – CnH2n+2 Functional Group – No functional group. Only Single C-C bond Physical Properties – 1. Low mp and bp 2. Generally gases and liquids at r.t.p. 3. Colourless 4. Insoluble in water Trends – As C chain increases, 1. Mp and bp increases 2. Viscosity increases. 3. Flammability decreases. Alkanes are covalently bonded and exist as simple discrete molecules with weak intermolecular force of attraction. Very little energy is required to overcome the weak IMF thus resulting in low mp/bp. As the Mr of the molecule increases, the size of the molecule increase. With molecules having larger surface area, this results in stronger IMF between the molecules. More energy is required to overcome the IMF between the molecules. Therefore, mp and bp increases. As the C chain gets longer, the long molecules will get tangled. This increases the viscosity of the alkanes. As the C chain gets longer, the size of the molecules increases. The IMF of attraction increase. More energy required to overcome the IMF therefore flammability decreases. Alkanes are covalently bonded and exist as simple discrete molecules with weak intermolecular force of attraction. At room temperature, there is sufficient energy to overcome the weak IMF, resulting in the particles being far apart and in random arrangement thus gaseous state. Nomenclature – end with ane Prefix – No of C Suffix – Homologeous series Name Molecular Full Structural Formula Formula 1st member – Methane – CH4 2nd member – Ethane – C2H6 3rd member – Propane - C3H8 4th member – Butane – C4H10 5th member – Pentane – C5H12 Chemical Properties 1. Combustion a. Complete combustion – sufficient oxygen Products will be carbon dioxide and water. E.g – 2C2H6+ 5O2  4CO2 + 6H2O b. Incomplete combustion – insufficient oxygen Products will be carbon monoxide, soot (carbon) and water. 2. Substitution Condition – Gaseous halogen and UV light / diffuse sunlight CH4+ Cl2 (g)  CH3Cl+ HCl chloromethane + hydrogen chloride (white fumes) CH3Cl + Cl2(g)  CH2Cl2+ HCl dichloromethane + hydrogen chloride (white fumes) CH2Cl2 + Cl2(g)  CHCl3+ HCl trichloromethane + hydrogen chloride (white fumes) CHCl3 + Cl2(g)  CCl4+ HCl tetrachloromethane + hydrogen chloride (white fumes) Uses - Fuels