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Alkanes - Coggle Diagram
Alkanes
Basic information:
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All alkanes contain only carbon and hydrogen, and thus all of them are hydrocarbons.
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Homologous series:
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For alkanes, the general formula is CnH2n+2, where n is the number of carbon atoms.
E.g. For methane n is 1, giving the formula CH4.
Under normal conditions molecules with up to four carbon atoms are gases, those with between five and 16 carbon atoms are liquids, while those with more than 16 carbon atoms are solids.
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Structural isomerism:
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Branched isomers have lower boiling points, because the branches make it harder for the molecules to get close. So the attraction between them is less strong, and less heat is needed to overcome it.
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Chemical properties:
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Generally, the alkanes are quite unreactive. They are generally not affected by alkalis, acids or many other substances.
But alkanes do burn well in a good supply of oxygen, forming carbon dioxide and water vapour, and giving out plenty of heat. So they are used as fuels. Methane burns the most easily.
If there is not enough oxygen, the alkanes undergo incomplete combustion, giving poisonous carbon monoxide.
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