Hydrocarbons

A hydrocarbon is a compound that contains hydrogen and carbon atoms only.Each carbon atom forms four covalent bonds, so carbon atoms can bond to each other to make chains and rings of almost any length, with hydrogen atoms bonded to the remaining positions. This is why there are so many organic compounds.The simplest hydrocarbon is methane, CH₄. Other examples are ethane, C₂H₆, propane, C₃H₈, and ethene, C₂H₄.Hydrocarbons are sorted into families. Alkanes contain only carbon-carbon single bonds, alkenes contain at least one C=C double bond, and arenes, such as benzene, contain a ring with delocalised electrons.Compounds such as ethanol, C₂H₅OH, and chloromethane, CH₃Cl, are not hydrocarbons, because they contain atoms of other elements (oxygen and chlorine). They are made from hydrocarbons, so they are often called hydrocarbon derivatives.Crude oil and natural gas are the main sources of hydrocarbons. They are used as fuels and as the starting materials for plastics, solvents and many other chemicals.The C-H and C-C bonds in hydrocarbons are almost non-polar, so hydrocarbons do not mix with water: they are insoluble and form a separate layer. The only forces between hydrocarbon molecules are London forces. Longer molecules have more electrons and more points of contact, so the London forces get stronger and the boiling point rises as the chain length increases. Methane to butane are gases at room temperature, while longer chains are liquids and then waxy solids.