IGCSE›Oxford AQA IGCSE Chemistry›Mind mapsHydrocarbonsOxford AQA IGCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsWhat are they?Molecules of hydrogen and carbon atoms onlyCrude oil is a mixture of many hydrocarbonsMost belong to the alkanesAlkanesSaturated: every C-C bond is singleGeneral formula CXnHX2n+2\ce{C_nH_{2n+2}}CXnHX2n+2Each carbon forms four single bondsFirst threeMethane CHX4\ce{CH4}CHX4, one carbonEthane CX2HX6\ce{C2H6}CX2HX6, two carbonsPropane CX3HX8\ce{C3H8}CX3HX8, three carbonsShown as molecular, displayed or structural formulaeHydrocarbonshydrogen and carbon onlyCH4C2H6C3H8Size trendsBigger molecule: boiling point increasesBigger molecule: viscosity increasesBigger molecule: flammability decreasesLonger chains tangle moreSeparating themFractional distillation splits crude oil into fractionsShort chains collect near the topLong chains collect near the bottomExam tipsCheck formula: propane n=3n=3n=3, so H=2(3)+2=8\ce{H}=2(3)+2=8H=2(3)+2=8Intermolecular forces increase, not covalent bond strength