IGCSE›Cambridge IGCSE Chemistry›Mind mapsElements, Compounds and MixturesCambridge IGCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsThree typesElement: one type of atom onlyCompound: elements chemically combined, fixed proportionsMixture: substances not chemically combinedSeparatingMixtures: separate by physical methodsCompounds: only by a chemical reactionCompound properties differ from its elementsMixture keeps properties of its partsIron and sulfurMixed: still shows both, magnet separatesHeated: forms iron sulfide, a compoundNew substance, completely different propertiesElementscompounds and mixturesFeSFeSAtom structureDense nucleus: protons and neutronsElectrons in shells around nucleusProton +1, neutron 0, electron −1Overall neutral: protons = electronsAtomic numbersProton number = number of protonsMass number = protons + neutronsneutrons=A−Z\text{neutrons} = A - Zneutrons=A−ZSodium: 23 − 11 = 12 neutronsExam tipsShells hold 2, 8, 8Fill the innermost shell first