IB›IB Chemistry SL›Mind mapsS1.2 The nuclear atomIB Chemistry SL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsStructureTiny, dense, positive nucleusNucleus holds protons and neutronsElectrons orbit outside the nucleusMost of the atom is empty spaceAlmost all the mass is in the nucleusParticlesProton: mass 1, charge +1Neutron: mass 1, charge 0Electron: mass 0.0005, charge −1Nuclear symbolA = mass number (protons + neutrons)Z = atomic number (protons)Neutrons = A−ZA - ZA−ZElectrons = Z−Z -Z− charge1632S2−^{32}_{16}\text{S}^{2-}1632S2−: 16 p, 16 n, 18 eNuclear atomstructure and isotopespneZAX^{A}_{Z}\text{X}ZAXIsotopesSame protons, different neutronsSame chemical properties (same electrons)Different physical properties, e.g. densityExamples: 35Cl^{35}\text{Cl}35Cl and 37Cl^{37}\text{Cl}37ClRelative atomic massWeighted mean mass relative to 1/12 of C-12Ar=Σ(mass×%)100A_r = \frac{\Sigma(\text{mass} \times \%)}{100}Ar=100Σ(mass×%)Not a whole number: averages the isotopesTwo isotopes: use fractions xxx and (1−x)(1-x)(1−x)Exam tipsForming an ion changes only electronsAnswer lies between lightest and heaviest isotopeAnswer sits nearer the more abundant isotope