IB›IB Chemistry HL›Mind mapsS1.2 The nuclear atomIB Chemistry HL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsAtom structureSmall dense nucleus of protons and neutronsElectrons occupy the space around itA = mass number, Z = atomic numberProtons = Z; neutrons = A − ZElectrons = Z − ionic charge3479Se2−^{79}_{34}\text{Se}^{2-}3479Se2− has 34 p, 45 n, 36 eIsotopesSame element, different number of neutronsSame chemical properties, same electron arrangementDiffer in mass-dependent properties, e.g. densityRelative atomic massWeighted mean mass relative to 1/12 of C-12Ar=Σ(mass×abundance)100A_r = \frac{\Sigma(\text{mass} \times \text{abundance})}{100}Ar=100Σ(mass×abundance)Two isotopes: use fractions x and (1 − x)Neon peaks 20, 21, 22 give Ar=A_r =Ar= 20.19Nuclear atomisotopes and mass spectraAZm/zMass spectrometerMakes positive ions, separates by m/zPeak height gives relative abundance1+ ions: each peak is one isotopeNumber of peaks = number of isotopes2+ ions appear at half the mass, e.g. Mg at 12Cl₂⁺ peaks at 70, 72, 74 in ratio 9 : 6 : 1Isotope evidenceSame ArA_rAr can hide different abundancesIsotope ratios trace origin of lead or foodLimits: measurement uncertainty, sources testedExam tipsIgnore 2+ and molecular ion peaks when finding ArA_rArEvaluate: compare isotopes with numbersThen give at least one limitation