IGCSE›Cambridge IGCSE Physics›Mind mapsThe AtomCambridge IGCSE Physics: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsStructureTiny dense nucleus at the centreElectrons orbit in shellsNucleus holds protons and neutronsMost of the atom is empty spaceNucleus holds nearly all the massHolding togetherPositive nucleus attracts negative electronsElectrostatic attraction holds the atom togetherElectrons have negligible massIonsLose electrons → positive ion (cation)Gain electrons → negative ion (anion)Only electrons move, nucleus unchangedMg→MgX2++2 eX−\ce{Mg -> Mg^2+ + 2e-}MgMgX2++2eX− leaves 12 protons, 10 electronsThe atomstructure and evidencep⁺ne⁻Rutherford's testAlpha particles fired at thin gold foilMost pass straight through → mostly empty spaceSome deflected at large anglesA few bounce backwardsConclusionsSmall, dense, positive nucleusAlpha particles repelled by the nucleusNucleus diameter about 10,000× smaller than atomReplaced the plum pudding modelExam tipsLink each observation to its conclusionMention small size and high density of nucleus