IB›IB Chemistry SL›Mind mapsS2.2 The covalent modelIB Chemistry SL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsCovalent bondShared pair attracts both nucleiOctet rule: 8 valence electrons (H: 2)More shared pairs: shorter, stronger bondLewis formulas show lone pairsCoordination: both electrons from one atomVSEPR shapesDomain = lone pair or any bond2 domains: linear 180°3 domains: trigonal planar 120°4 domains: tetrahedral 109.5°NHX3\ce{NH3}NHX3 pyramidal ~107°, HX2O\ce{H2O}HX2O bent ~105°Lone pairs repel morePolarityElectronegativity difference makes bonds polarMore electronegative atom gets δ−Dipoles that cancel: non-polar moleculeCOX2\ce{CO2}COX2, CHX4\ce{CH4}CHX4 non-polar; HX2O\ce{H2O}HX2O, NHX3\ce{NH3}NHX3 polarCovalent modelsharing electronsδ+δ−σπNetwork solidsDiamond: 4 bonds each, very hardGraphite: layers, delocalised electrons conductGraphene: one layer, strong conductorSilicon dioxide: hard, insulator, high m.p.Intermolecular forcesLondon in all molecules, grows with electronsDipole–dipole between polar moleculesHydrogen bond: H on N, O or FOrder: London < dipole–dipole < H-bondSimple molecules are volatile, non-conductingExam tipsDouble bond is one domainBoiling breaks intermolecular forces, not bondsRf=spot distancesolvent distanceR_f = \frac{\text{spot distance}}{\text{solvent distance}}Rf=solvent distancespot distance