IB›IB Chemistry HL›Mind mapsS2.2 The covalent modelIB Chemistry HL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsCovalent bondsShared pair attracted to both nucleiOctet rule: valence shell of 8 electronsMore shared pairs: shorter, stronger bondCoordination bond: both electrons from one atomExamples: NHX4X+\ce{NH4+}NHX4X+, HX3OX+\ce{H3O+}HX3OX+, COVSEPR shapes2 domains: linear 180°3 domains: trigonal planar 120°4 domains: tetrahedral 109.5°1 lone pair: trigonal pyramidal ~107°2 lone pairs: bent ~105°Symmetrical molecules have no net dipoleExpanded octetsPeriod 3 onwards can exceed 8 electrons5 domains: trigonal bipyramidal; seesaw (SF₄)3 bonds + 2 lone pairs: T-shaped6 domains: octahedral; square planar (XeF₄)Lone pairs sit equatorial in 5 domainsCovalent modelbonding and shapesσπsp³Formal charge, resonanceFC=V−non-bonding−12bondingFC = V - \text{non-bonding} - \tfrac{1}{2}\text{bonding}FC=V−non-bonding−21bondingPrefer FC closest to zeroNegative charge on most electronegative atomResonance hybrid is the real structureBenzene: all C–C bonds 0.140 nmBenzene about 152 kJ mol⁻¹ more stableσ, π, hybridisationσ: head-on overlap, along bond axisπ: sideways overlap, above and below axisDouble bond = 1σ + 1π; triple = 1σ + 2πsp³: 4 domains, tetrahedralsp²: 3 domains, 120°, one p for πsp: 2 domains, linear, two p for πExam tipsCount domains first, then name the shapeResonance forms do not switch back and forthEach bond has only one σ bondEvaluate a model using its limits