What you’ll learn16 learning objectivesChoose one objective for a focused lesson, or study the complete topic.2.2.1Covalent bonding• Electrostatic attraction between shared electron pair and nuclei• Octet rule: tendency to achieve 8 valence electrons• Lewis formulas (up to 4 electron pairs per atom)Syllabus objective2.2.2Bond types and strength• Single, double, triple bonds (1, 2, 3 shared pairs)• More bonds → shorter length, stronger bondSyllabus objective2.2.3Coordination bonds• Both electrons from same atom• Identify coordination bonds; include transition element complexes at HLSyllabus objective2.2.4VSEPR model• Predict molecular shapes from electron domain repulsion• Electron domain and molecular geometry (up to 4 domains)• Include bond angles and lone-pair effects for common shapesSyllabus objective2.2.5Bond polarity• Results from electronegativity differences• Deduce polar bonds from electronegativity values and show bond dipolesSyllabus objective2.2.6Molecular polarity• Depends on bond polarity + molecular geometry• Net dipole moment• Identify when bond dipoles cancel or produce a polar molecule/ionSyllabus objective2.2.7Covalent network structures• Carbon allotropes: diamond, graphite, fullerenes, graphene• Silicon and silicon dioxideSyllabus objective2.2.8Intermolecular forces (IMF)• London dispersion forces• Dipole-induced dipole• Dipole-dipole• Hydrogen bonding• Deduce IMF types from molecular size and polaritySyllabus objective2.2.9IMF strength and properties• Relative strength: London < dipole-dipole < hydrogen bonding• Effects on volatility, conductivity, solubility• Explain properties of covalent substances using IMF strength and molar massSyllabus objective2.2.10Chromatography• Separates components based on IMF attractions• Calculate and interpret RF values• Link mobile/stationary phase attraction to separation; operational details are not assessedSyllabus objective2.2.11(HL)—Resonance structures• Multiple possible positions for double bonds• Deduce resonance structures and use the term delocalizationSyllabus objective2.2.12(HL)—Benzene (C₆H₆)• Important resonance exampleSyllabus objective2.2.13(HL)—Expanded octets• Atoms with 5 or 6 electron domains• VSEPR for these species• Draw Lewis formulas and geometries for five- and six-domain speciesSyllabus objective2.2.14(HL)—Formal charge• Determine preferred Lewis formula• Use formal charge to compare valid Lewis structuresSyllabus objective2.2.15(HL)—Sigma (σ) and pi (π) bonds• σ bonds: head-on orbital combination, electron density along bond axis• π bonds: lateral p-orbital combination, electron density on opposite sidesSyllabus objective2.2.16(HL)—Hybridization• Mixing atomic orbitals to form hybrid orbitals• Relationships: Lewis formulas → electron domains → geometry → hybridization• Analyse hybridization and bond formation in molecules and ionsSyllabus objective