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Structure 2. Models of bonding and structure

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  1. 2.1 The ionic model

    1. • Metal atoms lose electrons → cations (+) • Non-metal atoms gain electrons → anions (−) • Predict ion charges from electron configurations

    2. • Electrostatic attraction between oppositely charged ions • Binary ionic compounds: cation first, anion with "-ide" suffix • Deduce formulas and names of ionic compounds, including common polyatomic ions

    3. • 3D lattice structures, empirical formulas • Properties: volatility, electrical conductivity, solubility • Explain properties using lattice structure and ion mobility

  2. 2.2 The covalent model

    1. 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)

    2. 2.2.2Bond types and strength

      • Single, double, triple bonds (1, 2, 3 shared pairs) • More bonds → shorter length, stronger bond

    3. 2.2.3Coordination bonds

      • Both electrons from same atom • Identify coordination bonds; include transition element complexes at HL

    4. 2.2.4VSEPR 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 shapes

    5. 2.2.5Bond polarity

      • Results from electronegativity differences • Deduce polar bonds from electronegativity values and show bond dipoles

    6. 2.2.6Molecular polarity

      • Depends on bond polarity + molecular geometry • Net dipole moment • Identify when bond dipoles cancel or produce a polar molecule/ion

    7. 2.2.7Covalent network structures

      • Carbon allotropes: diamond, graphite, fullerenes, graphene • Silicon and silicon dioxide

    8. 2.2.8Intermolecular forces (IMF)

      • London dispersion forces • Dipole-induced dipole • Dipole-dipole • Hydrogen bonding • Deduce IMF types from molecular size and polarity

    9. 2.2.9IMF 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 mass

    10. 2.2.10Chromatography

      • Separates components based on IMF attractions • Calculate and interpret RF values • Link mobile/stationary phase attraction to separation; operational details are not assessed

    11. 2.2.11(HL)—Resonance structures

      • Multiple possible positions for double bonds • Deduce resonance structures and use the term delocalization

    12. 2.2.12(HL)—Benzene (C₆H₆)

      • Important resonance example

    13. 2.2.13(HL)—Expanded octets

      • Atoms with 5 or 6 electron domains • VSEPR for these species • Draw Lewis formulas and geometries for five- and six-domain species

    14. 2.2.14(HL)—Formal charge

      • Determine preferred Lewis formula • Use formal charge to compare valid Lewis structures

    15. 2.2.15(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 sides

    16. 2.2.16(HL)—Hybridization

      • Mixing atomic orbitals to form hybrid orbitals • Relationships: Lewis formulas → electron domains → geometry → hybridization • Analyse hybridization and bond formation in molecules and ions

  3. 2.3 The metallic model

    1. • Electrostatic attraction between cation lattice and delocalized electrons • Properties: electrical/thermal conductivity, malleability

    2. • Depends on ion charge and metal ion radius • Trends in melting points (s and p block metals)

    3. • Delocalized d-electrons • High melting points, electrical conductivity

  4. 2.4 From models to materials

    1. • Ionic ↔ covalent ↔ metallic • Bonding triangle representation

    2. • Position determined by relative contributions of three bonding types • Predict properties from position • Use electronegativity data to place compounds in the bonding triangle

    3. • Mixtures of metals with enhanced properties • Non-directional bonding

    4. • Macromolecules from repeating monomers • Properties of plastics

    5. • Form by breaking double bonds in monomers • Represent repeating units from given alkene monomers

    6. • Form with release of small molecule • Polyamides and polyesters • Represent repeating units from given difunctional monomers