2.2 The covalent model

• 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)

• Single, double, triple bonds (1, 2, 3 shared pairs)

• More bonds → shorter length, stronger bond

• Both electrons from same atom

• Identify coordination bonds; include transition element complexes at HL

• 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

• Results from electronegativity differences

• Deduce polar bonds from electronegativity values and show bond dipoles

• Depends on bond polarity + molecular geometry

• Net dipole moment

• Identify when bond dipoles cancel or produce a polar molecule/ion

• Carbon allotropes: diamond, graphite, fullerenes, graphene

• Silicon and silicon dioxide

• London dispersion forces

• Dipole-induced dipole

• Dipole-dipole

• Hydrogen bonding

• Deduce IMF types from molecular size and polarity

• Relative strength: London < dipole-dipole < hydrogen bonding

• Effects on volatility, conductivity, solubility

• Explain properties of covalent substances using IMF strength and molar mass

• Separates components based on IMF attractions

• Calculate and interpret RF values

• Link mobile/stationary phase attraction to separation; operational details are not assessed