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S1.1 - Introduction to the particulate nature of matter S1.2 - The nuclear atom S1.3 - Electron configurations S1.4 - Counting particles by mass - The mole S1.5 - Ideal gases S2.1 - The ionic model S2.2 - The covalent model S2.3 - The metallic model S2.4 - From models to materials S3.1 - The periodic table - Classification of elements S3.2 - Functional groups - Classification of organic compounds R1.1 - Measuring enthalpy changes R1.2 - Energy cycles in reactions R1.3 - Energy from fuels R1.4 - Entropy and spontaneity AHL R2.1 - How much? The amount of chemical change R2.2 - How fast? The rate of chemical change R2.3 - How far? The extent of chemical change R3.1 - Proton transfer reactions R3.2 - Electron transfer reactions R3.3 - Electron sharing reactions R3.4 - Electron-pair sharing reactions

S2.2 - The covalent model

2.2.1 Covalent Bonds and Lewis Formulas 2.2.2 Bond Types 2.2.3 Co-coordination (Dative) Bonds 2.2.4 VSEPR Shapes of Molecules 2.2.5 Electronegativity and Bond Polarity 2.2.6 Polarity and Dipole Moments 2.2.7 Covalent Network Structures and Allotropes 2.2.8 Intermolecular Forces 2.2.9 Physical Properties of Covalent Substances 2.2.10 Chromatography and Intermolecular Forces 2.2.11 Resonance Structures (AHL) 2.2.12 Benzene and Resonance (AHL) 2.2.13 Expanded Octet and VSEPR (AHL) 2.2.14 Formal Charge (AHL) 2.2.15 Sigma and Pi Bonds (AHL) 2.2.16 Hybridization (AHL)

Hybridization and Molecular Geometry HL Only

Specification Reference S2.2.16

Quick Notes

  • Hybridization = mixing atomic orbitals to form hybrid orbitals used in bonding.
  • Hybrid orbitals explain molecular geometry, bond strength, and bond angles.
  • The number of electron domains (bonding + lone pairs) around an atom determines the type of hybridization:
    • sp → 2 domains = linear (180°)
    • sp² → 3 domains = trigonal planar (120°)
    • sp³ → 4 domains = tetrahedral (109.5°)
  • Organic examples:
    • Ethyne (C≡C): sp
    • Ethene (C=C): sp²
    • Methane (CH₄): sp³
  • Inorganic examples:
    • BeCl₂: sp
    • BF₃: sp²
    • NH₃ or H₂O: sp³

Full Notes:

What Is Hybridization?

Hybridization is a model used to describe the process by which atomic orbitals (s, p) combine to form new hybrid orbitals for bonding.

These hybrid orbitals have equal energy and are oriented in specific geometries to minimise electron repulsion.

Hybridization explains the shapes predicted by VSEPR theory and observed experimentally.

You need to be comfortable with sp, sp2 and sp3 hybridization.

Determining Type of Hybridization

To determine hybridization:
Electron Domains Hybridization Geometry Bond Angle
2 sp Linear 180°
3 sp2 Trigonal planar 120°
4 sp3 Tetrahedral 109.5°

sp Hybridization (2 domains)

IB Chemistry diagram showing sp hybridization with two domains and linear geometry.

sp² Hybridization (3 domains)

IB Chemistry diagram showing sp² hybridization with three domains and trigonal planar geometry.

sp³ Hybridization (4 domains)

IB Chemistry diagram showing sp³ hybridization with four domains and tetrahedral geometry.

Hybridization of Carbon

Carbon is often used as an example for the forming of hybrid orbitals as it reacts.

IB Chemistry diagram showing carbon hybrid orbitals forming in hybridization.

Hybridisation can be used to explain why carbon atoms make four covalent bonds and the forming of double and triple bonds.

IB Chemistry diagram showing why carbon forms four covalent bonds due to hybridization.

Connecting Hybridization to Lewis Structures and Geometry

Molecule Lewis Features Hybridization Shape
CH4 4 single bonds sp3 Tetrahedral
H2O 2 bonds + 2 lone pairs sp3 Bent
CO2 2 double bonds sp Linear
BF3 3 bonds sp2 Trigonal planar
NH3 3 bonds + 1 lone pair sp3 Trigonal pyramidal
C2H4 C=C (1 π bond) sp2 Planar about C=C
C2H2 C≡C (2 π bonds) sp Linear

Summary