How atoms combine. Ionic, covalent, and metallic bonding, Lewis diagrams, resonance and formal charge, and the VSEPR model that predicts molecular geometry and hybridization.
Seven topics from the College Board CED, in order.
Topic 2.1
Types of Chemical Bonds
Ionic, covalent, and metallic bonding, and how electronegativity difference predicts bond type.
Topic 2.2
Intramolecular Force & Potential Energy
The relationship between bond length, bond energy, and potential energy curves.
Topic 2.3
Structure of Ionic Solids
Crystal lattice structure, coordination number, and how lattice energy relates to ionic charge and radius.
Topic 2.4
Structure of Metals & Alloys
The electron sea model explains malleability, ductility, and conductivity; alloys modify these properties.
Topic 2.5
Lewis Diagrams
Drawing structures that satisfy the octet rule, including single, double, and triple bonds and lone pairs.
Topic 2.6
Resonance & Formal Charge
Using formal charge to evaluate Lewis structures and represent delocalized electrons with resonance.
Topic 2.7
VSEPR & Bond Hybridization
Predicting electron-domain and molecular geometry, and connecting hybridization to sigma and pi bonds.
About Unit 2
Unit 2 builds directly on Unit 1's atomic structure to explain how atoms combine into compounds. You'll learn the three major bonding types — ionic, covalent, and metallic — and how the difference in electronegativity between atoms predicts which type forms. From there, you'll learn to draw Lewis structures, evaluate them with formal charge, represent delocalized electrons with resonance, and use the VSEPR model to predict 3D molecular shape and orbital hybridization.
This unit is roughly 7–9% of the AP Chem exam and takes about 12–13 class periods. Like Unit 1, its modest exam weight undersells its importance — Unit 3 (intermolecular forces, the largest unit on the exam) depends entirely on correctly predicting molecular polarity and shape from this unit.
The College Board ties Unit 2 to the same core Big Ideas as Unit 1, applied at the molecular level:
Big Idea SAP
Structure & Properties — bond type and molecular shape determine compound behavior
Big Idea CE
Chemical Effects — Coulomb's law explains bond strength and lattice energy
Big Idea SPQ
Scale, Proportion & Quantity — formal charge quantifies how electrons are distributed in a structure