Unit 2: Compound Structure and Properties
Practice AP Chemistry Unit 2 — Lewis structures, VSEPR, molecular geometry, hybridization, and bond polarity. AP-style MCQ and FRQ questions included.
What Unit 2 Covers in AP Chemistry
Unit 2 moves from individual atoms to the bonds and geometries that form when atoms combine. AP-style questions here test your ability to draw and interpret molecular structure, predict geometry, and connect bonding models to observed properties.
Core Topics in Unit 2
- Lewis structures — Drawing complete Lewis structures including formal charges, expanded octets for third-period and beyond elements, and choosing the most stable resonance form
- VSEPR theory — Predicting electron geometry and molecular geometry based on electron-pair repulsion, including the effect of lone pairs on bond angles
- Molecular geometry — Naming geometries (linear, bent, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral) and predicting bond angles
- Bond polarity and molecular polarity — Distinguishing polar bonds from polar molecules; understanding how symmetry affects net dipole moment
- Hybridization — Assigning sp, sp2, and sp3 hybridization and connecting hybridization to geometry and bond type
- Resonance — Drawing resonance structures, understanding delocalization, and applying resonance to bond length and strength comparisons
Key AP Skills for Structural Reasoning
AP Chemistry structural questions often present a molecule and ask you to do several things in sequence: draw the Lewis structure, identify geometry, assign hybridization, and determine polarity. Practise doing all four steps for the same molecule in one pass — this mirrors the multi-part FRQ format.
Common Pitfalls in Unit 2
- Forgetting lone pairs when determining molecular geometry — the shape name describes atom positions only, not electron pairs
- Assuming a molecule is polar simply because it contains polar bonds; symmetrical molecules like CO2 and CCl4 are nonpolar overall
- Confusing electron geometry with molecular geometry when lone pairs are present
- Incorrectly assigning formal charges, especially in molecules with multiple possible Lewis structures
Particulate-Level Reasoning
AP Chemistry frequently includes particulate diagrams — representations of molecules at the atomic level. In Unit 2, you may be asked to draw or interpret such diagrams to show bonding, lone pair placement, or the three-dimensional arrangement of atoms. Practise sketching 3D structures for common geometries, including trigonal bipyramidal and seesaw.