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Volume I · MMXXVI AP Chemistry
Library› AP Chemistry› Unit 1: Atomic Structure and Properties
⁂   AP Chemistry · Unit 1

1. Atomic Structure and Properties

7–9% of the AP exam. 7 key topics. 4 common errors analyzed.

7–9% exam weight

Unit 1: Atomic Structure and Properties

Unit 1 (Atomic Structure and Properties) is part of the AP Chemistry core curriculum. Work through each key topic in sequence, constructing ICE tables, net ionic equations, or energy diagrams as appropriate.

Key topics in this unit

  1. Moles and molar mass
  2. Mass spectra of elements
  3. Elemental composition of pure substances
  4. Atomic structure and electron configuration
  5. Photoelectron spectroscopy (PES)
  6. Periodic trends
  7. Valence electrons and ionic compounds

Common errors — what the rubric penalizes

These are the most frequently penalized mistakes on AP exam FRQs and MCQs. Review each before your next practice session.

Common error

Misreading mass spectra by mapping percent abundance to mass number instead of to relative peak height, producing incorrectly scaled isotope diagrams

Common error

Writing electron configurations that violate Hund's rule or the Aufbau principle, particularly for transition metals (e.g., Cr and Cu exceptions)

Common error

Confusing atomic radius trends: students often reverse the across-period trend, incorrectly expecting radius to increase left-to-right as more electrons are added

Common error

Conflating molar mass (g/mol) with atomic mass units (amu), leading to unit errors in multi-step stoichiometry problems

Study checklist

  • Can you list all key topics from memory without this page?
  • Have you worked through at least one FRQ-style question per topic?
  • Can you explain each common error above — and why the correct answer differs?
  • Have you reviewed the relevant College Board CED section and formula sheet entries?
Compound Structure and Properties →
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Our worked solutions and practice questions are original instructional content created by Tian2 AP. They are aligned to the concepts and skills described in College Board’s Course and Exam Description and are not reproductions of, or affiliated with, College Board’s official materials.