AP Chemistry / Topic
Atomic Structure and Properties
Unit 1 of AP Chemistry covers the composition of atoms, moles and molar mass, electron configuration, photoelectron spectroscopy, and the periodic trends that follow from Coulombic attraction. It is the foundation for bonding and reactivity arguments all year.
What the exam asks
- Convert among moles, mass, and particle counts using molar mass and Avogadro's number
- Interpret mass spectra of elements to find isotopic masses and abundances
- Write electron configurations and connect them to PES (photoelectron spectroscopy) spectra
- Explain periodic trends — atomic radius, ionization energy, electronegativity — using effective nuclear charge and shielding
- Use empirical and molecular formulas with percent composition
Key formulas and rules
n = mass / molar mass; N = n × 6.022×10²³
Σ(isotope mass × fractional abundance)
attraction ∝ (q1·q2)/r² — larger charge and smaller distance mean stronger attraction
across a period: radius ↓, ionization energy ↑; down a group: radius ↑, ionization energy ↓
a large jump between successive ionization energies marks a new (core) shell
Question bank breakdown
35
1
11 easy · 16 medium · 8 hard
Skills covered
Every question in the bank comes with a per-choice explanation, so you learn why each wrong answer is wrong — not just the key.
Sample question
From the free tier of the ScoreMint AP Chemistry bank — try it, then check the answer.
An atom of an element has 20 protons, 20 neutrons, and 18 electrons. Which of the following correctly identifies this species?
- A. Ca (neutral calcium atom)
- B. Ca²⁺ (calcium ion)
- C. Ar (neutral argon atom)
- D. K⁺ (potassium ion)
Show answer and explanation
Answer: B. Correct. The element is identified by its proton number (atomic number). 20 protons = calcium (Ca, Z = 20). It has 18 electrons, which is 2 fewer than its 20 protons, giving a charge of +2. Therefore this is Ca²⁺. The 20 neutrons give a mass number of 40 (the most common calcium isotope, Ca-40). ✓
Study tip
On the exam, every trend explanation must name Coulombic attraction: state what happens to nuclear charge and to electron distance/shielding. 'It's further right on the periodic table' earns no points by itself.