• 54 questions

AP Chemistry Atomic Structure and Periodicity Practice Test

Unofficial multiple-choice practice for Unit 1 of AP Chemistry: electron configuration, photoelectron spectra, periodic trends and the mole.

A neutral atom has 14 electrons. Which configuration is its ground state?

Pick an answer, then press Check answer. Then you see Correct or Not quite, with the reason. Keys: A to D pick, Enter checks.

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Unofficial practice questions, not affiliated with the College Board. Bank checked October 9, 2026.

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All 54 questions

Topic 1.1: Moles and molar mass 6

  • A copper wire has a mass of 12.7 g. Copper's molar mass is 63.55 g/mol. How many copper atoms are in the wire? Purdue University, General Chemistry Topic Review, "Stoichiometry"; PubChem periodic table, National Library of Medicine; course topic 1.1
  • A sample of methane, CH₄, contains 2.41 × 10²⁴ hydrogen atoms. How many moles of methane are in the sample? NIST, CODATA value of the Avogadro constant; course topic 1.1
  • The average mass of one atom of an element is 26.98 amu. What is the mass of one mole of atoms of that element? Purdue University, General Chemistry Topic Review, "Stoichiometry"; PubChem periodic table, National Library of Medicine; course topic 1.1
  • How many atoms of oxygen does a 0.500 mol sample of CO₂ contain? NIST, CODATA value of the Avogadro constant; course topic 1.1
  • What is the mass of 3.00 mol of water, H₂O (molar mass 18.02 g/mol)? Purdue University, General Chemistry Topic Review, "Stoichiometry"; PubChem periodic table, National Library of Medicine; course topic 1.1
  • Which sample contains the greatest number of atoms? Purdue University, General Chemistry Topic Review, "Stoichiometry"; PubChem periodic table, National Library of Medicine; course topic 1.1
Show all 54 questions (48 more)

Topic 1.2: Mass spectra of elements 5

  • Boron has two isotopes, boron-10 and boron-11, and an atomic weight of 10.81. What does the atomic weight show about the two isotopes? NIST, Atomic Weights and Isotopic Compositions, boron; PubChem periodic table, National Library of Medicine; course topic 1.2
  • The mass spectrum of an element shows two peaks of almost equal height, at 79 amu and 81 amu. Which element is it? NIST, Atomic Weights and Isotopic Compositions, bromine; PubChem periodic table, National Library of Medicine; course topic 1.2
  • The mass spectrum of chlorine atoms shows two peaks: 34.97 amu at 75.76% abundance and 36.97 amu at 24.24%. What average atomic mass do these give? NIST, Atomic Weights and Isotopic Compositions, chlorine; Purdue University, General Chemistry Topic Review, "Stoichiometry"; course topic 1.2
  • The mass spectrum of magnesium has peaks at 24, 25 and 26 amu, and the peak at 24 is by far the tallest. What does that show? NIST, Atomic Weights and Isotopic Compositions, magnesium; Wikipedia, "Mass spectrometry"; course topic 1.2
  • What is plotted along the horizontal axis of the mass spectrum of an element? Wikipedia, "Mass spectrometry" and "Mass spectrum"; course topic 1.2

Topic 1.3: Elemental composition of pure substances 6

  • A 7.15 g sample of an oxide of copper holds 6.35 g of copper (63.55 g/mol) and 0.80 g of oxygen (16.00 g/mol). What is its empirical formula? Wikipedia, "Empirical formula"; PubChem periodic table, National Library of Medicine; course topic 1.3
  • A compound has the empirical formula CH₂ and a molar mass of about 56 g/mol (C 12.01, H 1.008 g/mol). What is its molecular formula? Wikipedia, "Empirical formula"; PubChem periodic table, National Library of Medicine; course topic 1.3
  • A compound is 40.0% calcium, 12.0% carbon and 48.0% oxygen by mass (Ca 40.08, C 12.01, O 16.00 g/mol). What is its empirical formula? Wikipedia, "Empirical formula"; PubChem periodic table, National Library of Medicine; course topic 1.3
  • Glucose has the molecular formula C₆H₁₂O₆. What is its empirical formula? Wikipedia, "Empirical formula"; course topic 1.3
  • One sample of pure water comes from a glacier and another is made in a laboratory. How do their oxygen-to-hydrogen mass ratios compare? Wikipedia, "Law of definite proportions"; course topic 1.3
  • What is the percent by mass of nitrogen in ammonia, NH₃ (N 14.01 g/mol, H 1.008 g/mol)? Purdue University, General Chemistry Topic Review, "Stoichiometry"; PubChem periodic table, National Library of Medicine; course topic 1.3

Topic 1.4: Composition of mixtures 4

  • A 10.00 g mixture of sodium chloride and sand contains 2.43 g of chlorine. Sand holds no chlorine, and NaCl is 60.66% chlorine by mass. What mass of NaCl is in the mixture? PubChem periodic table, National Library of Medicine; Wikipedia, "Mixture"; course topic 1.4
  • A brass sample contains only copper and zinc. Its mass is 8.00 g, of which 5.60 g is copper. What is the percent by mass of zinc? Wikipedia, "Mixture"; course topic 1.4
  • Pure calcium carbonate, CaCO₃, is 40.0% calcium by mass. Analysis of a powder sold as calcium carbonate finds 36.0% calcium. What is the best conclusion? Wikipedia, "Law of definite proportions" and "Elemental analysis"; PubChem periodic table, National Library of Medicine; course topic 1.4
  • Which statement is true of a mixture but not of a pure compound? Wikipedia, "Mixture"; course topic 1.4

Topic 1.5: Atomic structure and electron configuration 9

  • A hydrogen atom and a He⁺ ion each have one electron. At the same distance from the nucleus, how does the attraction on the electron in He⁺ compare with that in hydrogen? Wikipedia, "Coulomb's law"; Purdue University, General Chemistry Topic Review, "Ionization Energy and Electron Affinity"; course topic 1.5
  • A neutral atom has 14 electrons. Which configuration is its ground state? Wikipedia, "Aufbau principle"; PubChem periodic table, National Library of Medicine; course topic 1.5
  • A sulfur atom is 1s² 2s² 2p⁶ 3s² 3p⁴. How many valence electrons does it have? Wikipedia, "Valence electron" and "Core electron"; course topic 1.5
  • An electron and a proton start a distance r apart and are moved to 2r apart. By Coulomb's law, what happens to the force between them? Wikipedia, "Coulomb's law"; course topic 1.5
  • An iron atom is [Ar] 4s² 3d⁶. What is the ground-state configuration of the Fe²⁺ ion? Wikipedia, "Electron configuration"; PubChem periodic table, National Library of Medicine; course topic 1.5
  • Calcium ends at 4s². Into which subshell does the next element, scandium, put its added electron? Wikipedia, "Aufbau principle"; PubChem periodic table, National Library of Medicine; course topic 1.5
  • In a sodium atom, why does it take far more energy to remove a 1s electron than the 3s electron? Wikipedia, "Shielding effect" and "Coulomb's law"; course topic 1.5
  • What is the ground-state electron configuration of the oxide ion, O²⁻? Purdue University, General Chemistry Topic Review, "The Size of Atoms"; PubChem periodic table, National Library of Medicine; course topic 1.5
  • Which ion has the same electron configuration as an argon atom? PubChem periodic table, National Library of Medicine; Purdue University, General Chemistry Topic Review, "Atoms and Ions"; course topic 1.5

Topic 1.6: Photoelectron spectroscopy 7

  • The 1s peak of fluorine lies at a far higher binding energy than the 1s peak of lithium. Why? Wikipedia, "Coulomb's law"; Purdue University, General Chemistry Topic Review, "The Size of Atoms"; course topic 1.6
  • A photoelectron spectrum has three peaks. From highest to lowest binding energy, their relative heights are 2, 2 and 1. Which element is it? PubChem periodic table, National Library of Medicine; College Board, AP Chemistry Course and Exam Description, course topic 1.6
  • A photoelectron spectrum shows six peaks. From highest to lowest binding energy, their relative heights are 2, 2, 6, 2, 6 and 1. Which element is it? PubChem periodic table, National Library of Medicine; College Board, AP Chemistry Course and Exam Description, course topic 1.6
  • How many peaks would the photoelectron spectrum of magnesium, 1s² 2s² 2p⁶ 3s², show? PubChem periodic table, National Library of Medicine; College Board, AP Chemistry Course and Exam Description, course topic 1.6
  • In a photoelectron spectrum, what does the position of a peak along the energy axis show? Wikipedia, "Photoemission spectroscopy"; College Board, AP Chemistry Course and Exam Description, course topic 1.6
  • In the photoelectron spectrum of neon, 1s² 2s² 2p⁶, how does the height of the 2p peak compare with the height of the 2s peak? PubChem periodic table, National Library of Medicine; College Board, AP Chemistry Course and Exam Description, course topic 1.6
  • Which peak in the photoelectron spectrum of aluminum, 1s² 2s² 2p⁶ 3s² 3p¹, has the lowest binding energy? Purdue University, General Chemistry Topic Review, "Ionization Energy and Electron Affinity"; College Board, AP Chemistry Course and Exam Description, course topic 1.6

Topic 1.7: Periodic trends 12

  • An element's first three ionization energies rise step by step, and its fourth is many times larger than its third. In which group is the element most likely found? Purdue University, General Chemistry Topic Review, "Ionization Energy and Electron Affinity"; course topic 1.7
  • Boron's first ionization energy (8.30 eV) is lower than beryllium's (9.32 eV), against the general trend across a period. Why? Purdue University, General Chemistry Topic Review, "Ionization Energy and Electron Affinity"; PubChem periodic table, National Library of Medicine; course topic 1.7
  • Going down group 17 from fluorine to iodine, why do the atoms get larger? Purdue University, General Chemistry Topic Review, "The Size of Atoms"; course topic 1.7
  • How does a chloride ion, Cl⁻, compare in size with a neutral chlorine atom? Purdue University, General Chemistry Topic Review, "The Size of Atoms"; course topic 1.7
  • Na⁺, Mg²⁺ and Al³⁺ each have 10 electrons. Which is the smallest? Purdue University, General Chemistry Topic Review, "The Size of Atoms"; course topic 1.7
  • Oxygen's first ionization energy (13.62 eV) is slightly lower than nitrogen's (14.53 eV). Which fact explains it? Purdue University, General Chemistry Topic Review, "Ionization Energy and Electron Affinity"; PubChem periodic table, National Library of Medicine; course topic 1.7
  • Sodium's first ionization energy is 5.14 eV and rubidium's is 4.18 eV. Potassium lies between them in group 1. Which value is the best estimate for potassium? Purdue University, General Chemistry Topic Review, "Ionization Energy and Electron Affinity"; PubChem periodic table, National Library of Medicine; course topic 1.7
  • What does the electron affinity of chlorine measure? Purdue University, General Chemistry Topic Review, "Ionization Energy and Electron Affinity"; course topic 1.7
  • Which list is in order of increasing electronegativity? Wikipedia, "Electronegativity"; PubChem periodic table, National Library of Medicine; course topic 1.7
  • Which list puts the atoms in order of increasing atomic radius? Purdue University, General Chemistry Topic Review, "The Size of Atoms"; course topic 1.7
  • Why does a valence electron in a many-electron atom feel less than the full charge of the nucleus? Wikipedia, "Effective nuclear charge" and "Shielding effect"; course topic 1.7
  • Why does first ionization energy generally rise from left to right across a period? Purdue University, General Chemistry Topic Review, "Ionization Energy and Electron Affinity"; course topic 1.7

Topic 1.8: Valence electrons and ionic compounds 5

  • Aluminum has three valence electrons and sulfur has six. What is the formula of the ionic compound aluminum sulfide? PubChem periodic table, National Library of Medicine; Purdue University, General Chemistry Topic Review, "Atoms and Ions"; course topic 1.8
  • Calcium forms the chloride CaCl₂. Strontium lies directly below calcium in group 2. What formula would you predict for strontium chloride? PubChem periodic table, National Library of Medicine; Wikipedia, "Valence electron"; course topic 1.8
  • Selenium is in group 16, below oxygen and sulfur. Which ion would it be expected to form in an ionic compound? PubChem periodic table, National Library of Medicine; Purdue University, General Chemistry Topic Review, "Atoms and Ions"; course topic 1.8
  • Sodium and potassium each react with chlorine to give a compound of formula MCl. Which feature of the two metal atoms explains the matching formulas? PubChem periodic table, National Library of Medicine; Wikipedia, "Valence electron"; course topic 1.8
  • Why does sodium form Na⁺ in its compounds and never Na²⁺? Purdue University, General Chemistry Topic Review, "Ionization Energy and Electron Affinity"; course topic 1.8

How this list was compiled: Our own questions, written to Unit 1 (Atomic Structure and Properties) of the College Board's AP Chemistry Course and Exam Description, effective fall 2024, https://apcentral.collegeboard.org/media/pdf/ap-chemistry-course-and-exam-description.pdf, read 2026-10-09. Each fact was read on 2026-10-09 in the public page named under its question: the General Chemistry Topic Review of Purdue University, the PubChem periodic table of the National Library of Medicine, the atomic data pages of NIST, and Wikipedia. Every calculated answer was worked a second time from the numbers in the question. Licence: Own work. Short quotations from the public documents named under each question.

How it works

This AP Chemistry atomic structure and periodicity practice test has 54 questions of our own on Unit 1, Atomic Structure and Properties. It is unofficial and not affiliated with or endorsed by the College Board, which owns AP.

Read the full guide

What Unit 1 covers

The College Board's course description, read October 9, 2026, gives Unit 1 eight topics. The bank opens on the four the search names: electron configuration (9 questions), photoelectron spectroscopy (7), periodic trends (12) and valence electrons and ionic compounds (5). Then come moles and molar mass (6), mass spectra (5), composition of pure substances (6) and of mixtures (4). The description gives the topics no weights, so the spread is ours.

Sources you can open

Each answer names the page it was checked on: a Purdue University chemistry review, the PubChem periodic table, a NIST data page or a Wikipedia article. Molar masses are printed in the questions.

  • Explain every trend with Coulomb's law: more protons pull harder, and more shells put the outer electrons farther out, behind more shielding.
  • Read a photoelectron spectrum from the high-energy side. The first peak is 1s, and each height counts the electrons in one subshell.

Questions and answers

What is Unit 1 in AP Chemistry?

Atomic Structure and Properties, the first of nine units. The course description allows about 9 to 10 class periods for it. Periodicity, the repeating pattern of properties across the periodic table, is its topic 1.7.

How much of the AP Chemistry exam is Unit 1?

Between 7 and 9% of the multiple-choice section, by the College Board's course page. That section has 60 questions in 1 hour 30 minutes and counts for half of the exam score.

Do you get a periodic table on the AP Chemistry exam?

Yes. The course description says students get a periodic table and a formula sheet. Keep a periodic table beside you for the trend questions here.

Does the AP Chemistry exam ask for quantum numbers?

No. The course description says assigning quantum numbers to electrons will not be assessed, and neither will writing the configurations of elements that break the Aufbau principle. No question here asks for either.

Are these real AP Chemistry exam questions?

No. Real exam questions belong to the College Board, and none is used or reworded here. Each question was written for this page from the Unit 1 topic list and a public source.

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