College Board · AP Chemistry

AP Chemistry: Atomic Structure and Properties — Practice Questions & Answers

Moles, mass spectra, formulas, electron configuration, PES, and periodic trends that define how atoms behave.

868 practice questions available for this unit — here are 10 with full answers and explanations.

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Practice questions with answers

1 Multiple choice · Easy

How many moles of CO2 are present in 88.0 g of CO2? (Molar mass of CO2 = 44.0 g/mol)

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Whymoles = mass / molar mass = 88.0 g / 44.0 g/mol = 2.00 mol.
2 Multiple choice · Easy

Which subatomic particle has a positive charge and is found in the nucleus of an atom?

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WhyProtons carry a +1 charge and reside in the nucleus; neutrons are neutral and electrons are negative.
3 Multiple choice · Easy

How many valence electrons does a neutral atom of oxygen (group 16, period 2) have?

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WhyOxygen is in group 16 (6A), so it has 6 valence electrons in its outermost shell.
4 Multiple choice · Easy

Which of the following correctly describes a general periodic trend across a period from left to right?

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WhyAtomic radius decreases left to right because increasing nuclear charge pulls electrons in the same shell closer to the nucleus.
5 Multiple choice · Easy

What is the ground-state electron configuration of a neutral nitrogen atom (Z = 7)?

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WhyNitrogen has 7 electrons filling 1s, 2s, then 2p: 1s2 2s2 2p3.
6 Fill in the blank · Easy

A pure substance made of only one type of atom is called an . The number of protons in an atom is given by its number.

Answer: element, atomic

WhyAn element contains only one kind of atom, and the atomic number equals the number of protons.
7 Multiple choice · Medium

Chlorine has two stable isotopes: Cl-35 (mass 34.97, abundance 75.77%) and Cl-37 (mass 36.97, abundance 24.23%). Which value is closest to the average atomic mass of chlorine?

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WhyAverage = (0.7577)(34.97) + (0.2423)(36.97) = 26.50 + 8.96 = 35.45 amu.
8 Multiple choice · Medium

A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula? (C = 12.0, H = 1.0, O = 16.0 g/mol)

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WhyMoles: C 40.0/12.0 = 3.33, H 6.7/1.0 = 6.7, O 53.3/16.0 = 3.33; ratio 1:2:1 gives CH2O.
9 Multiple choice · Medium

In a photoelectron spectroscopy (PES) spectrum, what does a peak appearing at higher binding energy indicate about the electrons that produced it?

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WhyHigher binding energy means electrons are held more tightly, which corresponds to subshells closer to the nucleus (lower energy levels).
10 Multiple choice · Medium

Which neutral atom has the ground-state electron configuration 1s2 2s2 2p6 3s2 3p4?

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WhyCounting electrons gives 2+2+6+2+4 = 16, which is sulfur (Z = 16).

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Key terms in Atomic Structure and Properties

Atom: The smallest unit of an element that retains that element's chemical identity.
Element: A pure substance made of only one kind of atom, defined by its number of protons.
Proton: A positively charged subatomic particle found in the nucleus whose count sets the element's identity.
Neutron: An electrically neutral subatomic particle in the nucleus that contributes to atomic mass.
Electron: A negatively charged subatomic particle that occupies the region surrounding the nucleus.
Nucleus: The dense central core of an atom containing protons and neutrons.
Atomic Number: The count of protons in an atom's nucleus, symbolized Z.
Mass Number: The total count of protons plus neutrons in a particular atom, symbolized A.

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Practise other AP Chemistry units

Unit 2: Molecular and Ionic Compound Structure and Properties Unit 3: Intermolecular Forces and Properties Unit 4: Chemical Reactions Unit 5: Kinetics Unit 6: Thermodynamics Unit 7: Equilibrium Unit 8: Acids and Bases Unit 9: Applications of Thermodynamics