Ready to master atomic structure? Our free atomic structure quiz challenges chemistry atomic structure with atomic mass calculation questions, electron configuration practice, and periodic table quiz questions. Whether you're a student prepping for an atomic structure exam or a curious enthusiast exploring atomic structure practice, you'll test isotopic masses, valence electrons, and orbital assignments - all in a fun, interactive format. Want to sharpen your problem-solving? practice atomic calculations now, see where you stand, and boost your confidence - let's get started!
What does the atomic number of an element represent?
Number of protons in the nucleus
Total number of nucleons
Total number of electrons and neutrons
Number of neutrons in the nucleus
The atomic number is defined as the number of protons in the nucleus of an atom. It uniquely identifies an element and determines its position in the periodic table. Neutrons and electrons do not affect the atomic number. For more details, see Atomic Number on Wikipedia.
How many protons does a neutral carbon atom have?
6
12
7
8
Carbon has an atomic number of 6, which equals the number of protons in its nucleus. In a neutral atom, protons equal electrons. The neutron count can vary in isotopes but does not affect the proton number. See Carbon on Britannica for more.
Which subatomic particle has no electric charge?
Positron
Electron
Proton
Neutron
Neutrons are neutral particles found in the nucleus with no electric charge. Protons are positively charged and electrons are negatively charged. Positrons are the antimatter counterpart of electrons and carry a positive charge. Further reading: Neutron on Wikipedia.
How many electrons are present in a neutral helium atom?
3
4
2
1
Helium has an atomic number of 2, meaning it has two protons. In a neutral atom, the number of electrons equals the number of protons, so helium has two electrons. This configuration fills the 1s orbital. See Electron Configuration Review.
The average atomic mass of an element reflects which of the following?
The mass of its most abundant isotope
The weighted average mass of all naturally occurring isotopes
The total mass of protons and electrons only
The sum of its atomic number and neutron number
The atomic mass listed on the periodic table is a weighted average of all isotopic masses based on natural abundance. It accounts for each isotope's mass and relative frequency. It is not simply the most abundant isotope's mass or just protons plus electrons. For more information, see Standard Atomic Weight on Wikipedia.
Given chlorine has two common isotopes, Cl-35 (75% abundance) and Cl-37 (25%), what is its atomic mass?
36.0 u
72.0 u
35.5 u
35.0 u
Atomic mass = (35 × 0.75) + (37 × 0.25) = 26.25 + 9.25 = 35.5 u. This calculation uses percentage abundances as fractions and isotope masses. The average atomic mass reflects these weighted contributions. See Isotope Abundance Calculation.
In nuclide notation ¹??C, what does the superscript '14' represent?
Atomic number (protons only)
Number of electrons
Number of neutrons only
Mass number (total protons and neutrons)
The superscript is the mass number, which equals the sum of protons and neutrons in the nucleus. The subscript (6) is the atomic number (protons). Electrons are not shown in nuclide notation. For more, see Nuclear Notation on Wikipedia.
Which of these is true for a neutral atom?
Number of protons equals number of neutrons
Mass number equals atomic number
Number of protons equals number of electrons
Number of electrons equals number of neutrons
In a neutral atom, positive charges from protons balance negative charges from electrons, so their numbers are equal. Neutrons carry no charge, and mass number (protons + neutrons) is usually greater than atomic number. Read more: Introduction to the Atom.
Calculate the atomic mass of copper given Cu-63 (69.17%) and Cu-65 (30.83%).
64.00 u
63.00 u
63.55 u
63.70 u
Atomic mass = (63 × 0.6917) + (65 × 0.3083) ? 43.5821 + 20.0395 = 63.6216 u, commonly rounded to 63.55 u. This weighted average uses isotope masses and abundances. See Copper Isotopic Composition.
What is the electron configuration of neon (Ne)?
1s² 2s² 2p?
1s² 2p?
1s² 2s² 2p?
1s² 2s² 2p?
Neon has 10 electrons, filling the 1s orbital (2), then 2s (2), then 2p (6). This yields 1s²2s²2p?. It achieves a full octet in the second shell. More info at Electron Configuration on Wikipedia.
How many neutrons does an atom of ??Fe contain?
30
26
56
2
Iron-56 has a mass number of 56 and an atomic number of 26 (protons). Neutrons = 56 ? 26 = 30. This is standard for isotope calculations. See Mass Number and Nuclide Notation.
What is the mass defect of a nucleus?
Mass of electrons in the atom
Difference between the mass of separated nucleons and the mass of the nucleus
Mass of protons minus mass of neutrons
Mass lost during beta decay only
Mass defect is the mass difference between separate nucleons (protons + neutrons) and the assembled nucleus. This 'missing' mass is converted into binding energy that holds the nucleus together. Learn more at Mass Defect on Wikipedia.
Which element has the highest electronegativity?
Nitrogen
Chlorine
Oxygen
Fluorine
Fluorine has the highest electronegativity of all elements (3.98 on the Pauling scale) because of its small size and high effective nuclear charge. It strongly attracts bonding electrons. For periodic trends, see Electronegativity on Wikipedia.
How many electrons are present in an O²? ion?
12
6
10
8
A neutral oxygen atom has 8 electrons. The 2? charge indicates it has gained 2 more, so O²? has 10 electrons. Ion charges modify electron count, not protons. More at Ionic Bonding Review.
Calculate the atomic mass of magnesium given Mg-24 (78.99%), Mg-25 (10.00%), Mg-26 (11.01%).
25.32 u
24.00 u
24.32 u
25.00 u
Atomic mass = (24×0.7899)+(25×0.10)+(26×0.1101)=18.9576+2.5+2.8626?24.32 u. This weighted average uses each isotope's mass and abundance. See Periodic Table for isotopic data.
Which ion is formed when potassium loses one electron?
K²?
K?
K?
Ca?
A neutral potassium atom has 19 electrons. Losing one yields 18 electrons and a net +1 charge, forming K?. Losing more would form higher cations. Read more: Potassium on Wikipedia.
Calculate the nuclear binding energy in MeV for a nucleus with a mass defect of 0.20 u (1 u = 931.5 MeV).
186.3 MeV
931.5 MeV
184.0 MeV
46.6 MeV
Binding energy = mass defect × 931.5 MeV/u = 0.20 u × 931.5 MeV/u = 186.3 MeV. This energy is what holds the nucleus together. For calculation details, see Binding Energy on Wikipedia.
What is the correct alpha decay equation for uranium-238?
²³?U ? ²³?U + ?He
²³?U ? ²³?Pa + ?He
²³?U ? ²³?Th + ²He
²³?U ? ²³?Th + ?He
Alpha decay reduces the mass number by 4 and atomic number by 2. Uranium-238 (92 protons) emits an alpha particle (?He nucleus) to become thorium-234 (90 protons, 234 mass). More at Alpha Decay.
If element X has 20 protons, 12 neutrons, and 18 electrons, what is its net charge?
+18
+12
+2
-2
Protons (20) minus electrons (18) = +2 net charge. Neutrons are neutral and don't affect charge. This yields a divalent cation (X²?). See General Chemistry.
Which of the following best describes an isotope?
Atoms with the same number of electrons but different protons
Atoms with extra protons and electrons
Atoms of the same element with different numbers of neutrons
Atoms of different elements with the same mass number
Isotopes are atoms of the same element (same proton count) that differ in neutron numbers, thus different mass numbers. Their chemical behavior is similar but masses vary. For more, see Isotope on Wikipedia.
A radioactive isotope has a half-life of 5 days. How long until only 25% of the original sample remains?
10 days
20 days
15 days
5 days
25% remains after two half-lives (100% ? 50% ? 25%). One half-life is 5 days, so two half-lives equal 10 days. Each successive half-life halves the remaining quantity. See Half-life on Wikipedia.
The atomic mass of element Y is 10.7 u with isotopes Y-10 and Y-11. What is the percent abundance of Y-11?
50%
30%
70%
10%
Let x = fraction of Y-11. Then 10(1?x) + 11x = 10.7 ? 10 + x = 10.7 ? x = 0.7 or 70%. This weighted average matches the atomic mass. See Isotopic Abundance.
How many total orbitals are in the n = 3 electron shell?
18
6
27
9
For n=3, the subshells are 3s (1 orbital), 3p (3 orbitals), 3d (5 orbitals) totaling 1+3+5 = 9 orbitals. Each orbital can hold two electrons. See Atomic Orbital on Wikipedia.
Using E=mc², calculate the energy in joules for a mass defect of 0.004 u (1 u = 1.6605×10?²? kg, c = 3.00×10? m/s).
9.00×10?¹? J
5.98×10?¹³ J
1.00×10?¹² J
3.00×10?¹? J
Mass in kg = 0.004 × 1.6605×10?²? = 6.642×10?³? kg. E = mc² = 6.642×10?³? × (3.00×10?)² ? 5.98×10?¹³ J. This uses mass-energy equivalence. See Mass - Energy Equivalence.
In mass spectrometry, which principle explains why atomic masses are measured slightly less than the sum of proton and neutron masses?
Hund's rule
Mass-energy equivalence (mass defect)
Pauli exclusion principle
Heisenberg uncertainty principle
The mass defect arises because some mass converts to binding energy according to E=mc², making the nucleus lighter than separate nucleons. This mass - energy equivalence explains measured masses. For more, see Mass Defect.
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Study Outcomes
Calculate Atomic Masses -
Use weighted averages of isotopic abundances to accurately calculate the atomic mass of elements. Practice atomic mass calculation questions to build precision and confidence.
Determine Electron Configurations -
Write and interpret electron configurations for atoms and ions using established principles. Develop electron configuration practice skills for various elements.
Apply Periodic Table Principles -
Use periodic trends to predict element properties such as atomic radius, ionization energy, and electronegativity. Strengthen understanding through periodic table quiz questions.
Analyze Isotopic Composition -
Interpret isotopic notation and calculate relative abundances to explore atomic structure deeper. Reinforce knowledge through targeted atomic mass calculation questions.
Evaluate Subatomic Particle Roles -
Compare and contrast protons, neutrons, and electrons in defining atomic behavior. Enhance critical thinking with quiz-based scenarios on subatomic particles.
Master Quiz Strategies -
Develop effective approaches for tackling chemistry quiz questions on atomic structure confidently. Build test-taking skills to excel in quizzes and exams.
Cheat Sheet
Weighted Atomic Mass Calculation -
To calculate the atomic mass of an element, multiply each isotope's mass by its percent abundance (as a decimal) and sum the products following IUPAC guidelines. For example, chlorine's atomic mass = (35.45 amu × 0.7577) + (37.45 amu × 0.2423) ≈ 35.45 amu. Practice these atomic mass calculation questions to build confidence quickly!
Electron Configuration and Aufbau Principle -
The Aufbau principle dictates filling orbitals from lowest to highest energy (1s, 2s, 2p…), obeying Pauli exclusion and Hund's rule per University of California chemistry modules. Write configurations like O: 1s² 2s² 2p❴ to sharpen your electron configuration practice. Use the diagonal rule chart as a mnemonic to remember the filling order.
Periodic Table Trends -
Recognize that atomic radius decreases across a period and increases down a group, while ionization energy moves in the opposite direction according to NIST data. This pattern helps answer periodic table quiz questions about element reactivity and bonding tendencies. Visualizing these trends strengthens mastery of chemistry atomic structure concepts.
Isotope and Nuclide Notation -
Learn to represent isotopes as ¹³C for carbon-13 or in nuclide notation ₆¹³C to distinguish mass number (A) and atomic number (Z) as per IUPAC standards. Distinguishing isotopes is key to solving atomic mass calculation questions accurately. Remember the "A over Z" format: mass number on top, atomic number below.
Memorization Mnemonics for Subshells -
Use catchy phrases like "Some People Fear Dirty Earwax" for s, p, f, d subshell order from the American Chemical Society. Incorporate this trick during electron configuration practice and your atomic structure quiz. Mnemonics reduce stress and speed up recall in high-stakes chemistry atomic structure questions.
