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Quizzes > Science

Which Element Has the Largest Atomic Radius?

Quick, free atomic radius quiz with instant results and explanations.

Editorial: Review CompletedCreated By: Betito HerreraUpdated Aug 25, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art atoms on sky blue quiz banner for free chemistry quiz testing atomic radius atomic number molecular structure

Use this quiz to identify the element with the largest atomic radius and understand how size changes across the periodic table. Get quick feedback on each question, then build confidence with periodic table practice and a deeper look at atomic size trends. Want something lighter? Explore periodic table trivia.

Which atom has the largest atomic radius among these elements?
Li
B
H
Be
Atomic radius increases down a group in the periodic table because electrons occupy higher energy levels further from the nucleus. Lithium (Li) is below hydrogen in Group 1, so it has a larger radius than H, Be, or B. This trend is due to increased electron shielding and a higher principal quantum number.
Which of these elements in the second period has the largest atomic radius?
Fluorine (F)
Nitrogen (N)
Carbon (C)
Oxygen (O)
Atomic radius decreases across a period from left to right because of increasing nuclear charge pulling electrons closer. Carbon is furthest to the left among these options in period 2, so it has the largest atomic radius.
Which element in the third period has the largest atomic radius?
Sodium (Na)
Silicon (Si)
Magnesium (Mg)
Aluminum (Al)
Moving left across a period decreases atomic radius because of stronger nuclear attraction. Sodium (Na) is the leftmost element in period 3 among these, so it has the largest radius.
Between potassium (K), calcium (Ca), scandium (Sc), and titanium (Ti), which has the largest atomic radius?
Scandium (Sc)
Potassium (K)
Titanium (Ti)
Calcium (Ca)
Atomic radius increases down a group and decreases across a period. Potassium is to the left of Ca, Sc, and Ti in period 4, so it has the largest radius.
Among the halogens F, Cl, Br, and I, which has the largest atomic radius?
Bromine (Br)
Iodine (I)
Chlorine (Cl)
Fluorine (F)
Atomic radius increases down a group because each element has an additional electron shell. Iodine is the heaviest of these halogens and lies lowest in Group 17, so it has the largest radius.
Which noble gas has the largest atomic radius?
Neon (Ne)
Argon (Ar)
Krypton (Kr)
Xenon (Xe)
In each group, atomic radius increases downwards due to additional electron shells. Xenon is the lowest of these noble gases (Group 18), so it has the largest radius.
Which ion has the largest ionic radius?
O²?
Mg²?
Al³?
Na?
Isoelectronic species with more negative charge have larger radii because extra electrons increase electron - electron repulsion and reduce effective nuclear attraction. O²? has the highest negative charge among these, so it is largest.
Which of these alkaline earth metals has the largest atomic radius?
Calcium (Ca)
Barium (Ba)
Radium (Ra)
Strontium (Sr)
Atomic radius generally increases down a group. Although radium is lower, relativistic effects and lack of reliable measured radii make barium typically cited as larger in standard tables. Ba is known to have a very large atomic radius among Group 2 elements.
Which of the following 4th-period elements has a larger atomic radius: Copper (Cu), Zinc (Zn), Gallium (Ga), or Germanium (Ge)?
Gallium (Ga)
Zinc (Zn)
Copper (Cu)
Germanium (Ge)
Atomic radius decreases across the period as nuclear charge increases. Gallium shows a slight increase compared to Zn and Cu due to poor shielding by filled 3d electrons, making its radius slightly larger.
Which element has a larger atomic radius: Selenium (Se) or Tellurium (Te)?
Selenium (Se)
Tellurium (Te)
Depends on allotrope
They are the same
Within a group, atomic radius increases downwards due to additional electron shells. Tellurium is one period below selenium in Group 16, so it has a larger radius.
Among the isoelectronic series N³?, O²?, F?, Na?, which species has the largest radius?
O²?
Na?
F?
N³?
Isoelectronic species have the same number of electrons, so more negative charge means less effective nuclear attraction per electron and a larger radius. N³?, having the highest negative charge, is largest.
Which lanthanide element has the largest atomic radius?
Cerium (Ce)
Praseodymium (Pr)
Lanthanum (La)
Neodymium (Nd)
Lanthanide contraction causes decreasing radius across the series due to poor shielding by 4f electrons. Lanthanum, being the first in the series, has the least contraction and thus the largest radius.
Which element has a larger atomic radius: Tungsten (W, Z=74) or Osmium (Os, Z=76)?
They have identical radii
Depends on oxidation state
Osmium (Os)
Tungsten (W)
Across a period in the d-block, atomic radius decreases as nuclear charge increases. Tungsten is two atomic numbers before osmium, so W has a slightly larger radius than Os.
Which factor primarily causes a decrease in atomic radius across a period?
Relativistic contraction
Increase in principal quantum number
Increase in nuclear charge
Decrease in shielding from d-electrons
As you move across a period, protons are added to the nucleus, increasing nuclear charge. This stronger attraction pulls electrons closer, reducing atomic radius. Shielding remains relatively constant across the period.
Among the 5th-period transition metals Y, Zr, Nb, and Mo, which has the largest atomic radius?
Molybdenum (Mo)
Yttrium (Y)
Niobium (Nb)
Zirconium (Zr)
Within a period, atomic radius decreases with increasing atomic number due to greater nuclear charge. Yttrium is the first of the 5th-period transition metals listed, so it has the largest radius.
Which effect explains why gallium (Ga) has a smaller atomic radius than expected compared to its neighbor zinc (Zn)?
Relativistic contraction
Poor shielding by 3d electrons (d-block contraction)
Lanthanide contraction
Spin-pairing energy
Gallium's filled 3d electrons do not shield the nuclear charge effectively, leading to a stronger pull on the outer electrons and a smaller atomic radius. This phenomenon is known as d-block or d-subshell contraction.
Which heavy element shows significant relativistic contraction of its 6s orbitals, resulting in a smaller atomic radius than expected?
Mercury (Hg)
Thallium (Tl)
Gold (Au)
Lead (Pb)
In gold, relativistic effects cause the 6s electrons to move at speeds approaching a significant fraction of the speed of light, contracting the orbital and reducing the atomic radius. This relativistic contraction is responsible for gold's unusual color and chemistry.
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Study Outcomes

  1. Analyze periodic trends in atomic radius -

    Examine how atomic radius varies across periods and down groups, using periodic table radius questions to reinforce your understanding of group and period trends.

  2. Identify which atom has the largest atomic radius -

    Answer "of the following which atom has the largest atomic radius" questions by applying principles of effective nuclear charge, shielding, and electron-electron repulsion.

  3. Apply effective nuclear charge concepts -

    Understand the role of nuclear charge and electron shielding in determining atomic size and use this knowledge to tackle atomic radius quiz items accurately.

  4. Correlate atomic radius with molecular structure -

    Relate atomic size to bond lengths and molecular geometry within the atomic and molecular structure quiz, improving your interpretation of molecular structure trivia.

  5. Evaluate quiz strategies for periodic trends -

    Develop test-taking techniques for periodic table radius questions and the atomic radius quiz, enhancing your confidence and speed when facing similar challenges.

Cheat Sheet

  1. Group Trend: Radius Increases Down a Column -

    As you move down a group in the periodic table, each element gains an extra electron shell, so the atomic radius grows (source: NIST). For your atomic and molecular structure quiz, remember "Down we go, the radius will grow" to recall why cesium is larger than sodium. This rule helps answer periodic table radius questions quickly and confidently.

  2. Period Trend: Radius Decreases Across a Row -

    Across a period from left to right, protons are added without a new shell, increasing nuclear attraction and pulling electrons closer (Atkins' Physical Chemistry textbook). That's why oxygen is smaller than carbon, even though both sit in period 2. Knowing this inverse trend is crucial for the atomic radius quiz section.

  3. Effective Nuclear Charge (Zeff) Determines Pull -

    Effective nuclear charge, Zeff = Z - S (where Z is the atomic number and S is shielding electrons), quantifies how strongly nucleus attracts valence electrons (Slater's rules via IUPAC). Higher Zeff shrinks atomic radius, as seen moving across a period. Mastering this formula lets you predict and explain radius variations on molecular structure trivia.

  4. Different Radius Definitions Matter -

    Atomic radius can refer to covalent, van der Waals, or metallic types (CRC Handbook of Chemistry and Physics). Covalent radius applies in bonded atoms, while van der Waals radius measures nonbonded contact distance. Recognizing which definition a quiz question demands ensures accurate answers every time.

  5. Largest Atomic Radius Example: Francium vs. Cesium -

    In practical quizzes, cesium (Cs) is often cited as the atom with the largest stable radius, but francium (Fr) surpasses it theoretically (NIST data). A handy mnemonic is "Freaky Francium Far-Out," highlighting Fr's ultimate size at the bottom of Group 1. Use that to ace the "of the following which atom has the largest atomic radius" challenge!

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