Questions on Atomic Radius
Multiple-Choice Questions: Atomic Radius
🔹 Basic Concepts
1. What is atomic radius?
A) The distance between nucleus and outermost electron
B) The weight of the atom
C) The number of protons in an atom
D) The number of neutrons in an atom
E) The total number of electrons
2. Which element has the largest atomic radius in Period 2?
A) Lithium (Li)
B) Fluorine (F)
C) Oxygen (O)
D) Nitrogen (N)
E) Neon (Ne)
3. What is the general trend of atomic radius across a period from left to right?
A) It increases
B) It decreases
C) It remains constant
D) It fluctuates randomly
E) It doubles
4. What is the trend of atomic radius down a group in the periodic table?
A) It decreases
B) It remains the same
C) It increases
D) It fluctuates
E) It halves
5. Why does atomic radius decrease across a period?
A) Increase in nuclear charge pulls electrons closer
B) Addition of electron shells
C) Decrease in number of protons
D) Increase in electron repulsion
E) Shielding effect increases
🔹 Periodic Table Relationships
6. Which has the smallest atomic radius?
A) Sodium (Na)
B) Aluminum (Al)
C) Chlorine (Cl)
D) Argon (Ar)
E) Magnesium (Mg)
7. Which element has the largest atomic radius in Group 1?
A) Lithium (Li)
B) Sodium (Na)
C) Potassium (K)
D) Rubidium (Rb)
E) Cesium (Cs)
8. Which of the following would have the smallest atomic radius?
A) O²⁻
B) F⁻
C) Ne
D) Na⁺
E) Mg²⁺
9. In a period, as atomic number increases, atomic radius typically:
A) Decreases
B) Increases
C) Stays the same
D) Increases then decreases
E) Is unpredictable
10. What causes the atomic radius to increase down a group?
A) Increased nuclear charge
B) Increased shielding and addition of electron shells
C) Decrease in mass number
D) More isotopes
E) Increased proton repulsion
🔹 Cations and Anions
11. Which has the largest radius among these?
A) Cl⁻
B) Cl
C) Cl⁺
D) Ar
E) K⁺
12. When a neutral atom becomes a cation, its radius:
A) Increases significantly
B) Stays the same
C) Decreases
D) Doubles
E) Becomes negative
13. Which ion has the smallest radius?
A) Na⁺
B) Mg²⁺
C) Al³⁺
D) K⁺
E) Ca²⁺
14. Why is an anion larger than its parent atom?
A) Fewer protons
B) More protons
C) Additional electrons increase repulsion
D) More neutrons are added
E) Energy levels are removed
15. What happens to the atomic radius of a neutral atom when it gains electrons?
A) It decreases
B) It becomes zero
C) It increases
D) It stays constant
E) It becomes a cation
🔹 Comparisons and Exceptions
16. Which of the following atoms has the largest atomic radius?
A) N
B) P
C) As
D) Sb
E) Bi
17. Which is true about atomic radii of noble gases?
A) They are the largest in each period
B) They are the smallest in each period
C) They fluctuate randomly
D) They increase across the period
E) They follow no trend
18. What is the atomic radius trend in transition metals?
A) It increases steadily
B) It fluctuates without a pattern
C) It increases then decreases
D) It changes very little across the period
E) It decreases sharply
19. Which group in the periodic table has the largest atomic radii overall?
A) Group 1 (alkali metals)
B) Group 14 (carbon group)
C) Group 17 (halogens)
D) Group 18 (noble gases)
E) Group 2 (alkaline earth metals)
20. Which statement is correct about atomic radius and effective nuclear charge?
A) Higher effective nuclear charge leads to larger radius
B) Atomic radius is independent of nuclear charge
C) Higher effective nuclear charge pulls electrons closer
D) Higher effective nuclear charge pushes electrons away
E) Effective nuclear charge is not related to periodic trends
- Questions on Halogens (Group 17 Elements)
- Questions on Transition Metals (d-block elements)
- Questions on Lanthanides and Actinides
Answers with Extended Explanations
1. A – The distance between nucleus and outermost electron
→ Atomic radius is defined by how far the outermost electrons are from the nucleus.
2. A – Lithium (Li)
→ Atomic radius decreases across the period; Li is at the beginning.
3. B – It decreases
→ Due to increasing nuclear charge with no added energy levels.
4. C – It increases
→ New energy levels are added down a group.
5. A – Increase in nuclear charge pulls electrons closer
→ Electrons are attracted more strongly across a period.
6. D – Argon (Ar)
→ Argon is a noble gas and has the smallest radius due to strong nuclear pull and filled shell.
7. E – Cesium (Cs)
→ It is lowest in Group 1, so has the most energy levels and largest radius.
8. E – Mg²⁺
→ More protons pulling fewer electrons results in the smallest radius.
9. A – Decreases
→ Due to increased pull on electrons with more protons.
10. B – Increased shielding and addition of electron shells
→ More shells lead to larger radii despite higher nuclear charge.
11. A – Cl⁻
→ Gaining an electron increases repulsion and radius.
12. C – Decreases
→ Loss of electrons reduces electron repulsion and radius shrinks.
13. C – Al³⁺
→ The highest positive charge with smallest electron cloud.
14. C – Additional electrons increase repulsion
→ More electron-electron repulsion pushes outer electrons farther.
15. C – It increases
→ More electrons cause expansion of the electron cloud.
16. E – Bi
→ It is at the bottom of Group 15, so has the largest radius.
17. B – They are the smallest in each period
→ Due to full valence shells and maximum nuclear pull.
18. D – It changes very little across the period
→ Electron shielding by d-electrons keeps atomic size nearly constant.
19. A – Group 1 (alkali metals)
→ These have the largest radii in their respective periods.
20. C – Higher effective nuclear charge pulls electrons closer
→ Which reduces the atomic radius.
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