Question detail
Explain the trend in atomic radius across Period 3 of the periodic table. Include the role of proton number and electron shielding in your answer.
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
Question
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exam_style
Style
Topic
Periodicity
Question
Explain the trend in atomic radius across Period 3 of the periodic table. Include the role of proton number and electron shielding in your answer.
Answer
As you move across Period 3 from sodium to argon, the atomic radius decreases. This is due to the increase in proton number, which leads to a greater positive charge in the nucleus. The increased nuclear charge pulls the electrons closer to the nucleus, reducing the atomic radius. Additionally, the effect of electron shielding remains relatively constant across this period, as the added electrons are in the same energy level.
Explanation
This answer is strong because it clearly links the trend in atomic radius to the concepts of proton number and electron shielding, demonstrating an understanding of how these factors influence atomic structure. The question tests the student's ability to connect periodic trends with underlying atomic theory.
Common mistake
Confusing Atomic Radius Trends
Students often incorrectly state that atomic radius decreases across Period 3 due to increased electron shielding rather than increased nuclear charge.
To explain the trend in atomic radius across Period 3, use the following reasoning: The atomic radius decreases as you move from sodium (Na) to argon (Ar) because the proton number increases, leading to a greater nuclear charge that pulls the electrons closer to the nucleus, outweighing any effects of electron shielding. Therefore, the atomic radius trend can be summarized as follows: 1. **Formula/Rule**: Atomic radius decreases across a period due to increased nuclear charge. 2. **Substitution**: As you move from Na (11 protons) to Ar (18 protons), the nuclear charge increases from +11 to +18. 3. **Working**: The increased nuclear charge results in a stronger attraction between the nucleus and the electron cloud, leading to a smaller atomic radius. 4. **Answer**: The atomic radius decreases across Period 3. 5. **Units/Conclusion**: The trend is observed in picometers (pm) or nanometers (nm), confirming that atomic radius decreases as you move from left to right across the period.
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