Explain why the atomic radius of sodium (Na) is larger than that of magnesium (Mg), even though they belong to the same period.
Answer
Because sodium has a larger atomic radius due to a lower effective nuclear charge on its valence electrons.
The correct answer is Because sodium has a larger atomic radius due to a lower effective nuclear charge on its valence electrons. — Therefore Na has a larger atomic radius than Mg.
Step-by-step solution
- Na and Mg are in period 3, so their valence electrons occupy the same n=3 shell.
- Na has electron configuration 1s²2s²2p⁶3s¹, while Mg has 1s²2s²2p⁶3s².
- Both have similar shielding from inner shells; the difference lies in nuclear charge: Na has 11 protons, Mg has 12.
- The higher nuclear charge in Mg pulls its electrons closer, reducing its radius.
- Therefore Na has a larger atomic radius than Mg.
Common mistake: Assuming more electrons always mean smaller radius
Concept tested: Atomic radius trend
Published · How this solution was prepared and checked
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