Multiple Choice
Which of the following best describes the trend in atomic radius across a period from left to right on the periodic table?
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10. Periodic Properties of the Elements
Periodic Trend: Atomic Radius
Multiple Choice
In which of the following atoms is the 3s orbital closest to the nucleus?
A
Al
B
Mg
C
Si
D
Na
Verified step by step guidance1
Recall that the 3s orbital refers to the principal quantum number n = 3 and the s subshell, which is spherical and closest to the nucleus within that energy level.
Understand that the effective nuclear charge (Z_eff) experienced by an electron affects how tightly the electron is held and thus how close the orbital is to the nucleus. A higher Z_eff pulls the orbital closer.
Compare the elements given: Na (Z=11), Mg (Z=12), Al (Z=13), and Si (Z=14). As the atomic number increases, the number of protons increases, which generally increases Z_eff for electrons in the same shell.
Consider electron shielding: electrons in inner shells shield outer electrons from the full nuclear charge. Since all these elements have electrons in the same 3s orbital, the difference in Z_eff mainly comes from the increasing nuclear charge with relatively similar shielding.
Conclude that the 3s orbital in Mg is closest to the nucleus because Mg has a higher effective nuclear charge than Na but fewer electrons than Al and Si, resulting in less electron-electron repulsion and a more tightly held 3s orbital.
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