Multiple Choice
How many occupied electron shells (principal energy levels) does a neutral aluminum atom have in its ground-state electronic configuration?
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9. Electrons in Atoms and the Periodic Table
Electronic Structure: Shells
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In its ground state, how many occupied electron shells does a neutral sodium atom (Na) have?
A
1
B
4
C
2
D
3
Verified step by step guidance1
Recall that the electron shells correspond to the principal energy levels around the nucleus, labeled as n = 1, 2, 3, etc.
Determine the atomic number of sodium (Na), which is 11, meaning it has 11 electrons in its neutral state.
Distribute these 11 electrons into shells following the order of filling: the first shell (n=1) can hold up to 2 electrons, the second shell (n=2) can hold up to 8 electrons, and the third shell (n=3) can hold up to 18 electrons.
Fill the shells in order: place 2 electrons in the first shell, then 8 electrons in the second shell, and the remaining electrons go into the third shell.
Count how many shells have electrons after this distribution; the number of occupied shells corresponds to the number of shells that contain at least one electron.
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