Multiple Choice
How many occupied electron shells does a neutral oxygen atom have in its ground-state electron configuration?
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9. Electrons in Atoms and the Periodic Table
Electronic Structure: Shells
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Fluorine has atomic number 9. How many electron shells (principal energy levels) are occupied in a ground-state fluorine atom?
A
9
B
3
C
1
D
2
Verified step by step guidance1
Recall that the atomic number of an element tells you the number of protons in its nucleus, and for a neutral atom, it also equals the number of electrons.
Understand that electrons occupy energy levels or shells around the nucleus, labeled as principal quantum numbers n = 1, 2, 3, etc.
Determine the electron configuration of fluorine (atomic number 9) by filling electrons into shells starting from the lowest energy level: the first shell (n=1) can hold up to 2 electrons, and the second shell (n=2) can hold up to 8 electrons.
Since fluorine has 9 electrons, place 2 electrons in the first shell and the remaining 7 electrons in the second shell.
Conclude that fluorine has electrons in two shells, so the number of occupied electron shells (principal energy levels) is 2.
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