Multiple Choice
Which of the following electron configurations is incorrect?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following electron configurations represents an atom of chlorine (atomic number 17) in an excited state?
A
1s^2 2s^2 2p^6 3s^1 3p^6
B
1s^2 2s^2 2p^6 3s^2 3p^4 4s^1
C
1s^2 2s^2 2p^6 3s^2 3p^6
D
1s^2 2s^2 2p^6 3s^2 3p^5
Verified step by step guidance1
Recall that the atomic number of chlorine is 17, which means a neutral chlorine atom has 17 electrons.
Write the ground state electron configuration for chlorine by filling orbitals in order of increasing energy: 1s, 2s, 2p, 3s, and then 3p, until all 17 electrons are placed.
The ground state configuration for chlorine is $1s^2 2s^2 2p^6 3s^2 3p^5$, where the 3p subshell has 5 electrons.
An excited state occurs when one or more electrons are promoted to a higher energy orbital, leaving a lower energy orbital partially filled or less than full.
Compare the given configurations to the ground state: the excited state will have the same total number of electrons (17) but with an electron moved to a higher energy level, such as $3s^1 3p^6$, indicating an electron promoted from 3s to 3p.
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