Multiple Choice
Which of the following electron configurations represents an excited-state nitrogen atom?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following represents the ground-state electron configuration for cesium (Cs)?
A
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 6p^1
B
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 6s^1
C
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 5d^1
D
[Xe] 6s^2
Verified step by step guidance1
Step 1: Identify the atomic number of cesium (Cs), which is 55. This tells us that a neutral cesium atom has 55 electrons to arrange in its ground-state electron configuration.
Step 2: Recall the order of filling electron orbitals according to the Aufbau principle, which states that electrons fill orbitals starting from the lowest energy level to higher ones. The general order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, etc.
Step 3: Write the electron configuration by filling orbitals in order until you reach 55 electrons. Note that the noble gas xenon (Xe) has 54 electrons, so cesium's configuration will be that of xenon plus one more electron.
Step 4: Recognize that after the 5p^6 orbital (which completes xenon), the next electron goes into the 6s orbital, not the 6p or 5d orbitals, because 6s is lower in energy than 5d or 6p for cesium.
Step 5: Therefore, the ground-state electron configuration for cesium is the same as xenon plus one electron in the 6s orbital, which can be written as: $[Xe] 6s^1$ or fully expanded as $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 6s^1$.
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