Multiple Choice
Which of the following electron configurations represents an atom in the excited state?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following is the correct 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
B
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 5d^1
C
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 6s^1
D
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 6p^1
Verified step by step guidance1
Identify the atomic number of cesium (Cs), which is 55. This means cesium has 55 electrons to be placed in orbitals according to the Aufbau principle.
Recall the order of orbital filling based on increasing energy levels: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, and so on.
Fill the orbitals with electrons following the order above until you reach 55 electrons. Remember that each s orbital can hold 2 electrons, each p orbital 6 electrons, and each d orbital 10 electrons.
Note that after filling the 5p orbital (which accounts for 46 electrons), the next electron goes into the 6s orbital, not the 5d or 6p orbitals, because 6s has lower energy than 5d and 6p.
Write the electron configuration by listing all filled orbitals with their electron counts, ending with 6s^1 to account for the 55th electron.
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