Multiple Choice
In the ground state electron configuration of zinc (Zn), how many electrons occupy the 3d sublevel?
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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 selenium (atomic number 34)?
A
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^8 4p^6
B
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6
C
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^2
D
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^4
Verified step by step guidance1
Identify the atomic number of selenium, which is 34. This means selenium has 34 electrons to be placed in orbitals according to the Aufbau principle.
Recall the order of filling orbitals based on increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on.
Fill the orbitals step-by-step with electrons, respecting the maximum number of electrons each orbital can hold: s (2 electrons), p (6 electrons), d (10 electrons).
Write the electron configuration by adding electrons in order: 1s^2 (2 electrons), 2s^2 (2 electrons), 2p^6 (6 electrons), 3s^2 (2 electrons), 3p^6 (6 electrons), 4s^2 (2 electrons), 3d^10 (10 electrons), and then place the remaining electrons in 4p orbitals.
Since selenium has 34 electrons, after filling up to 3d^10, place the remaining 4 electrons in the 4p orbital, resulting in 4p^4. This gives the full configuration: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^4$.
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