Multiple Choice
Which of the following correctly represents the orbital diagram for arsenic (As, atomic number 33)?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following represents the correct electron configuration for a neutral atom of potassium (atomic number 19)?
A
1s^2 2s^2 2p^6 3s^2 3p^5 4s^2
B
1s^2 2s^2 2p^6 3s^2 3p^6 4p^1
C
1s^2 2s^2 2p^6 3s^2 3p^6 3d^1
D
1s^2 2s^2 2p^6 3s^2 3p^6 4s^1
Verified step by step guidance1
Identify the atomic number of potassium, which is 19. This means a neutral potassium atom has 19 electrons.
Recall the order in which electron orbitals are filled based on the Aufbau principle: 1s, 2s, 2p, 3s, 3p, 4s, then 3d.
Fill the orbitals with electrons following this order until all 19 electrons are placed: 1s^2 (2 electrons), 2s^2 (2 electrons), 2p^6 (6 electrons), 3s^2 (2 electrons), 3p^6 (6 electrons), and then place the remaining electron in the 4s orbital.
Note that the 4s orbital fills before the 3d orbital because it is lower in energy for potassium, so the last electron goes into 4s^1, not 3d^1 or 4p^1.
Compare the given options with the correct electron configuration derived: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1, confirming this is the correct configuration for neutral potassium.
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