Multiple Choice
Which atom has the electron configuration 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10}?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following is the electron configuration of a neutral potassium (K) atom?
A
1s^2 2s^2 2p^6 3s^2 3p^6 4s^1
B
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2
C
1s^2 2s^2 2p^6 3s^2 3p^5 4s^2
D
1s^2 2s^2 2p^6 3s^2 3p^6 3d^1
Verified step by step guidance1
Identify the atomic number of potassium (K), which tells you the number of electrons in a neutral atom. Potassium has an atomic number of 19, so it has 19 electrons.
Recall the order in which electron orbitals are filled according to the Aufbau principle: 1s, 2s, 2p, 3s, 3p, 4s, then 3d.
Distribute the 19 electrons into the orbitals following this order, filling each orbital to its maximum capacity before moving to the next: 1s (2 electrons), 2s (2 electrons), 2p (6 electrons), 3s (2 electrons), 3p (6 electrons), and then 4s (1 electron).
Note that the 4s orbital fills before the 3d orbital because it is lower in energy for potassium, so the 19th electron goes into 4s, not 3d.
Write the full electron configuration by combining all filled orbitals with their electron counts: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^1$.
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