Multiple Choice
How many electrons occupy the 4p orbitals in a neutral vanadium (V) 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 of calcium (atomic number 20)?
A
1s^2 2s^2 2p^6 3s^2 3p^6 4p^2
B
1s^2 2s^2 2p^6 3s^2 3p^6 3d^10
C
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2
D
1s^2 2s^2 2p^6 3s^2 3p^6 3d^2
Verified step by step guidance1
Identify the atomic number of calcium, which is 20. This means calcium has 20 electrons in its neutral ground state.
Recall the order in which electron orbitals are filled according to the Aufbau principle: 1s, 2s, 2p, 3s, 3p, 4s, then 3d.
Fill the orbitals with electrons following this order until all 20 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 4s^2 (2 electrons).
Note that the 3d orbitals start filling after the 4s orbital is filled, so for calcium, which has 20 electrons, the 3d orbitals remain empty in the ground state.
Write the full ground-state electron configuration for calcium as $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$, confirming that this matches the correct answer.
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