Multiple Choice
Which of the following is the correct electron configuration for argon (Ar)?
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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 (Ca)?
A
1s^2 2s^2 2p^6 3s^2 3p^6 3d^10
B
1s^2 2s^2 2p^6 3s^2 3p^6 3d^2
C
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2
D
1s^2 2s^2 2p^6 3s^2 3p^6 4p^2
Verified step by step guidance1
Step 1: Determine the atomic number of calcium (Ca), which tells you the total number of electrons in a neutral atom. Calcium has an atomic number of 20, so it has 20 electrons.
Step 2: Recall the order in which electron orbitals are filled according to the Aufbau principle. The filling order is: 1s, 2s, 2p, 3s, 3p, 4s, then 3d, and so on.
Step 3: Begin filling the orbitals with electrons, starting from the lowest energy level. Fill 1s with 2 electrons, 2s with 2 electrons, 2p with 6 electrons, 3s with 2 electrons, and 3p with 6 electrons. This accounts for 18 electrons so far.
Step 4: After filling the 3p orbital, the next electrons go into the 4s orbital before the 3d orbital because 4s is lower in energy than 3d. Therefore, the remaining 2 electrons fill the 4s orbital.
Step 5: Combine all the filled orbitals to write the ground state electron configuration for calcium as $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$.
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