Multiple Choice
Which of the following is the correct electron configuration for a neutral iron (Fe) atom?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following electron configurations represents an excited state for an atom of calcium?
A
1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^1
B
1s^2 2s^2 2p^6 3s^2 3p^6 4p^2
C
1s^2 2s^2 2p^6 3s^2 3p^6 3d^2
D
1s^2 2s^2 2p^6 3s^2 3p^6 4s^2
Verified step by step guidance1
Recall the ground state electron configuration of calcium (Ca), which has an atomic number of 20. The electrons fill orbitals in order of increasing energy according to the Aufbau principle.
Write the ground state configuration for calcium: $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2$. This shows that the 4s orbital is fully occupied before any 3d orbitals are filled.
Understand that an excited state occurs when one or more electrons occupy higher energy orbitals than in the ground state, leaving lower energy orbitals partially filled or empty.
Examine each given configuration and compare it to the ground state. Look for electrons promoted from the 4s orbital to the 3d or 4p orbitals, which would indicate an excited state.
Identify the configuration where an electron from the 4s orbital is moved to a higher energy orbital (like 3d or 4p), such as $1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^1\ 3d^1$, as this represents an excited state.
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