Multiple Choice
Which atom in the ground state has a stable (completely filled) electron configuration?
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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 atom in the excited state?
A
1s^2 2s^2 2p^6 3s^1
B
1s^2 2s^2 2p^6
C
1s^2 2s^2 2p^6 3s^2
D
1s^2 2s^2 2p^6 3s^1 3p^1
Verified step by step guidance1
Step 1: Understand the difference between ground state and excited state electron configurations. The ground state configuration is the lowest energy arrangement of electrons in an atom, where electrons fill orbitals starting from the lowest energy level following the Aufbau principle.
Step 2: Review the given electron configurations and identify which ones follow the Aufbau principle strictly, meaning electrons fill lower energy orbitals completely before occupying higher energy orbitals.
Step 3: Recognize that an excited state configuration occurs when one or more electrons have been promoted to a higher energy orbital without completely filling the lower energy orbitals first.
Step 4: Analyze the configuration $1s^2 2s^2 2p^6 3s^1 3p^1$. Notice that instead of filling the $3s$ orbital completely before moving to $3p$, there is only one electron in $3s$ and one electron in $3p$, indicating an electron has been excited from $3s$ to $3p$.
Step 5: Conclude that the configuration $1s^2 2s^2 2p^6 3s^1 3p^1$ represents an excited state because it does not follow the normal filling order and shows an electron promoted to a higher energy orbital.
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