Multiple Choice
Which of the following is the correct electron configuration for potassium (K)?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following electron configurations could represent a sodium atom (Na) in an excited state?
A
1s^2 2s^2 2p^6 2d^1
B
1s^2 2s^2 2p^6 3s^1
C
1s^2 2s^2 2p^6 3p^1
D
1s^2 2s^2 2p^5 3s^2
Verified step by step guidance1
Recall that the ground state electron configuration of sodium (Na), which has 11 electrons, is $1s^2 2s^2 2p^6 3s^1$. This means all lower energy orbitals are fully filled before electrons occupy higher energy orbitals.
Understand that an excited state configuration occurs when one or more electrons are promoted to higher energy orbitals than in the ground state, but the total number of electrons remains the same.
Check each given configuration to see if it has 11 electrons in total and if the electron distribution follows the allowed orbitals for sodium:
- $1s^2 2s^2 2p^6 2d^1$: The $2d$ orbital does not exist because the d orbitals start at the third energy level (n=3), so this configuration is invalid.
- $1s^2 2s^2 2p^6 3s^1$: This is the ground state configuration, not an excited state.
- $1s^2 2s^2 2p^6 3p^1$: This configuration has the electron promoted from $3s$ to $3p$, which is a valid excited state.
- $1s^2 2s^2 2p^5 3s^2$: This configuration has one less electron in $2p$ and one extra in $3s$, which is possible as an excited state but must be checked for total electrons and allowed electron distribution.
Conclude by identifying which configurations are valid excited states based on electron count, allowed orbitals, and promotion of electrons from lower to higher energy orbitals.
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