Multiple Choice
How does the electron-cloud model describe electrons in an 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 atom in an excited state?
A
1s^2 2s^2 2p^6 3s^2
B
1s^2 2s^2 2p^6 3s^1
C
1s^2 2s^2 2p^6
D
1s^2 2s^2 2p^6 3s^1 3p^1
Verified step by step guidance1
Step 1: Understand the concept of 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: Recall the Aufbau principle, Hund's rule, and Pauli exclusion principle to determine the correct order of filling orbitals: electrons fill orbitals from lower to higher energy levels, each orbital gets one electron before pairing, and no two electrons in the same orbital have the same spin.
Step 3: Analyze the given configurations to see if they follow the expected filling order. For example, the configuration 1s^2 2s^2 2p^6 3s^2 is a typical ground state for elements like magnesium, where the 3s orbital is fully occupied before moving to 3p.
Step 4: Identify the configuration that does not follow the expected filling order or has electrons in higher energy orbitals while lower ones are not fully occupied. The configuration 1s^2 2s^2 2p^6 3s^1 3p^1 shows an electron in the 3p orbital while the 3s orbital is not fully occupied, indicating an excited state.
Step 5: Conclude that the configuration 1s^2 2s^2 2p^6 3s^1 3p^1 represents an excited state because it violates the normal filling order by placing an electron in the 3p orbital before completely filling the 3s orbital.
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