Multiple Choice
Which element has the ground state electron configuration [Kr] 5s^2 4d^{10} 5p^2?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following electron configurations for neutral atoms represents an excited state?
A
1s^2 2s^2 2p^5 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
Verified step by step guidance1
Understand that an excited state electron configuration occurs when electrons occupy higher energy orbitals before lower energy orbitals are completely filled, violating the Aufbau principle.
Review the given electron configurations and identify the order in which orbitals are filled according to the Aufbau principle: 1s, 2s, 2p, 3s, etc.
Check each configuration to see if electrons fill lower energy orbitals completely before occupying higher energy orbitals. For example, 1s^2 2s^2 2p^6 is a ground state because all lower orbitals are fully occupied.
Focus on the configuration 1s^2 2s^2 2p^5 3s^1, where the 2p orbital is not fully filled (only 5 electrons instead of 6) but there is an electron in the higher energy 3s orbital, indicating an electron has been promoted to a higher energy level.
Conclude that the configuration with an electron in 3s while 2p is not full represents an excited state, as it violates the normal filling order.
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