Fix any errors in these proposed electron configurations_ number of electrons in atom proposed electron configuration 20 Is” 2s 2p 3s’ Jp” 34? 30 Is Ip 2s” 2p” 2d 3s” 3p 14 Is” 2s” 2p” 2d 3s
The Correct Answer and Explanation is:
1. Atomic number 20 (Calcium, Ca):
Proposed electron configuration:
1s² 2s² 2p⁶ 3s² 3p⁴
This configuration is incorrect because the 3p orbital can hold a maximum of 6 electrons. Calcium (with 20 electrons) should have a configuration that fills the orbitals up to 4s².
Correct electron configuration:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
2. Atomic number 34 (Selenium, Se):
Proposed electron configuration:
1s² 2s² 2p⁶ 3s² 3p⁴ 3d¹⁰
This is close but slightly incorrect. The 3d orbital fills after the 4s orbital according to the Aufbau principle. For selenium (34 electrons), the correct configuration should have filled the 4s orbital before the 3d orbital.
Correct electron configuration:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴
3. Atomic number 14 (Silicon, Si):
Proposed electron configuration:
1s² 2s² 2p⁶ 3s²
This configuration is incomplete because silicon (atomic number 14) has 14 electrons, but the proposed configuration only accounts for 12.
Correct electron configuration:
1s² 2s² 2p⁶ 3s² 3p²
Explanation:
- The Aufbau principle states that electrons fill orbitals starting from the lowest energy level (1s) and proceed to higher levels (2s, 2p, 3s, 3p, 4s, 3d, etc.) in a systematic order.
- The Pauli exclusion principle ensures that no two electrons in the same atom have the same set of quantum numbers, which is why orbitals fill with two electrons (one with spin-up and the other with spin-down).
- Hund’s rule states that electrons fill degenerate orbitals (orbitals with the same energy level, like 3p or 5p) singly before pairing up to minimize repulsion.
So, the corrected electron configurations are based on filling the orbitals correctly according to these rules.
