Question

determine which of the following electron configurations are not valid:

1. 1s²2s²2p⁶3s²3p⁶4s²4d¹⁰4p⁵
2. 1s²2s²2p⁶3s³3d⁵
3. ra 7s²5f⁸
4. kr 5s²4d¹⁰5p⁵
5. xe

Explanation:

Step1: Analyze electron configuration rules

Electron configurations must follow the Aufbau principle (filling orbitals in order of increasing energy), Pauli exclusion principle (each orbital can hold at most 2 electrons with opposite spins), and Hund's rule (electrons occupy degenerate orbitals singly before pairing). Also, orbital capacities: \(s\) - 2 electrons, \(p\) - 6 electrons, \(d\) - 10 electrons, \(f\) - 14 electrons.

Step2: Check each configuration

• 16) \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}4d^{10}4p^{5}\): After \(4s\), it should be \(3d\) before \(4p\) (Aufbau principle violation).
• 17) \(1s^{2}2s^{2}2p^{6}3s^{3}3d^{5}\): \(3s\) can hold at most 2 electrons (Pauli exclusion principle violation).
• 18) \([Ra]7s^{2}5f^{8}\): \(Ra\) is in period 7, but \(5f\) is filled after \(6d\) (Aufbau principle violation).
• 19) \([Kr]5s^{2}4d^{10}5p^{5}\): Follows Aufbau, Pauli, and Hund's rules.
• 20) \([Xe]\): Incomplete (no valence - shell electrons specified).

Answer:

1. Invalid (Aufbau principle violation).
2. Invalid (Pauli exclusion principle violation).
3. Invalid (Aufbau principle violation).
4. Valid.
5. Invalid (incomplete).