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 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. Also, orbital capacities: \(s\) - orbital (\(l = 0\)) can hold 2 electrons, \(p\) - orbital (\(l=1\)) can hold 6 electrons, \(d\) - orbital (\(l = 2\)) can hold 10 electrons, \(f\) - orbital (\(l=3\)) can hold 14 electrons.

Step2: Check each configuration

• For \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}4d^{10}4p^{5}\)

The order of filling is wrong. After \(4s\), the next orbitals to fill are \(3d\) and then \(4p\). The correct order should be \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{5}\).

• For \(1s^{2}2s^{2}2p^{6}3s^{3}3d^{5}\)

The \(3s\) orbital can hold a maximum of 2 electrons. Having \(3s^{3}\) violates the Pauli exclusion principle.

• For \([Ra]7s^{2}5f^{8}\)

The noble - gas core \([Ra]\) is incorrect. The \(5f\) orbitals start to fill after \(7s\) and \(6d\). Also, if we consider the general form of electron - configuration writing, the order of orbitals after the noble - gas core should follow the Aufbau order.

• For \([Kr]5s^{2}4d^{10}5p^{5}\)

This configuration is valid. \([Kr]\) represents \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}\). Then \(5s^{2}4d^{10}5p^{5}\) follows the Aufbau principle (\(5s<4d < 5p\)).

• For \([Xe]\)

A single noble - gas core without additional valence - electron orbitals (for a non - noble - gas element) is not a complete electron configuration for an atom (except for the noble gas \(Xe\) itself). But if we assume it is for \(Xe\), it is valid. If it is for another element, it is incomplete. Assuming we are talking about non - noble - gas elements in the context of these problems (since other configurations have valence - electron orbitals), \([Xe]\) (for non - \(Xe\) elements) is not a valid electron configuration.

Answer:

1. Not valid
2. Not valid
3. Not valid
4. Valid
5. Not valid (assuming non - Xe element context)