Question

If the electronic configuration of nitrogen had $1s^7$, it would have energy lower than that of the normal ground state configuration $1s^{2}2s^{2}2p^3$ because the electrons would be closer to the nucleus. Yet $1s^7$ is not observed because it violates:

• A. Heisenberg uncertainty principle
• B. Hund's rule
• C. Pauli's exclusion principle
• D. Bohr postulates of stationary orbits

Answer 1

Answer: (C)

Pauli's exclusion principle

$1s^7$ is not observed because it violates Pauli's exclusion principle which states that "two electrons in an atom cannot have the same set of all four quantum numbers". In other words, "only two electrons may exist in the same orbital with three quantum numbers same i.e the fourth quantum number different and these electrons have opposite spin."