University Physics with Modern Physics (14th Edition)

Published by Pearson
ISBN 10: 0321973615
ISBN 13: 978-0-32197-361-0

Chapter 41 - Quantum Mechanics II: Atomic Structure - Problems - Discussion Questions - Page 1401: Q41.8


The Pauli exclusion principle demands it.

Work Step by Step

No two electrons are allowed to occupy the same quantum mechanical state in the helium atom. In the ground state, both electrons have n = 1. Then there is only one possible value for the orbital quantum number, l = 0, and only one possibility for the orbital magnetic quantum number, $m_l=0$. The two electrons cannot share every quantum number, so the fourth possibility, spin, must differ. One must be "spin up" and the other must be "spin down".
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