Michael Blaber, PhD
Florida State University: Electronic Structure of Atoms: Electron Configurations
Florida State University provides this article on electronic configurations of atoms and Hund's rule.
Georgia State University
Georgia State University: Hyper Physics: Hund's Rules
A complete overview of Hund's rules including exceptions.
University of Maryland
Um: Quantum Mechanics of One and Two Electron Atoms
An explanation of Hund's rule and how to apply it to quantum mechanics. A mathematical-based explanation.
Sophia Learning
Sophia: Paired and Unpaired Electrons: Lesson 2
This lesson will point out the difference between electron pairs and unpaired electrons in an atom using orbital diagrams. It is 2 of 3 in the series titled "Paired and Unpaired Electrons."