Singlet and Triplet Electrons: Principles, Chemistry, and Key Discoveries

Electrons, the building blocks of chemistry, exhibit behaviors that reveal the fundamental principles of quantum mechanics. Among these behaviors, the singlet and triplet states stand out as essential concepts, defining the spin configurations of paired electrons. This article explores these fascinating states while incorporating insights from groundbreaking scientists like Wolfgang Pauli, Friedrich Hund, and Gilbert N. Lewis, enriched with their enduring wisdom.

What Are Singlet and Triplet States?

"The discovery of quantum mechanics was not just a step forward—it was a leap into a new way of thinking about the universe."
— Paul Dirac

At the heart of molecular interactions lie the singlet and triplet states, which are defined by the spin arrangements of two electrons:

The Singlet State

The singlet state occurs when two electrons occupy the same orbital but have opposite spins (+12+\frac{1}{2} and −12-\frac{1}{2}), resulting in a total spin quantum number (SS) of 0. This is the ground state for most molecules, reflecting the Pauli Exclusion Principle:

"Two electrons cannot exist in the same quantum state simultaneously."
— Wolfgang Pauli

The Triplet State

When electrons have parallel spins they enter the triplet state. This state aligns with Hund’s Rule of Maximum Multiplicity, which states: