electronpairing

Electron pairing refers to two electrons occupying the same quantum state, typically an atomic or molecular orbital, with opposite spins. According to the Pauli exclusion principle, two electrons can share an orbital only if their spins are antiparallel. In atoms and molecules, many electrons exist as pairs: bonding pairs that participate in covalent bonds, and lone pairs that reside on a particular atom without forming bonds.

In valence-shell and molecular orbital theories, pairing determines structure and reactivity. Paired electrons contribute to diamagnetism, while unpaired electrons yield paramagnetism. The arrangement into paired or unpaired electrons influences bond angles and shapes via repulsion between electron pairs (as described by VSEPR), and it governs bonding, reactivity, and electronic properties of molecules.

Electron pairing is also a central concept in condensed matter physics. In conventional superconductors, electrons near the Fermi surface form Cooper pairs mediated by lattice vibrations (phonons). These pairs, typically in a spin-singlet state with opposite momenta, condense into a coherent ground state that allows resistance-free electrical flow. Some materials exhibit unconventional pairing, including spin-triplet configurations, which can lead to different superconducting properties.

In chemistry, forming paired electrons generally lowers the system’s energy and stabilizes structures; breaking a pair requires energy and can generate radicals or reactive intermediates. The concept of electron pairing, therefore, links electronic structure, magnetic behavior, chemical bonding, and emergent phenomena in solids.