chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...

, an electron pair or Lewis pair consists of two electrons that occupy the same molecular orbital but have opposite spins.

Gilbert N. Lewis Gilbert Newton Lewis (October 23 or October 25, 1875 – March 23, 1946) was an American physical chemist and a Dean of the College of Chemistry at University of California, Berkeley. Lewis was best known for his discovery of the covalent bond a ...

introduced the concepts of both the electron pair and the

covalent bond A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...

in a landmark paper he published in 1916. MO-covalent and polar bonds

Because electrons are

fermion In particle physics, a fermion is a particle that follows Fermi–Dirac statistics. Generally, it has a half-odd-integer spin: spin , spin , etc. In addition, these particles obey the Pauli exclusion principle. Fermions include all quarks an ...

s, the Pauli exclusion principle forbids these particles from having the same

quantum number In quantum physics and chemistry, quantum numbers describe values of conserved quantities in the dynamics of a quantum system. Quantum numbers correspond to eigenvalues of operators that commute with the Hamiltonian—quantities that can be kno ...

s. Therefore, for two electrons to occupy the same orbital, and thereby have the same orbital quantum number, they must have different

spin quantum number In atomic physics, the spin quantum number is a quantum number (designated ) which describes the intrinsic angular momentum (or spin angular momentum, or simply spin) of an electron or other particle. The phrase was originally used to describe th ...

. This also limits the number of electrons in the same orbital to two. The pairing of spins is often energetically favorable, and electron pairs therefore play a large role in

. They can form a chemical bond between two atoms, or they can occur as a

lone pair In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC ''Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lone ...

of valence electrons. They also fill the core levels of an atom. Because the spins are paired, the magnetic moment of the electrons cancel one another, and the pair's contribution to magnetic properties is generally diamagnetic. Although a strong tendency to pair off electrons can be observed in chemistry, it is also possible that electrons occur as unpaired electrons. In the case of metallic bonding the magnetic moments also compensate to a large extent, but the bonding is more communal so that individual pairs of electrons cannot be distinguished and it is better to consider the electrons as a collective 'ocean'. A very special case of electron pair formation occurs in

superconductivity Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike ...

: the formation of Cooper pairs. In unconventional superconductors, whose crystal structure contains copper anions, the electron pair bond is due to antiferromagnetic

spin Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...

fluctuations.

References

Quantum chemistry Chemical bonding Molecular physics {{AMO-physics-stub

See also

References