chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, an electron pair or Lewis pair consists of two

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

s that occupy the same molecular orbital but have opposite

spins The spins (as in having "the spins") is an adverse reaction of Substance intoxication, intoxication that causes a state of vertigo and nausea, causing one to feel as if "spinning out of control", especially when lying down. It is most commonly as ...

. Gilbert N. Lewis introduced the concepts of both the electron pair and the covalent bond in a landmark paper he published in 1916. MO-covalent and polar bonds

Because electrons are

fermion In particle physics, a fermion is a subatomic particle that follows Fermi–Dirac statistics. Fermions have a half-integer spin (spin 1/2, spin , Spin (physics)#Higher spins, spin , etc.) and obey the Pauli exclusion principle. These particles i ...

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

quantum number In quantum physics and chemistry, quantum numbers are quantities that characterize the possible states of the system. To fully specify the state of the electron in a hydrogen atom, four quantum numbers are needed. The traditional set of quantu ...

s. Therefore, for two electrons to occupy the same orbital, and thereby have the same orbital quantum number, they must have different spin quantum numbers. 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 A chemical bond is the association of atoms or ions to form molecules, crystals, and other structures. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds or through the sharing of electrons a ...

between two atoms, or they can occur as a lone pair 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 for electrons to 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 'sea'.

References

{{DEFAULTSORT:Electron Pair Quantum chemistry Chemical bonding Molecular physics

See also

References