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Electron pair

 

 
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Electron pair
 
 
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In chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
, an electron pair consists of two electrons that occupy the same orbital
Molecular orbital

In chemistry, a molecular orbital is a mathematical function that describes the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region....
 but have opposite spins.

Because electrons are fermion
Fermion

In particle physics, fermions are subatomic particle which obey Fermi-Dirac statistics; they are named after Enrico Fermi. In contrast to bosons, which have Bose-Einstein statistics, only one fermion can occupy a quantum state at a given time; this is the Pauli Exclusion Principle....
s, the Pauli exclusion principle
Pauli exclusion principle

The Pauli exclusion principle is a quantum mechanics principle formulated by Wolfgang Pauli in 1925. It states that no two identical particles fermions may occupy the same quantum state simultaneously....
 forbids these particles from having exactly the same quantum numbers. Therefore the only way to occupy the same orbital, i.e. have the same orbital quantum numbers, is to differ in the spin quantum number. This limits the number of electrons in the same orbital to exactly two.

The pairing of spins is often energetically favorable and electron pairs therefore play a very large role in chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
.






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In chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
, an electron pair consists of two electrons that occupy the same orbital
Molecular orbital

In chemistry, a molecular orbital is a mathematical function that describes the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region....
 but have opposite spins.

Because electrons are fermion
Fermion

In particle physics, fermions are subatomic particle which obey Fermi-Dirac statistics; they are named after Enrico Fermi. In contrast to bosons, which have Bose-Einstein statistics, only one fermion can occupy a quantum state at a given time; this is the Pauli Exclusion Principle....
s, the Pauli exclusion principle
Pauli exclusion principle

The Pauli exclusion principle is a quantum mechanics principle formulated by Wolfgang Pauli in 1925. It states that no two identical particles fermions may occupy the same quantum state simultaneously....
 forbids these particles from having exactly the same quantum numbers. Therefore the only way to occupy the same orbital, i.e. have the same orbital quantum numbers, is to differ in the spin quantum number. This limits the number of electrons in the same orbital to exactly two.

The pairing of spins is often energetically favorable and electron pairs therefore play a very large role in chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
. They can form
  1. a chemical bond
    Chemical bond

    A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds....
     between two atoms
  2. as a lone pair
    Lone pair

    A lone pair is a valence electron pair without bonding or sharing with other atoms. They are found in the outermost electron shell of an atom, so lone pairs are a subset of a molecule's valence electrons....
    .
  3. fill the core levels
    Core electron

    Core Electrons: the electrons in the inner part of the atom that are not valence electrons and therefore do not participate in bonding. An example is carbon: Carbon has a total of 6 electrons, 4 of which are valence electrons, so the remaining 2 electrons must be core electrons....
     of an atom.


Because the spins are paired the magnetic moment of the electrons cancels and the contribution of the pair to the magnetic properties will in general be a diamagnetic one
Diamagnetism

Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied magnetic field, thus causing a repulsive effect....
.

Although a strong tendency to pair off electrons can be observed in chemistry, it is also possible that electrons occur as unpaired electron
Unpaired electron

In chemistry an unpaired electron is an electron that occupies an orbital singly, rather than as part of an electron pair.As the formation of electron pairs is often energetically favorable, either in the form of a chemical bond or as a lone pair, unpaired electrons are relatively uncommon in chemistry, because an entity that carries an u...
s.

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

Superconductivity is a phenomenon occurring in certain materials generally at very low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field ....
: the formation of Cooper pair
Cooper pair

In condensed matter physics, a Cooper pair is the name given to electrons that are bound together at low temperatures in a certain manner first described in 1956 by Leon Cooper....
s.

See also

  • Polyhedral skeletal electron pair theory
    Polyhedral skeletal electron pair theory

    In chemistry the polyhedral skeletal electron pair theory provides electron counting rules used to predict the structure of electron deficient cluster compound....