- Electron pair
In chemistry, an electron pair consists of two electrons that occupy the same orbital but have opposite spins.
Because electrons are
fermion s, thePauli exclusion principle 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 . They can form
# achemical bond between two atoms
# as alone pair .
# fill the core levels 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.
Although a strong tendency to pair off electrons can be observed in chemistry, it is also possible that electrons occur as
unpaired electron 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 : the formation ofCooper pair s.ee also
*
Polyhedral skeletal electron pair theory
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