Electron pair

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An electron pair is understood to be two electrons with opposite spin that occupy the same atomic or molecular orbital .

Due to the Pauli principle , electrons within an atom (more precisely: within an electronically closed system) cannot agree in all quantum numbers . For each orbital, which already defines the main quantum number , secondary quantum number and magnetic quantum number of the electrons contained, the only distinguishing feature left is the spin quantum number , which can only assume the values ​​+1/2 and −1/2. This means that the maximum number of different electrons per orbital is limited to two.

The electrons are distributed to the available orbitals according to certain rules (see electron configuration or Hund's rules ). Rule of thumb: a new, energetically higher orbital is only occupied if the energy difference is low; if the difference is greater, the lower-energy orbitals are first occupied with a second electron, forming electron pairs.

Chemical bond

Electron pairs play a special role in chemical bonds : the atomic bond is mediated by bonding electron pairs that are between the two atoms involved and are common to both. Alongside ionic and metallic bonds, this type of bond is the most important.

In contrast, lone pairs of electrons belong to only one atom and, according to the IUPAC recommendation, are represented by two dots for better distinguishability.

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