Pairing
Definition and meaning of Pairing in chemistry.
Pairing refers to the process where two electrons with opposite spins occupy the same atomic or molecular orbital. According to the Pauli exclusion principle, an orbital can hold a maximum of two electrons, and they must have opposite spin states.
In more detail
When electrons are placed into degenerate orbitals, Hund's rule states that they will first occupy empty orbitals singly before pairing occurs. The pairing energy is the energy required to overcome the electrostatic repulsion between two negatively charged electrons occupying the same region of space. In transition metal complexes, the balance between crystal field splitting energy and pairing energy determines whether a complex will be high spin or low spin. The concept of pairing is fundamental to predicting magnetic properties and chemical reactivity.
Key facts
| Field | Physical Chemistry |
|---|---|
| Governing Principle | Pauli exclusion principle |
| Spin Requirement | Opposite spins |
In a neutral carbon atom, the 2p orbitals contain two unpaired electrons, while a full 1s orbital exhibits complete electron pairing.
Frequently asked questions
Why does electron pairing require energy?
Electrons are negatively charged, so forcing two of them into the same orbital requires energy to overcome their mutual repulsion.
How does this affect magnetism?
Atoms with unpaired electrons are generally paramagnetic, while those with only paired electrons are diamagnetic.