Physical chemistry
Molecular orbitals
Linear combinations of atomic orbitals form bonding and antibonding molecular orbitals; filling predicts bond order and magnetism.
In LCAO, atomic wavefunctions combine when symmetry and energy match. Constructive overlap raises internuclear density (bonding); a node gives an antibonding orbital.
LCAO and bond order
Linear combinations of atomic orbitals form bonding and antibonding molecular orbitals; filling predicts bond order and magnetism.
Definition: Core definition
A molecular orbital is an electron state extending over the whole molecule; * marks an antibonding orbital.
Example: Worked example
Apply the model to a simple case: H₂ has two electrons in σ1s and none in σ1s: bond order 1. O₂ has two unpaired electrons in π2p, explaining paramagnetism and bond order 2.
Solution
H₂ has two electrons in σ1s and none in σ1s: bond order 1. O₂ has two unpaired electrons in π2p, explaining paramagnetism and bond order 2.
A molecular orbital is an electron state extending over the whole molecule; * marks an antibonding orbital.
| Quantity | Model / rule |
|---|---|
| Key relation | Linear combinations of atomic orbitals form bonding and antibonding molecular orbitals; filling predicts bond order and magnetism. |
| Meaning / use | H₂ has two electrons in σ1s and none in σ1s: bond order 1. O₂ has two unpaired electrons in π2p, explaining paramagnetism and bond order 2. |
What is the H₂ bond order in the molecular-orbital model?
Which statement best matches the model described?
References
- D. J. Griffiths and D. F. Schroeter (2018). Introduction to Quantum Mechanics