Binding order
The bond order (bond degree) denotes the number of effective bonds in a molecule . It is defined as half of the number that results from the difference between binding and antibonding valence electrons (in the molecular orbitals ):
In diatomic molecules it can be determined whether there is a single , double or triple bond . It can also be explained why an He 2 molecule is not stable, since the calculation of the hypothetical molecule results in a formal bond order of zero.
Examples
| Binding order | Number of binding electrons | Name of the bond | Examples elements | Examples CC bonds in hydrocarbons and other bonds |
|---|---|---|---|---|
| 0 | 0 | no binding | Neon ne | Methane : no CC bond |
| 0.5 | 1 | half bond | Dihydrogen cation H 2 + | |
| 1 | 2 | Single bond | Difluor F 2 | Ethane : C – C single bond |
| 1.5 | 3 | One and a half bond | Ozone O 3 | Benzene : Mesomerism between single and double bonds |
| 2 | 4th | Double bond | Dioxygen O 2 | Ethene : C = C double bond |
| 2.5 | 5 | Two and a half bond | Nitric oxide : N = O | |
| 3 | 6th | Triple bond | Dinitrogen N 2 | Ethyne : C☰C triple bond |
Bond order in the oxygen molecule O 2
Electronic configuration of the two atoms: 1s 2 , 2s 2 , 2p 4, respectively
The 2s 2 and 2p 4 molecular orbitals are involved in the binding ; H. the 2 + 4 = 6 valence electrons per atom.
In the bonding, the 2s form 2 orbitals a binding σ-MO (Sigma-molecular orbital) and an antibonding σ * MO (Sigma-molecular orbital) with 2 electrons: ,
The 2p 4 orbitals form a binding σ-MO and 2 binding π-MO with 2 electrons from, the remaining 2 electrons occupy each a π * antibonding molecular orbital: .
Overall, there is a bond order of:
- ,
d. H. the normal oxygen molecule has a double bond.
literature
- Peter W. Atkins, Julio de Paula: Physical Chemistry , 4th Edition, Wiley-VCH, Weinheim 2006, p. 425, ISBN 978-3-527-31546-8
- Erwin Riedel / Christoph Janiak: Inorganische Chemie, 7th edition, de Gruyter, Berlin 2007, p. 145, ISBN 978-3-11-018903-2