Valence electron concentration
The valence electron concentration (VEK or English valence electron concentration , VEC) is the number of valence electrons per atom. This size is the decisive criterion for the question of the possible connections with covalent connections (8-N rule, i.e. that an element of the N. main group 8-N forms covalent bonds) or with ion crystals (noble gas shell for ions corresponds to VEK = 4).
The VEK is also important in intermetallic phases . The problem when considering the VEK is the number of valence electrons , which is immediately clear for many metals (e.g. VEK (Na) = 1, VEK (Mg) = 2, VEK (Al) = 3) many other metals can also depend on the binding partner (see subgroup elements ). The 3d metals are particularly tricky, in which the participation of the d orbitals in the metals and alloys fluctuates very strongly.
The VEK determines the composition of the Hume-Rothery phases . For example, you can calculate CuZn or AgCd from:
- ,
where VE is the valence electron number and the atomic number .
This results in the following relationships for the various phases:
| phase | relationship |
|---|---|
| α ≈ | 21:15 |
| β = | 21:14 |
| γ = | 21:13 |
| ε = | 21:12 |
literature
- Erwin Riedel, Christoph Janiak: Inorganic Chemistry. 8th edition, De Gruyter 2011, ISBN 978-3-11-022566-2 , pp. 200-204.