To me both the band gap and first ionisation energy seems to be the same thing as both are the energy required to remove the valence electron from the atom. So I am confused whether they b are the same thing referred to by different names in physics and chemistry . I searched on the internet but I couldn't find any convincing answer. So my question is what is the difference between band gap and first ionisation energy? Are they the same thing? Please explain in detail and I have just recently started studying these things so please use layman's terms .
$\begingroup$
$\endgroup$
Add a comment
|
2 Answers
$\begingroup$
$\endgroup$
Ionisation energy is typically measured for free atoms in a gaseous state. Atoms in a solid crystal lattice behave differently from atoms in a gas state. In particular, the electronic energy levels are modified, so that there are states available where the electrons are still 'bound' to the atomic lattice, but free to move within the lattice. This is the conduction band.
If an electron in the conduction band absorbs even more energy (greater than the 'work function'), it can indeed fully free itself from the atoms; the crystal lattice is now ionised.
Fig 1 in this article shows the relationship between these various bands.
$\begingroup$
$\endgroup$
They are very different concepts.
If you have an atom and try to give it enough energy so that one electron is knocked out of the orbital, the minimum amount of energy required is the ionization energy.
When talking about a band gap, you should be thinking about a crystal, which is made up of many many atoms put together periodically in a lattice. Examples of them are metal or insulator or semiconductor.
It turns our that, in the language ofquantum mechanics, each atom donate several orbitals, which are connected to orbitals of neighboring atoms. All these orbitals get mixed together and form a "big molecule" with eigenenergies from each orbital closely packed within a finite energy interval. These closely packed eigenenergies are called bands. Different orbital form different bands, and these bands describe the collective property of the crystal. The band gap describe the energy required to put one electron from a lower band to a higher band. Especially, it describes the energy differnce between the cunduction band and valence band, you can look up their definitions.
If you want to know more about bands, pick up a book or lecture on solid state physics.
