Energy Band in solids

[logearav]

Revered Members

Considering isolated Lithium atom which has 3 electrons, K shell will have 2 electrons with energy -13.6eV. L shell will have 1 electron with energy -3.4eV. Now , considering a small piece of Lithium metal containing 100 atoms, then there would be 100 K levels and 100 L levels differing in energy by extremely small amounts. We call it as energy band.

Why there is small change in energy when there is energy band, while there is no energy change for isolated atoms?

Edited November 17, 2011 by logearav

[questionposter]

Revered Members

Considering isolated Lithium atom which has 3 electrons, K shell will have 2 electrons with energy -13.6eV. L shell will have 1 electron with energy -3.4eV. Now , considering a small piece of Lithium metal containing 100 atoms, then there would be 100 K levels and 100 L levels differing in energy by extremely small amounts. We call it as energy band.

Why there is small change in energy when there is energy band, while there is no energy change for isolated atoms?

 

Probably because you can't really measure a single atom. Maybe with super advanced instruments that were developed really recently you can, but the energy change of 1 atom is kind of hard to measure.

[DrRocket]

..., while there is no energy change for isolated atoms?

 

Change from what ?

[swansont]

Chemical bonds will shift energy levels, and the banding is the result of the Pauli exclusion principle. Electrons can be distinguished by which atom they belong to in an individual atom.

[questionposter]

Chemical bonds will shift energy levels, and the banding is the result of the Pauli exclusion principle. Electrons can be distinguished by which atom they belong to in an individual atom.

 

Wait what? Why would you need to use a combined wave function if you can distinguish between individual electrons per location in an atom?

[John Cuthber]

Probably because you can't really measure a single atom. Maybe with super advanced instruments that were developed really recently you can, but the energy change of 1 atom is kind of hard to measure.

What we can measure doesn't affect what exists.

Lithium atoms had energy levels before there were people to wonder about them.

 

Also it is, in a sense, perfectly simple to measure individual atoms.

If you look at the yellow light from an old street light through a spectroscope you will see that almost all the light is one of two wavelengths.

That's because the light is emitted by single atoms.

Each photon of light was emitted by just one atom. If you put a little effort into the measurement you can count the photons individually and measure their energy. That tells you about the energy states of individual atoms in the lamp. You can even get some information about how fast it was going.

[swansont]

Wait what? Why would you need to use a combined wave function if you can distinguish between individual electrons per location in an atom?

 

You don't.

 

You get banding in solid-state materials where the electrons are shared, owing to the Pauli exclusion principle. The Pauli exclusion principle doesn't come into play for two separate atoms.

[Widdekind]

Is there a relation, between 'banding', and 'electron degeneracy pressure', e.g. in WDs (both being due to the PXP) ?