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Physics, Astronomy & Cosmology / Re: If two four inch cubed elements of glass, and carbon are noncrystalline, why?
« on: 08/01/2016 06:01:20 »Quote
why the carbons electrons are absorbing light, but in the four inch cubed glass the electrons are not absorbing light?Adding to the comments by chiralSPO...
3D Amorphous Carbon in the form of charcoal, or 2D crystalline carbon in the form of graphene is a fairly conductive material. There is a "sea" of electrons which are shared among many atoms.
A consequence of Pauli's Exclusion Principle is that no 2 electrons can share the same energy level. In a material like this, there is not just a single energy level for outer electrons, but a "band" of energies which are shared among all the electrons. This means that no matter what energy a photon has, it will quickly hit an electron with just the right energy to absorb it. This results in a black material (although it takes many layers of graphene to become totally opaque).
However, silicon dioxide in glass is an insulator, each molecule tightly holding onto its own electrons. In this case, the electrons do not see the atoms of adjacent molecules so strongly, and the electron energies are more tightly confined. Silicon Dioxide does not absorb much in the visible range (but it does absorb in parts of the ultraviolet and infra-red spectrum).
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