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So in one of the previous videos, we talked about being a theory specifically to explain why medals are very conductive and behavior. And so again, let's recall that band Gap theory essentially uses three idea of molecular orbital theory. And so we think of amongst well for many atoms. And so if we combine all of the atomic orbital's four atoms that are essentially very similar, we can actually create bands instead of discrete energy levels because there are so many of the atomic orbital's that will have very similar energies and will affect each other. But we console some them up, and so we instead have bands instead of these discrete energy levels. And so we can actually use band Gap theory to understand the connectivity of different materials, based on the fact that there is a bank up in between the conduction band and the balance pan. And so let's also remember that the Valence Band is essentially the band where the valence electrons are, and we can also define this as the homo. And so when we studied chemistry, we actually use the term homo and live a lot. And so who will represent the highest occupied molecular orbital. And so, essentially, this is where the electrons will fill up. And so, um, the ho can be thought of as a Beyonce band, because that is again, where the valence electrons will reside when you think of it, in terms of where they are in the molecular, Ordell's that you can possibly have. And let's also define the conduction band. And so the conduction band can be thought of as the limo, which is the lowest occupied like the orbital. And so these are essentially the orbital's that are right above the Homo. And so when you excited the electron, these are the molecular orbital's that they will occupy first. And so when we talk about bang out theory, we talk about these specific bands, and the space in between them is called the Band Gap. And so this is energy gap between De Valence Band was geologist represented Phoebe and Conduction Band, which are represented as See me. And so we'll be using this to define the different types of materials that we have and so we can have medals which are highly productive as well as semiconductor is which are somewhat connective beneath of energy Thio, excite the electrons and we also have insulators, which how poor connectivity and so electrons do not move around freely in. And so when we think about the bankrupt structure for metals, we can actually think, uh, two different versions. And so all of them have some kind of pills, band and silver medals. What's actually represent this as like this black band? Because we have medals. And so we have bands that are filled with electron, and this is the same across the board because all of these structures have molecules and Adams, which have atomic orbital's. And so if you combine them together, we can create molecular Orbital's, and they all have electrons. And so these orbital's must be filled. And so we have all of them have some kind of version of a field band, and we also know that all of them have some kind of empty band or the blue. And so this is actually where you'll see the biggest differences. Um, and so we know that in the case of the metal, we know that they have a the notion man, while the conduction man can actually so close that there is a negligible band gap. We can also have a case where the conduction band is overlapping with the Valence band and so the electrons can move freely. Um, and so this is why medals are conducted in some this case, we have a small band gap, which are a brilliant as Fiji because of space. And so because of the small bank gap, not a lot of energy is required to excite the electrons, which I'll just do in blue. And so, because of the small energy difference and the basically I'm negligible difference in the case of here, we know that the electrons have a pretty easy time moving between the Valence Band and the Connection ban. And so this makes it easy for the electrons to move in the material. And so this makes a lot sense when we think about it in terms of the band back. And as for semiconductors, um, it does have a band gap, but it's still relatively small. And so this band gap is typically about, uh, TV 20. And so there is some energy required to excite the electron to go into this connection ban, but it's still small enough so that it actually becomes an in between between metal antique insulators. And so, in the case of semiconductor, it's not impossible to make it connective. But it is only possible under certain conditions. And when we actually introduced impurities into material, we can actually make it more conductive in some manners. Um, in some instances, and so we'll learn a bit more about that later. But right now we know that semiconductors have a larger band gap than the medals. Um, but a band gap of this size is still, um, large enough to make it not as connected as females. And so for insulators, we actually see a pretty large band gap. And so it's actually hard to excite the electrons. And so it's harder for the electrons to be excited and move around in the material. And so this band gap is actually, um, anything greater than two e. V. In some cases, we can define this as being a TV or more, Um, and so because the band gap is so large, the electrons end up being at the Valence Band for the most part, and it's very hard to have it get excited and occupy the connection band where it can move around in the material. And so again, we can use band Gap theory to understand the differences between the different materials and specifically understand three energetic that come into play when we want to move the electrons inside the material.

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