Diamond's hardness is connected to its three-dimensional network of strong carbon-carbon bonds. Krishna Choudhary and Lester Nare describe how each carbon atom bonds to four neighbors, introducing the structure against which hexagonal diamond is compared.
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10:08>> Yeah. >> The reason why it's called a cubic diamond is notice that the repetitive fundamental unit of the crystal is in the shape of a cube, right? >> If you imagine you can take that same cube, put one right next to it, put one right next to it, and stack, and you get bigger and bigger. And the a diamond is going to have, you know, 10 to the 20 of these carbon atoms or something like that. An enormous amount, but at the fundamental scale, that is what the diamond looks like. The reason why it's so hard is each of those bonds are highly tight covalent bonds where the carbon atoms are sharing an electron with the neighboring carbon atom. Remember I said carbons can do four bonds. All four bonds are other carbon
10:48atoms. This thing is extremely tightly packed. >> Mhm. >> Mhm. >> Okay? >> Mhm. >> And it's single bonds that are going in. >> Yes. >> Okay? So, that's the fundamental unit of stacking. It's a cube, hence normal diamond is called a cubic diamond. >> Yeah. >> Right. >> Okay. Now, in 1962,
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