I know that I learned in Chemistry class that a bond is defined to be ionic if the electronegativity difference between the atoms is more then 1.7, half the electronegativity difference between the most electronegative element fluorine and the least electronegative element francium. I think I heard that there's no clear definable distinction between a covalent bond and an ionic bond. I'm not sure it's the case that we can't define one. I believe we could define it by whether there is a localized electron pair at each bond. I know aluminum and oxygen have an electronegativity difference of more than 1.7. However, one web page said Corundum was a covalent network. Then I checked for myself and saw that corundum indeed probably does satisfy my definition of a covalent network. I know that sulfur can hybridize to make 6 covalent bonds with fluorine. Theoretically, could have a substance that's like corundum with the sulfur atoms instead of aluminum atoms and carbon atoms instead of oxygen atoms. Here we would say the sulfur hybridized to form 6 covalent bonds and the carbon is forming the usual 4. I know coordinate covalent bonds are possible also. If that substance could exist as a covalent network with a localized electron pair at each bond, why couldn't it also be a covalent network with a localized electron pair at each bond when you have aluminum and oxygen instead? It's still the exact same total number of protons per unit cell.
My question is
Has it already been researched whether corundum has a localized electron pair at each bond between an aluminum atom and an oxygen atom?
I know it's not completely clear but my questions was written the best way I can possible write it with my abilities and my lack of expertise in quantum mechanics. I can't figure out given how quantum mechanics works what my question would be, and I don't want to use my time on studying quantum mechanics. Maybe even if I did know how quantum mechanics worked, I would still be unable to figure an algorithm for determining what type of answer would satisfy me. When somebody is working on a complicated project that uses a lot of thinking, they can't figure out an algorithmic plan on how they will react to every situation. Rather, they trust themself to use their discretion later on what ever situation arises. A good answer would come from an expert who can function as if they are a future self of me and is good at hunting down existing research that they would use their discretion that they can write an answer about that has a good chance of satisfying me. As long as they write it in a way I can see as a good answer and see why it can be considered one, I think it will satisfy me.
As described in my question Can replacing some of the atoms in a covalent network with that of the element one atomic number higher make it nonstick?, maybe researchers will use an answer to that question to invest in new research. Then if they're going to invest in that research, then an answer to this question that corundum indeed does have a localized electron pair at each bond might further help them incorporate this idea into that idea and add corundum to the list of potential substances that can be treated that way to gain those revolutionary properties. Corundum will have the additional property that it can't combust. Maybe they will make hard highly nonstick nondegradable frying pans out of treated corundum.