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Why the pronoun 'I' is capitalized in English? Is it so because of it being a one-letter word?

That's really good We used to call this activity 'reading around the subject' though nowadays you could call it viewing investigating or whatever. And you are using the chemical vocabulary you are acquiring. 😀 Let's look at the first chemical equation I wrote for you again, but in more detail. Acid + Base = Salt + Water. I didn't mention before that there are many different acids; there are many different bases. The substance that is produced by the acid + base reaction is called a salt. Sodium chloride is also called common salt, but it is just one of many salts that can be produced. Each salt is specific to both the acid and base that react with each other to form the salt. Some salts are water soluble, some are not. The 'or not' is important because it is often useful to find out and eliminate what a sample is not. Silver nitrate is a salt which is water soluble white salt. Silver chloride is a white salt that is not soluble in water. Now you are asking about identification. So an easy first check is to see what it is not i.e. does it dissolve in water ? Well we have seen the result of that experiment so we can se that if the white powder that purports to be silver nitrate dissolves in water it could be correct. But if it does not dissolve the it definitely could not. This kind of thinking is not only important in chemical analysis, but also in geology since it helps determine what substance could or could not be in a given bunch of minerals. It is also important in chemical synthesis - that is finding ways to make a particular chemical substance. Remember our way of making sodium chloride is the Acid + Base = Salt + Water equation or reaction. Hydrochloric acid + Sodium hydroxide = Sodium chloride + Water. But this will not work well for silver to make silver chloride because silver hydroxide is almost insoluble in water. So to make silver nitrate we need a different reaction and obviously with the right acid, this time nitric acid. Here is a short video of how to make silver nitrate by dissolving pure silver in nitric acid (This is an exmaple of an oxidation- reduction or redox reaction already mentioned). I am not suggesting you actually carry it out for safety reasons. After this I think it is time we started putting some flesh on the idea of stuff or matter. As someone with good knowledge of flight and aviation I hope you understand the difference between weight and mass ? If not let us know and we will incorporate that.

I actually did a paper on how the corporate sector was heavily involved/influential in the formation of the United States during my final history course. You bet, from fur traders to ship builders. Nothing brings a people together like business.

Broadly speaking, you are asking how a chemist knows what a given substance is. In the modern day, we have several instruments that provide spectroscopic data that helps identify the structure of a substance. It should be noted that this depends on the purpose of the investigation. For example, if we simply wish to check that the substance is what it is claimed to be, then one can simply compare a spectrum of the unknown with a spectrum of a known sample. The spectrum itself need not provide much information about the structure because all one needs is that the two spectra be the same, like comparing fingerprints. By contrast, if the substance is truly unknown, then one would choose spectroscopic data that provides useful information about the structure. And different instruments provide different information about different aspects of the structure. For example, a low-resolution mass spectrum tells one the molecular mass of the substance. A high-resolution mass spectrum tells one the molecular formula of the substance. A proton nuclear magnetic resonance spectrum provides information about the environment of each hydrogen atom in the molecule, including couplings to adjacent hydrogen atoms. X-ray crystallography provides what is more or less an actual picture of the molecule, including precise bond lengths and bond angles (though this does require a good quality single crystal of the substance, and substantial computer processing of the diffraction data, and may not provide a complete picture). There is of course a lot more that could be said, but I think the above provides a glimpse into the world of the working chemist.

As I see it, the band gap is the minimum energy difference between the bands, whereas the width of the bands themselves can increase the energy difference that is accessible. A 1 eV band gap corresponds to an infrared photon of wavelength 1240 nm, whereas a 4 eV band gap considered to be an insulator corresponds to an ultraviolet photon of wavelength 310 nm. Thus, the band gap of a semiconductor is thermally accessible, whereas the band gap of an insulator is not visibly accessible. I was unable to locate data on band widths, so I can't at present say that the energy difference between the bands admits visible photons. I'm guessing that there is an immediate absorption and lossless reemission that is due to the continuum of energy differences between the bands. This is different to refraction and different to absorption by non-metallic materials. However, I must say that the details are getting somewhat beyond me. Have you ever seen rhodamine B? It forms shiny dark green crystals and a violet solution (and violet smears in trace amounts on a white benchtop). I find this intriguing.