I tried a few times, and on the second load of the page I got a single hydrogen atom, so I think it's safe to say they aren't excluding things.
There was recently a link, I think on the front page here, to an article about how many chemical compounds there are [1]. Based on that link we're looking at probably trillions to quadrillions of potential structures with atomic weight under 300, which would cover the structures I saw in my few reloads of the page.
Chemistry is wild. For an example close to home, taking table sugar (sucrose, a single type of molecule) and applying heat to caramelize it results in hundreds to thousands of different end products from at least half a dozen qualitatively different classes of chemical reactions.
I never got far enough in chemistry to really figure out if it has explanatory or predictive power.
If you ask a CS grad "What will happen if you run this program?" they should be able to predict it. If they've gone through nand2tetris they can explain it all the way -- compiler, OS, machine language, ALU / registers / bus, logic gates.
If you ask a chemistry grad "What happens when you apply heat to this molecule?" can they predict it? Can you explain it all the way -- from molecules to atoms to electrons to quantum fields?
If we can't predict "Okay this is what will happen if I mix these two substances together," how do we have a good scientific theory? I guess chemistry says we always end up with the same atoms we started with (unless you start to go nuclear by using energetic particles to modify the nucleus), but can we predict which of the zillions of possible rearrangements will actually happen? We know by experiment that H2SO4 is an acid, and that H2SO4 is a "legal" molecule in a way that HSO3 or H5S7O9 are not. Is there a way to figure this out from first principles? Can you figure out by inspecting the chemical formula that H2SO4 will be an acid if you didn't already know that ahead of time? Can you figure out that H2SO4 will be a "legal" molecule but H5S7O9 will not? Can you look at a reaction and tell whether it will "compile" and what it does, the same way you can look at a program and figure out if it will compile and what it does? If you can't, why not?
And what use is a theory of chemistry that can't make concrete predictions? If you just have a list of known substances and reactions, is that even a theory, or is it just experimental data?
> Can you figure out by inspecting the chemical formula that H2SO4 will be an acid if you didn't already know that ahead of time?
Strictly speaking, the answer is "no", because it's not the formula that matters but the shape. And something like C₆H₁₂O₆ doesn't tell you how all of the bonds hook up--are we looking at esters, alcohols, ketones, aldehydes, carboxylic acids? There's several distinct molecules that have that formula, and those distinctions matter for chemistry.
But given the actual structure of the compound? Yeah, we can compute a lot of stuff. That list of words that probably meant nothing to you--that's different kinds of functional groups, and functional groups tend to react in very similar ways when given several compounds. And organic compound is basically all about identifying these groups and the ways in which they react.
> Is there a way to figure this out from first principles?
"First principles" in this case would basically be a large dose of molecular orbital theory, derived from quantum mechanics. And yes, we can develop a good deal of explanations by recourse to molecular orbital--for example, why aromatic and antiaromatic compounds exist, despite the fact they superficially look like the same structure.
> Can you look at a reaction and tell whether it will "compile" and what it does, the same way you can look at a program and figure out if it will compile and what it does? If you can't, why not?
Typically, the difficulty is in figuring out how selective reactions are. If you've got a molecule with a couple different C=C bonds in it, and you're doing an addition reaction across those bonds, predicting how many of those bonds, and which ones specifically, change in the reaction is more of a crapshoot. So it's not foolproof, but it is generally reliable enough at this point that organic synthesis has moved from "here's a Nobel Prize for figuring how to synthesize vitamin B12" to "congratulations on being hired; why don't you synthesize this molecule while we ramp you up on the job."
Computational chemistry answers some of these questions.
When you look at just a molecule by itself “what happens if you apply heat” is somewhat simple. Covalent bonds just break because the molecule is vibrating too much - think of a covalent bond as a flexible strut, if you put too much pressure on it, it snaps. This can result in the temporary formation of unstable molecules that then recombine. You could predict which particular bonds in a molecule are unstable based on the total structure, angles, electronegativity, polarity, etc.
But of course those small unstable molecules can further breakdown, react with each other, and react with the parent molecule to form new stuff. So basically the parent molecule is part of some huge “power set” of potential molecules all interacting with each other.
There was recently a link, I think on the front page here, to an article about how many chemical compounds there are [1]. Based on that link we're looking at probably trillions to quadrillions of potential structures with atomic weight under 300, which would cover the structures I saw in my few reloads of the page.
Chemistry is wild. For an example close to home, taking table sugar (sucrose, a single type of molecule) and applying heat to caramelize it results in hundreds to thousands of different end products from at least half a dozen qualitatively different classes of chemical reactions.
[1] https://www.chemistryworld.com/opinion/chemical-space-is-big...