I recently asked this about why we call things "isotopes" and "elements" (atoms) instead of just having it be a bunch of particles bundled together in different numbers.

This makes me wonder about the definition of Chemical, which Wikipedia has sort of a circular definition. A chemical cannot be broken into elements (atoms) unless breaking chemical bonds (basically the definition)....

So atoms have protons and neutrons (and electrons) that are bound by "atomic bonds". I'm not sure that's correct. So strong force holds a single together. But not sure what holds protons together, maybe that's the weak force. Then "chemical bonds" are between electrons between atoms. My question is, why not just get rid of the distinction of calling things "protons vs. atoms vs. chemicals", and just say there are "particles" which bundle together. They bundle into group 1 (atoms), and group 1's bundle into group 2's (chemicals), but really it's all just particles that are all interacting.

So this makes me wonder, what exactly a chemical is. It is a stable particle system essentially, where atoms combine into larger chunks.

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    $\begingroup$ See, as soon as you got rid of "atoms" and "chemicals", you came up with your own "group 1" and "group 2". There is no going around it. This level of organization just is there, and you need a word for it. Other terms are too broad. Come to think of it, you are a stable group of atoms combined into larger chunks. $\endgroup$ – Ivan Neretin Jun 4 '19 at 5:00
  • $\begingroup$ Chemicals is a kind of practical and commercial definition. Products that one can buy. Are Mg flakes or Fe shavings to be called chemicals? Probably, as they are listed in catalogues. Surely they aren't atoms nor fine chemicals. The definition of Wikipedia is wrong, and refers instead to molecular compounds, or even elements as they normally come as chemicals, if bonds such as the metallic one are considered. Wikipedia and this SE page seem to confuse chemicals and compounds. Thiugh the two terms aren't mutually exclusive, as it should be clear from what I said above, they refer to.... $\endgroup$ – Alchimista Jun 4 '19 at 10:18
  • $\begingroup$ . to different contests and uses. You pass an order to buy chemicals, not atoms or elements or molecules.... Do you get it? $\endgroup$ – Alchimista Jun 4 '19 at 10:22
  • $\begingroup$ I see your question - and not Wikipedia - MIXES chemicals with chemical substances. The latter being elements or compounds.. You should change titles and text else you are asking a different thing for which my comments hold. $\endgroup$ – Alchimista Jun 4 '19 at 10:44

The distinctions matter because of what we can observe in nature and the lab

If you want to make sense of the world around you it helps to have some coherent scheme to describe the world and classify the things in it. That scheme should map onto things we can observe. We could just describe things by their nuclear properties (the count of protons and neutrons in the atoms) but this is a poor classification for two reasons:

  • things with the same number of protons are very, very similar and it mostly doesn't help to distinguish them unless you are doing nuclear physics
  • most of the substances we observe in the world have properties that their nuclear composition does not explain

We have a periodic table not a (much bigger) nucleonic table because the easily observable properties of elements (which are mostly chemical or physical unless you are a nuclear scientist) are very similar for isotopes with the same number of protons. Most of the ways those "particles" interact are highly dependent on which element they are.

We have a separate class (chemicals, molecules or chemical substances) because of the way atoms interact. Different atoms join together in different ways the mostly demand on how their electrons are configures (which, in turn, depends on the number of protons in their nucleus). There are bazillions of ways to combine atoms into molecules and each resulting chemical substance has distinct features (colour, melting point, taste, toxicity....) The observable features are dependent on how the atoms join together: different ways of joining them together result in substances with different properties. That's why we have a subject called chemistry. If we ignored that combinatorial complexity and just talked about combinations of particles we would be ignoring the obvious ways of classifying the distinct chemical substances we observe.

It is worth looking at a few examples to clarify this and to explain the Wiki definition of chemical. First note that chemical substance includes elements (everything is a chemical substance even if it is only made from one type of atom). Take carbon, for example. Diamond is one type of carbon, graphite is another. Both are forms of the element (technically allotropes). Both could be thought of as bundles of carbon atoms but that is a useless definition as it doesn't explain why their properties are so different. Chemistry does: they are different because the way the atoms are joined together and organised is different (one has flat hexagons in near-infinite planes, the other has near-infinite tetrahedral arrays of carbons joined together). Or consider ethanol and dimethyl ether. They both contain exactly the same bundle of atoms. But that doesn't explain why they are so different (one boils at -24 Celsius, the other is a pleasant intoxicating drink). again the way the atoms are connected together explains the observable difference in properties; the bundle of atoms they re made from does not.

Moreover, those observable properties of chemicals will be the same even if the atoms they are made from are different isotopes (12C and 13C are very similar and alcohol made form either will still make you drunk and taste like booze). So chemists mostly ignore nuclear properties and explain things using the periodic table which explains almost everything about how atoms connect together into molecules.

So we group different nuclei together into elements because that helps us classify the things that make up chemicals in ways that help explain what matters about how they connect together. We have a separate classification for chemical substances as they depend on the details of how atoms connect together. These are meaningful classifications that help us explains the properties we can observe in the world and the lab.

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In theory you could go one step further, and describe things only by a Waveform a. la. quantum mechanics. If you did this, you could do away with all distinctions completely, and merely have one waveform which describes the entire system!

The reasons for the different categories are practical ones. If I'm talking at what we now call the atomic level, working with small numbers of atoms, I hardly care about the precise configuration of where the protons and neutrons are in the nucleus. What I'm doing is almost always completely immune to changes at that level. Thus, why waste my time looking into such small details.

I also typically don't have much control over the lower levels. Unless I am working at a nuclear reactor, or looking into how the sun works, the number of protons and neutrons in an atom is pretty much fixed. There's radioactivity, which sort of dabbles between them, but other than those cases, I treat the number of subatomic particles as pretty darn fixed.

Likewise, when it comes to chemicals, they have behaviors which are very reliable. In particular, we can predict how one chemical turns into another. If I have acetic acid and sodium bicarbonate (aka vinegar and baking soda), I can reliably predict what will happen when I combine them, without worrying about precisely how the atoms are vibrating within their general shape, nor care about the isotopic mixtures.

If you really think about it, the whole thing is rather arbitrary because it's focused around bonding. Nothing in the laws of physics causes bonds to "form" and "break" like we claim they do. Rather these are simplifications of much more complicated interactions. But for all intents and purposes, it is incredibly effective to think in these terms.

So why do we have chemicals, atoms, and protons? Because generations of scientists have found that if you choose to think in those terms, you find things behave very predictably, and if you choose other lines to draw, they are much harder to predict. It's the human mind that put those divisions there, not nature.

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  • $\begingroup$ I think you went a bit too much. Chemicals is just a word to refer to chemical products available for further chemical use what ever they are. Like reactives might be chemicals or made from chemicals, and like reagents can be chemicals to be used in further reactions. All practical "definitions" with little physics in it. $\endgroup$ – Alchimista Jun 4 '19 at 10:28
  • $\begingroup$ After I found out that the OP assumed chemicals as chemical substances. So all my comments were dictated by this. Still my comment is valid . Not to start sterile polemics but the answer is vague and mentions non necessary hard stuff. Which is not a surprise as for the question itself doesn't help a potential answerer. $\endgroup$ – Alchimista Jun 4 '19 at 10:55
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    $\begingroup$ @Alchimista I read the question as more of a philosophical one of why put divisions in place at all. If the question just mentioned chemicals and atoms, I think you would be right, but when protons get into the mix, I think that shows more of a fundamental "how does science approach these problems" sort of thing. $\endgroup$ – Cort Ammon Jun 4 '19 at 14:54
  • $\begingroup$ Yes you're right. Indeed the question is a bit displacing. Also, though chemicals has its own meaning, it is still true that all chemicals are chemical substances, after all. $\endgroup$ – Alchimista Jun 5 '19 at 9:17

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