For example, if you take a sample of human bone and put it under a microscope, how do you know if the atoms you’re seeing are calcium atoms? You can’t exactly count the protons on the inside, can you? Also, how do you distinguish between protons and neutrons? Do they reflect different wavelengths of light and so have different colours or something? I’ve also heard people saying that we can’t actually see atoms using microscopes, is that true? If so, how can we say something is made out, say, carbon, when we can’t see it? If the answer to that is that we have tests (flame tests for metals, precipitate tests, pH tests, etc…), then how did we know it is that element/compound that results in the test turning out a certain way? I have so many questions!
P.S. I know that nuclei aren’t really perfect spherical balls, but rather collections of protons and neutrons, which are spheres, in a classical, non-quantum-mechanical sense.
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They’re not *really* spheres. It’s just convenient to call them that. In reality, the particles are constantly moving around at such a high speed all we can ever really say about where they are is that they are “somewhere within this sphere”.
The way we know what we’re dealing with is the way elements behave when we do things like heat them up or combine them is described by the number of electrons they have, and THAT is most strongly influenced by their number of protons and neutrons. Atoms can carry a charge and be ions, but in general we can do other things to understand if we’re working with ions or not and remove the charge to make them the element they are.
If the numbers of electrons for elements are wildly different than what we expect, we’ll find we can’t make certain reactions work.
That’s how flame tests, precipitate tests, pH tests, etc. work. We’ve spent hundreds of years studying what happens if we do those things to “pure” samples of the element and our model of atoms has a kind of algebra to it that describes the expected results. If we perform an experiment the algebra tells us what we should get, and if we get a different result the only explanation can be “this sample is not made of the element we thought it was”.
A lot of this was done without seeing them, purely using that algebra. A lot of Physics is similar: it uses math to describe the results we’ve observed but we can’t actually see the things the math implies exists even with our best microscopes. This is why sometimes things like Relativity come along and cause a HUGE leap in our knowledge: before Relativity our math for how things move was “good enough” but there were a lot of things going on in the universe we couldn’t explain. Relativity explained almost all of those things and why the math that was “good enough” wasn’t working for them.
So it’s also possible that one day, we might figure out that the whole proton/neutron/electron model is wrong and there’s some other explanation. But maybe not. Right now chemistry has far fewer “we don’t know why this happens” situations than astrophysics or even biology. Those holes in our knowledge represent places that what happens in our experiments is not what our math says should happen. If we don’t have many of those holes, it implies that our math is accurate, which implies the model is close to reality.
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