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I was thinking about atoms, and then I came up with this: How would an atom visible to the naked eye look? What would be its half life and chemical properties? Could it even exist? Edit: “Seeable”, in this question means be like so you can reliably hold it too. It’s like an atom being the size of a blueberry of marble.

11111
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  • What do you mean by "an atom visible to the naked eye"? Plenty of atoms interact with visible light, your eye just doesn't have the capacity to resolve them individually. Do you mean how large an atom would have to be so you could see it e.g. under a microscope? – KarimAED Nov 09 '23 at 15:35
  • Yes, but so that the nucleus is visible and it looks distinguished from another atoms. Eg, being the size of a marble. – 11111 Nov 09 '23 at 15:37
  • This is really not about atoms, but about the smallest object that a human eye can see. I suggests asking specifically about it (after doing some prior research via Google.) – Roger V. Nov 09 '23 at 15:59
  • @RogerV. no, this isn't about limitationos of the human eye. The question asks what it asks: if an atom were to be the size of a blueberry, how would it look. It actually makes a lot of sense to me, if we suppose that the charge of the nucleus is so huge that the outermost shell has a noticeable probability density at a radius on the order of a centimeter. – Ruslan Nov 09 '23 at 16:07
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    @Ruslan that's your interpretation of what the OP means - legitimate, but not the only one possible. In fact, I recommended closing as needing more focus. – Roger V. Nov 09 '23 at 16:10
  • The (effective) radius of an atom is much larger than the radius of its nucleus, on the order of 100,000 times. That is, if the nucleus was 1 cm, the atom would be 1 km. – PM 2Ring Nov 09 '23 at 16:14
  • for an atom to be visible like a blueberry is, it would have to be the size of a .... blueberry. – JEB Nov 09 '23 at 16:59

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Thanks for your question. Interestingly, the size of the atom doesn't really matter to whether we could see it. Instead, it's the strength of the atom's interaction with light that matters, and this is something that can be engineered by the environment where the atom is. So, it's not strictly a property intrinsic to the atom.

For example, consider graphene (the one-atom-thick sheet of carbon atoms). A sheet of graphene suspended in vacuum would absorb a couple percent of the visible light, and thus it would be pretty hard to see with the naked eye. However, if you put it on a suitably prepared substrate, the interference of light between the graphene and substrate can enhance light absorption to well over 10%, which is clearly visible. The same kind of engineering could be possible for a smaller system of a few or even one atom (although more work would need to go into enhancing the light interaction).

In addition, it is possible for a person to see a single photon of light. Many atoms (that actually exist) can be contrived to emit light in the visible range, and some in green, which is where our eyes are most sensitive. Of course, for a single atom, the light will come out a single photon at a time, but it would be possible to see this in dark conditions with odds better than pure guessing. This question discusses an example of a visible single atom.

Gilbert
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  • The size of the atom is, among other factors, governed by the number of electrons it has (which depends on nuclear charge). If it has so huge number of electrons to have the size of a blueberry, i.e. that the outermost electron shell has noticeable probability density at a radius on the order of a centimeter, such atom may scatter light very noticeably, so as to be visible as a somewhat dense physical object, maybe even optically denser than a sheet of graphene. – Ruslan Nov 09 '23 at 16:10
  • @Ruslan, yes it may scatter light noticeably, or it may not. One would need to calculate the matrix elements, and I’m not confident that physical size is a reliable analog. And since we’re talking about atoms, it would be strongly wavelength dependent. – Gilbert Nov 09 '23 at 18:38