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It is well known that single atom of oxygen is not stable, and it forms $\ce{O2}$ molecule. But elements like carbon form a network of repeated bonds. As answered in another question, last atoms in such network are unstable and need to create some bonds.

Is it possible to have a (free-standing) single atom of carbon? Stable in the form of a stable powder like graphite or diamond.

If not, what is the minimum size of a carbon particle (diamond or graphite network)?

Further Clarification: I meant normal chemical stability to have a powder material at room temperature. I do not mean highly reactive carbon, quickly turning into a compound.

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    $\begingroup$ You seem to have several questions here. I've answered your question title, but you also ask 1) about carbon specifically and 2) about how much carbon it takes to make a stable molecule. $\endgroup$ – Brilliand Sep 18 '14 at 21:20
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    $\begingroup$ Ultimately, stability has to be determined with respect to something. Helium gas is stable with respect to chemical reactions, but unstable with respect to nuclear fusion (even at 0 K, thanks to quantum tunneling; tremendous pressure and temperature just speed it up). But then all matter as we know it in the Universe is unstable with respect to subatomic particles. All atoms are expected to suffer proton decay (and consequently neutron decay too) over sufficiently long timescales (at least around $~10^{35}\ yr$, but not more than $~10^{200}\ yr$). $\endgroup$ – Nicolau Saker Neto Sep 18 '14 at 22:59
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    $\begingroup$ @NicolauSakerNeto, yes, but it is Chemistry site, so you can safely assume that "stable" means "chemically stable". $\endgroup$ – Wildcat Sep 19 '14 at 7:42
  • $\begingroup$ There are a couple interesting platonic hydrocarbons which are related to buckyballs: en.wikipedia.org/wiki/Platonic_hydrocarbon $\endgroup$ – Peter A. Schneider Sep 19 '14 at 10:55
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Is it possible to have a (free-standing) single atom of carbon?

It's definitely possible, but such an atom would be highly unstable and likely would have a short lifetime. An example of this happening is if you blasted some carbon material with a laser. Here's a really cool paper where researchers blasted carbon nanotubes and graphene with lasers and observed single-atom chains (not an individual atom in this case, but the same principle applies) of carbon exhibiting some very interesting electronic properties:

http://www.pa.msu.edu/cmp/csc/eprint/DT086.pdf

If not, what is the minimum size of a carbon particle (diamond or graphite network)?

Buckyballs (60 carbon atoms) come to mind.

Tangentially related....

A few years ago, a team of Australian scientists fabricated a single-atom transistor (the basic building block of integrated circuits). The atom was Phosphorus. Granted, the atom was not free-standing, but still very impressive. Such a device is extremely difficult to fabricate, and requires cryogenic temperatures, so it's doubtful that this would ever become a viable technology.

http://www.nature.com/nnano/journal/v7/n4/full/nnano.2012.21.html

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Is it possible to have a (free-standing) single atom of carbon?

Yes, it is just the matter of having appropriate physical conditions. So, for instance, atomic carbon exist in the gas phase above 3,642 °C (according to Wikipedia).

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  • $\begingroup$ Well, the OP asked about room temperature, before he dies. $\endgroup$ – Peter A. Schneider Sep 19 '14 at 10:54
  • $\begingroup$ @PeterSchneider, initially there was no restriction on temperature. $\endgroup$ – Wildcat Sep 19 '14 at 11:05
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A single atom of helium is stable in nearly all circumstances. Stability isn't a binary thing, though; whether an atom will react to form a molecule depends on what other atoms are available to react with (for instance, xenon is generally non-reactive, but will form molecules with fluorine), as well as temperature (as Wildcat mentions) and pressure.

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