For example, does one atom of gold have a golden color?
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1$\begingroup$ IT depends on the property. Some properties of bulk materials result from interactions among the atoms making up the material (electrical conductivity and colour in metals for example). Other properties are common (atomic number for example). $\endgroup$– matt_blackCommented Feb 3, 2019 at 14:27
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$\begingroup$ There is an interesting caveat about gold however. The reason that gold has a different color than most other metals is in fact an atomic absorption effect, not metallic or electric. Silver has a strong absorption as well but it is in the UV whereas for gold it is in the visible part of the spectrum. See this and this for example. Gold atoms absorb blue light, but they would not have a metallic appearance, that requires that they are in bulk and there are conduction electrons. $\endgroup$– uhohCommented Feb 4, 2019 at 0:50
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1 Answer
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Molecular properties such as melting point, conductivity, elasticity all require a multiplicity of atoms or molecules to be observed since each of those properties are defined interactions between the same particles. Color is different - when a photon hits an atom the atom's electrons are excited, the electron will fall back to it's unexcited (ground) state and when it does it emits a photon. This photon will not always have the same energy as the photon absorbed, when this is the case the rest of the energy was converted into thermodynamic energy (heat). Since the color of a wave of light can be defined by its energy then atoms can have "colors". This is a bit of an oversimplification but I hope it helps!
Edit: as @alchimista pointed out the color of a single atom will not likely represent the color of a sample of that element large enough to see. Also the light reflected from most atoms will likely cover the entire visible spectrum which will result in the same color of light being reflected as was used to illuminate it.
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$\begingroup$ Atoms can have colors all right, but not necessarily the same as the bulk material. $\endgroup$ Commented Feb 3, 2019 at 8:11
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1$\begingroup$ I suggest editing because colour, and specifically for a metal, dramatically depends on the number of atoms bound in the sample. Gold nanoparticles can probably span the entire visible and even the reflectivity should change. It could even be that colour is even more size dependant than, let us say, the melting point of a nanoscale sample. The answer is good just for pointing out the difference between collective and atomic properties but the colour example is misleading. $\endgroup$ Commented Feb 3, 2019 at 9:46
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$\begingroup$ That is also the point where it becomes quite interesting to look at statistical thermodynamics, so the combination of larger amounts of particles with quantum mechanics leading to the classical macroscopic description of many fundamental thermodynamic equations. $\endgroup$ Commented Feb 3, 2019 at 11:19