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I'm not sure if this is a silly question, but I was sitting here with a cup full of cheezey poof balls thinking, "My goodness, it's like an amazing cheesey delicious liquid - huge water molecules!"

Of course my next thought was, "Wait a minute - water has two hydrogen atoms bonded to an oxygen, so that's not quite right. They wouldn't be round like this."

Then I started thinking about the diagrams we see in chemistry textbooks, etc., and how the atoms are always pictured as round balls. How do we know this is accurate? Is it possible for the atoms to be configured in more complicated shapes (e.g. not solid, crystalline, some type of lattice)?

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...delicious? –  haneefmubarak Mar 28 at 18:11

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It depends how you define the surface of an atom, atoms have no surfaces have only regions of space where you have more chances to find electrons. So in fact it is not right saying that they have a true shape at all.

Shapes of Atomic Orbitals

However if you plot the regions where you have the higher probability of finding electron of an atom you can obtain something like this:

enter image description here

These are the shapes of the first five atomic orbitals: 1s, 2s, 2px, 2py, and 2pz from Wikipedia. 1s orbital is sphere shaped but others orbitals have more complex shapes so atoms with many electrons have orbitals very different from a sphere.

Shapes of Molecular Orbitals

Molecules have more electrons and so even more orbitals. They can have very strange "shapes". I've calculated for you with GAMESS and Avogadro the LUMO $2b_2$ water's orbital that is one of molecular orbitals of water. This is the result: enter image description here

Shapes of Atomic Constituents

For answering your question in the comment in fact even protons, neutrons and electrons don't have a real shape due to the wave-particle duality. However we can assume in many cases that neutrons are particles (so we suppose a spherical symmetry) but the de Broglie hypothesis state that they have also a wavelength!

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Same thing for neutrons? –  Wayne Werner Mar 28 at 14:50
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Man... particles are weird. Would it be safe to say that really we don't actually know what makes up "stuff" (i.e. matter) - we just have really good evidence of how it behaves in different conditions? –  Wayne Werner Mar 28 at 15:28
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@WayneWerner absolutely! We can describe very well some quantic phenomena and do some accurate prediction, but we are really far from a true understand of matter! Sometimes science give us the illusion of true Knowledge but in fact it give us only instruments for controls matter! –  G M Mar 28 at 15:36
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All full shells of isolated atoms are spherically symmetric. And, yes, this is not obvious from the visualization images you have selected, but it is clear in the math. –  dmckee Mar 29 at 4:21
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@NicolauSakerNeto why is it limited to half filled or filled? For a free atom, say hydrogen in a 2p state, is the electron in a particular p orbital or a superposition of all three p orbitals? –  DavePhD Dec 3 at 16:15

If you can find a single atom in vacuum with a net dipole moment, its electron cloud is obviously not spherically symmetric. Go across the periodic table's second row. They are all $\ce{1s^2}$ $\ce{2s^2}$, so their atomic cores absent chemical combination and hybridization are first order spherically symmetric, filled s-orbitals.

B $\ce{2p^1}$, C $\ce{2p^2}$, N $\ce{2p^3}$, O $\ce{2p^4}$, F $\ce{2p^5}$, Ne $\ce{2p^6}$

There are three orthogonal 2p oribtals shaped like dumbbells: $\ce{2p_{x}}$, $\ce{2p_{y}}$, $\ce{2p_{z}}$. Maximum multiplicity says they each fill before electron paring occurs, One then suspects B, C, O, and F single atoms in vacuum would have dipole moments. If they superpose orbital hybridization absent chemical combination, symmetry says they do not have a dipole moment. Do they? Google/Google Scholar are your friends.

http://arxiv.org/ftp/arxiv/papers/1010/1010.2425.pdf
For alkali metals. Is the vacuum phase spontaneously dimeric? http://home.physics.wisc.edu/~tgwalker/056.singlet_PRA.pdf
Complicated.

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Firstly, the probablity function for a 2px has the symmetry of a cylinder (a plane of symmetry perpendicular to an infinite-fold rotational axis of symmetry like O=C=O), so a dipole moment would not result. Secondly, for B, C, O, and F single atoms in vacuum the three p orbitals would be degenerate and the electrons would not occupy a particular subset, but an linear combination of all. Finally, there is much interest in looking for permament electric dipoles in atoms due to time reversal violation implications; I would be skeptical of any article that is not peer reviewed. –  DavePhD Dec 9 at 21:10

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