[Skiznibbler]

In chemistry when talking about electron orbitals what does a node mean? For example when talking about a 2s orbital is it the space in between the 2s orbital and 1s orbital?

Heres what it says in the book im reading.

   An electron in a 1s atomic orbital can be anywhere within the 1s sphere, but a 2s atom-
ic orbital has a region where the probability of finding an electron falls to zero. This is
called a node, or, more precisely—since the absence of electron density is at one set dis-
tance from nucleus—a radial node. So a 2s electron can be found anywhere within the
2s sphere—including the region of space defined by the 1s sphere—except in the node.

If the 2s electrons can't be found in the node where exactly is this node located?

[Rabn]

you ever eat a gobstopper? well, I always but them in half and check 'em out. Basically the node is like the center 3 or 4 layers out from the center(nucleus) The reason it can't go there is because: 1) the nucleus is there and 2) because the electrons in the 1s sphere block it.  Think about those electrons wizzing around in all kinds of convaluted ways, the 1s electrons have their place, and the 2s have theirs. there is overlap of course but a 2s electroan can only penetrate so far into the 1s shell before the like charges of the 1s electron push it out.

[Yggdrasil]

Try this experiment.  Tie one end of a jump rope to a chair and hold the opposite end.  Wave around the opposite end to generate standing waves in the jump rope.  Notice that certain points in the wave don't move.  They always have zero amplitude.  So, you will never see the wave at these points (since the amplitude is always zero), even though the wave must pass through these points (since you can see the wave on either side of the node).

[Skiznibbler]

Thanks for the answers. I think I have the idea but I'm not positive. Are you saying the nodes are actually inside the nucleus? You say the outer electrons can't access the nodes because the core(1s) electrons are blocking them. Can the core electrons enter the nodes? I examined that picture but I'm not too sure how that corresponds with orbitals. Is the node just that tiny point in the center of the nucleus where the orbitals expand out from? For example the very tip of the p orbital where it begins inside the nucleus.

[Yggdrasil]

The nodes are regions of the orbital that can be located at the nucleus, but can also be outside the nucleus.  Nodes occur basically because of the destructive interference between the standing wavefunctions of electrons (remember that electrons have wave-like properties).  Note that the diagram I posted does not correspond to the an orbital, it is just a diagram to explain how nodes result from standing waves.

The following page has some visuals to help describe what the nodes in the various electron orbitals look like.  If you have any questions about the page, let us know.

http://www.humboldt.edu/~rap1/Chem_resrc/AOSup.htm