Wednesday, March 23, 2011

Conversations with Henry: Nodal Theory

Henry: The electrons in hydrogen and helium are easiest to depict -- they stay in simple spherical orbitals surrounding the kernel. There are no nodes.

Me: What are nodes?

Henry: In physics, a node is a point of minimum displacement in a periodic system, for example in a vibrating string:

The first harmonic (fundamental) has no nodes, except for the stationary ends. The second harmonic has one additional node in the middle. Nodes correlate with higher energy-- the more nodes, the higher the energy.

Me: How does this relate to electrons?

Henry: Well look at these pictures of how electrons surround a nucleus: Which shape has more nodes?

Me: An s-orbital has no node, a p-orbital has one node, a d-orbital has two nodes, and an f has three?

Henry: Exactly! And that's how electrons order themselves in atoms. It's almost self-assembly. If there's one thing we've learned about electrons it's that they don't flow uphill.

Me: There's got to be exceptions for every rule.

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