Aether is the domain of the immaterial things; it is where the stars reside and the media where all the energy waves move. Aether elementals excel in manipulating the dimensions and electricity; most of the creatures they generate are immaterial.
I agree with dominator that the element should be aether. Yes, it doesn't matter whether or not an atom is
invisible to us, but whether or not it is
immaterial to humans. Today, with all of our technology, we know all about atoms and - to some extent - present them as material things, but as just humans atoms truly are immaterial. Without our technology atoms can be described as nothing else BUT immaterial.