Electrons are expressions of probability:)

But, yes they orbits the 'nucleus' of an atom.

they are treated as particles but due to Heisenberg uncertainty principle they are not to be pinpointed.

http://www.bbc.co.uk/dna/h2g2/A408638Also they seem to 'jump' in discrete jumps out/in depending on their energy content.

There is no smooth descent or ascent to them moving around a atoms nucleus.

As for what is the in or outside of an atom?

I suppose the electron sort of define the radius of it but depending on energy-content it as stated 'jumps' between 'valence bands'.

The atom consists of somewhere around 99.999(?) 'empty space'

You can read more about it here

http://particleadventure.org/frameless/atom_fund.htmlAnd here is a 'movie' of an electron.

http://legerdemain.wordpress.com/2008/02/23/electronthe-movie/-------

Virtual particles seems to exist. The reason why we think so is that there are 'interactions' between them and the rest of our spacetimme.

http://en.wikipedia.org/wiki/Virtual_particles#Manifestations Although

" Virtual particles are an artifact of perturbation theory that give an intuitive (but if taken too far, misleading) interpretation for Feynman diagrams. More precisely, a virtual photon, say, is an internal photon line in one of the Feynman diagrams.

But there is nothing real associated with it.

Detectable photons are always real, 'dressed' photons.

Virtual particles and the Feynman diagrams they appear in, are just a visual tool of keeping track of the different terms in a formal expansion of scattering amplitudes into multi-dimensional integrals involving multiple propagators - the momenta of the virtual particles represent the integration variables. They have no meaning at all outside these integrals. They get out of mathematical existence once one changes the formula for computing a scattering amplitude. "

As they are to fast to 'notice' except by their 'interactions' they are allowed 'magical' properties.

Like faster than light (as they might have an 'imaginary mass').