To avatar!: It's been a while, but I thought electrons were defined by four quantum numbers, including energy level (n), angular momentum (l), azimuth (m sub l) and spin (m sub s). The Pauli exclusion principle then stated that no two electrons can have the same set of quantum numbers in an atom or molecular bond.
To Jodo Kast: From what I recall from my QM classes, when you start to get into higher vibrational/rotational states for molecular bonds, the difference between energy levels of successive states collapses to essentially nothing, producing a continuum of energy levels. At temperatures that we're accustomed to on Earth, everything is in a fairly high translational/rotational/vibrational state, so from an energy perspective, we can have continuity.
I definitely disagree that numbers are imaginary. The number four is very real, and I can give a very good physical representation of the presence of fourness; I can have four coconuts, for example, or four rabbits' feet. Even so-called imaginary numbers have very real applications in the real world (they make dealing with periodic functions a whole lot easier).
Here's a question to you: suppose that you consider only the set of rational numbers. Is it continuous? Or is it discountinuous? You could claim that it is discontinuous because it leaves out all the irrational numbers, but you can approximate any irrational number with a rational number with arbitrary precision (e.g., even though pi is not rational, I can come up with a rational approximation of pi that is correct to the 80,000,000th decimal place). What about the set of all algebraic numbers? Is it discontinuous because it leaves out all the transcendental numbers? And is the set of transcendental numbers not continuous because it doesn't contain zero?
In my mind, continuity depends on both what you are measuring, and what you are using to measure it. If you say that an atomic monolayer is continuous because there are no atoms missing from their predicted spots, fine. If you say that the monolayer is discontinuous because one of the electrons is out of place, then you are imposing a necessary degree of precision upon this monolayer, and you should reference it as such. As avatar! said, you need to choose a frame of reference.