ABSTRACT
Recall that an atom is the smallest unit that has the properties of the element concerned. The atom is composed of a nucleus containing the protons and neutrons; surrounding the nucleus are the electrons. I use the word 'surrounding' rather than 'orbiting' as orbits imply nicely spherical or elliptical trajectories. Quantum mechanics (Chapter 1 1) , which is our best description of matter on the atomic stale, tells us the probability of finding an electron about the nucleus but it does not describe well-defined electron trajectories. The probability mapping of an electron about a nucleus may in some instances have a spherical symmetry, but this does not mean that the actual electron trajectory is spherical. It means that we have a higher probability of finding the electron on the spherical shell than some distance away from it. Quantum mechanics doesn't say where specifically on the shell the electron is, so we can't follow it's motion, and we cannot draw trajectories.
