You can never say where an electron is at any given moment. You can only state the probability that an electron can be found in a particular region in space given the energy of the electron.Electrons occupy particular energy levels called shells. Electron shells surround the nucleus and are given principal quantum numbers n=1,2,3,4,5,6 and 7 with shell n=1 being closest to the nucleus and having the least amount of energy.The number of electrons in any shell is given by 2n2 where n is the number of the shellThe first shell holds up to 2 electrons.The second shell holds up to 8 electrons.The third shell holds up to 18 electrons.Electron diagrams can be drawn for any element.