Beryllium atom. Computer-digitised illustration of a single atom of Beryllium. This is a typical traditional diagram of atomic structure, showing electrons orbiting around a central nucleus. Beryllium contains four electrons, and a nucleus which has four protons and five neutrons (unseen). The number of electrically positive protons balance the number of negative electrons. This image is highly schematic, as it is now thought that electron orbits are more eccentric and they inhabit a probability cloud" rather than moving in well-defined circular orbits (often called the Bohr model)."