The electron cloud is a way of visualizing the results of mathematical equations used to calculate the position of an electron as it orbits the nucleus of the atom. The area where the cloud is densest describes the most likely location of the electron at a particular point in time.
Scientists use many different models of atoms to understand their behavior and interaction with other materials. The 1913 Bohr model describes the atom as concentric circles of negatively charged electron orbitals surrounding the positively charged nucleus but is unable to explain Erwin Schrödinger's 1926 experimental results from shooting charged particles through a slit in gold foil. The electron cloud model, with electrons able to move through orbitals with characteristic energies and shapes, provides a better fit for experimental data. Schrödinger's equation, with infinitely many solutions, predicts both shape and density of the cloud. The model also takes into account Heisenberg's uncertainty principle. The electron cloud model, as well as Bohr's model, considers atoms as consisting only of positively and negatively charged particles. The 1932 discovery of the neutron led to further refinement of the model. Since 1932, scientists continue to discover additional particles in the atom, leading to changes in atomic descriptions.