Atomic orbitals are the places surrounding the nucleus of an atom where the electrons are most likely to be at any given time. It used to be believed that electrons behaved similarly to the solar system, where the sun is the nucleus and the planets are like the electrons. However, electrons do not go in circles, they move . The number of atomic orbitals in an element is defined by the period the element is in. Electrons move between orbitals depending on how fast they are moving and how many other electrons there are.