Atomic orbitals are the places surrounding the nucleus of an atom where the electrons are most likely to be at any given time. It is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom.[1]
The number of atomic orbitals in an element is defined by the period the element is in. Electrons move between orbitals depending on how much energy they have and how many other electrons there are.
In atomic theory and quantum mechanics, an atomic orbital is a quantum number. Each such orbital can be occupied by one or two electrons. The way orbitals are arranged is related to the electron configurations of atoms. They were derived from descriptions provided by early spectroscopists of certain alkali metalspectroscopic lines as being sharp, principal, diffuse, and fundamental.[2][3][4][5]