Atomic orbit refers to describing the wave-like behavior of electrons in atoms with mathematical functions. This wave function can be used to calculate the probability of finding electrons in atoms in a specific space outside the nucleus and point out the possible position of electrons in three-dimensional space.

Orbit refers to the region where electrons are more likely to appear in the outer space of the nucleus under the definition of wave function. Specifically, atomic orbit is the possible quantum state of a single electron among many electrons surrounding an atom, which is described by orbital wave function.

Electronic configuration of atomic orbital;

The motion of electrons in atomic orbits follows three basic theorems: the lowest energy principle, Pauli incompatibility principle and Hunder's law. The principle of minimum energy means that when electrons outside the nucleus move, they always occupy the orbit with lower energy first, so that the whole system is in the lowest energy state.

On the basis of summarizing many facts, physicist Pauli proposed that two identical fermions could not have the same quantum physical state at the same time. The application of Pauli exclusion principle to electron configuration can be expressed as follows: the same orbit can accommodate at most two electrons with opposite spins.