In the quantum mechanical solution of the Schroedinger equation for electronic wave function of an atom, it is (correctly) assumed that the probability distribution function for the electron, Psi(r, theta, phi) is the product of three distribution functions: R(r), f(theta)and g(phi). The g(phi) function has a simple solution, exp(+/- im*phi), where m is an integer related to the electron's orbital angular momentum. The functions R(r) and f(theta) are called the radial and angular wave functions, respectively.
