Wave mechanics is a branch of quantum mechanics developed by Erwin Schrödinger which considers matter in terms of wavelike properties (see wave-particle duality) rather than as systems of particles. Thus an orbital electron is treated as a 3-dimensional system of standing waves represented by a wavefunction. In accordance with the uncertainty principle, it is not possible to pinpoint both the instantaneous position and velocity of the electron; however, the square of the wavefunction yields a measure of the probability that the electron is at given point in space-time. The pattern of such probabilities provides a model for the "shape" of the electron orbital involved. Given wavefunctions can be obtained the Schrödinger wave equation. Usually, and not unsurprisingly, this can only be solved for particular values of the energy of the system concerned. describes the probability density of an object in space and time.