<P> As with all particles, electrons can act as waves . This is called the wave--particle duality and can be demonstrated using the double - slit experiment . </P> <P> The wave - like nature of the electron allows it to pass through two parallel slits simultaneously, rather than just one slit as would be the case for a classical particle . In quantum mechanics, the wave - like property of one particle can be described mathematically as a complex - valued function, the wave function, commonly denoted by the Greek letter psi (ψ). When the absolute value of this function is squared, it gives the probability that a particle will be observed near a location--a probability density . </P> <P> Electrons are identical particles because they cannot be distinguished from each other by their intrinsic physical properties . In quantum mechanics, this means that a pair of interacting electrons must be able to swap positions without an observable change to the state of the system . The wave function of fermions, including electrons, is antisymmetric, meaning that it changes sign when two electrons are swapped; that is, ψ (r, r) = − ψ (r, r), where the variables r and r correspond to the first and second electrons, respectively . Since the absolute value is not changed by a sign swap, this corresponds to equal probabilities . Bosons, such as the photon, have symmetric wave functions instead . </P> <P> In the case of antisymmetry, solutions of the wave equation for interacting electrons result in a zero probability that each pair will occupy the same location or state . This is responsible for the Pauli exclusion principle, which precludes any two electrons from occupying the same quantum state . This principle explains many of the properties of electrons . For example, it causes groups of bound electrons to occupy different orbitals in an atom, rather than all overlapping each other in the same orbit . </P>

The proton has a larger mass and opposite charge as the electron