Wave–particle duality is the fact that every elementary particle or quantic entity exhibits the properties of not only particles, but also waves. It addresses the inability of the classical concepts particle or wave to fully describe the behavior of quantum-scale objects.
The electron beam was reflected like a wave, rather than like particles. In other words, they found, as de Broglie had speculated, that wave particle duality is a property not only of light (photons), but of matter as well. Electrons, protons, alpha particles, and anything else that physicists might discover.  We have seen that the essential idea of quantum theory is that matter, fundamentally, exists in a state that is, roughly speaking, a combination of wave and particle-like properties. That adding of waves is the essence of the phenomenon of the interference of waves. The theory of matter waves tells us that particles like electrons are also waves. So we should be able to add several of them together, just as we could add several light waves together. The Anatomy of a Wave. A transverse wave is a wave in which the particles of the medium are displaced in a direction perpendicular to the direction of energy transport. A transverse wave can be created in a rope if the rope is stretched out horizontally and the end is vibrated back-and-forth in a vertical direction. A longitudinal wave is a wave in which the particles of the medium are displaced in a direction parallel to the direction of energy transport. A longitudinal wave can be created in a slinky if the slinky is stretched out horizontally and the end coil is vibrated back-and-forth in a horizontal direction. Mechanical Waves are waves which propagate through a material medium (solid, liquid, or gas) at a wave speed which depends on the elastic and inertial properties of that medium. There are two basic types of wave motion for mechanical waves: longitudinal waves and transverse waves. The animations below demonstrate both types of wave and illustrate the difference between the motion of the wave and the motion of the particles in the medium through which the wave is travelling. De Broglie, in his 1924 PhD thesis, proposed that just as light has both wave-like and particle-like properties, electrons also have wave-like properties. The wavelength, λ, associated with an electron is related to its momentum, p, through the Planck constant, h :  Wave-Particle Duality. Publicized early in the debate about whether light was composed of particles or waves, a wave-particle dual nature soon was found to be characteristic of electrons as well.  Light Is a Wave! (Grimaldi and Huygens). The wave theory, which maintains that light is a wave, was proposed around the same time as Newton's theory. In 1665, Italian physicist Francesco Maria Grimaldi (1618 to 1663) discovered the phenomenon of light diffraction and pointed out that it resembles the behavior of waves. Now that the dual nature of light as both a particle and a wave has been proved, its essential theory was further evolved from electromagnetics into quantum mechanics. Einstein believed light is a particle (photon) and the flow of photons is a wave. Wave–particle duality is the fact that every elementary particle or quantic entity exhibits the properties of not only particles, but also waves. It addresses the inability of the classical concepts particle or wave to fully describe the behavior of quantum-scale objects. As Einstein wrote: . Niels Bohr regarded the duality paradox  as a fundamental or metaphysical fact of nature. A given kind of quantum object, will exhibit sometimes wave, sometimes particle, character, in respectively different physical settings. Interactive Tutorial. Particle and Wave Reflection An excellent comparison of the wave and particle theories involves the differences that occur when light is reflected from a smooth, specular surface, such as a mirror. This interactive tutorial explores how particles and waves behave when reflected from a smooth surface. 
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what properties are particles and waves