DeBroglie hypothesis

The deBroglie hypothesis stated that the electron has both particlelike and wavelike properties. 

Werner Heisenberg, a German physicist, building on deBroglie s hypothesis, argued that it would be impossible to exactly specify the location of a particle (such as the electron) because of its wavelike character (a wave travels indefinitely in space in contrast to a particle that has fixed dimensions). This hypothesis in turn led to the Heisenberg uncertainty principle (1927), which states that it is impossible to specify both the location and the momentum (momentum is the product of mass and velocity) of an electron in an atom at the same time. 

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