Werner Heisenberg
Heisenberg was a German scientist who is known as the founder of quantum mechanics.
The Uncertainty Principle
Heisenberg proposed his famous Uncertainty Principle in 1927. It said that the more precisely we know the position of an electron, the less precisely we know that electron's momentum, and vice versa.
This means that one can never know the exact location of an electron!
It is because of Heisenberg that scientists use probabilities to describe the location of electrons in an atom.