jan 1, 1926 - Quantum Mechanical Model
Erwin Schrödinger took Bohr's model further and created a model in which the placement of an electron cannot be perfectly defined, but he used a series of equations to detect the probability of the electron. He described his model to be a cloud of probability that surrounds the nucleus; where the cloud is most dense, the more likely it is for an electron to be there.
Added to timeline:
Development and Discovery of Atomic Theory, the Periodic Table, and Radiation