How did Einstein contribute to atomic theory?

In 1905, Albert Einstein published an analysis in which he devised a mathematical way to predict the size of both atoms and molecules. At the time, the science of atoms was still in its infancy, but Einstein's test was crucial in leading the way towards testing the reality of atoms.

In addition to predicting atomic size, 1905 was the year that Einstein released his specialized theory of relativity as well as several other papers that were invaluable to the expansion of physics and chemistry. In the same year, Einstein also accurately calculated both the diameter of a sugar molecule and Avogadro's number.