Today is the birthday of Henry Moseley, born in 1887, he developed the concept of an atomic number, which led to the modern arrangement of the elements on the periodic table, were elements are sorted by the number of protons or atomic number. Before this the elements on the periodic table were organized by atomic mass. Moseley died as a common foot soldier during World War I at the age of 27.
Johannes D. Van der Waals was born on this day in 1837. He is known for Van der Waals forces that describe the behavior of gases and their condensation to liquid phase due to the forces between molecules. He is also known for van der Waals radii.