Atoms, Molecules, and Matter Democritus ~ 450 B.C. – argued that by cutting up a piece of matter with sharpest knife imaginable, would eventually come to a piece that would not be cut any further: Atom = (Greek word – indivisible) Idea rejected by Plato and Aristotle – matter is continuous. Due to their influence, Democritus Theory was left dormant for 20 centuries.
Pierre Gassendi ( ) Italian supported by Newton 1600’s: suggests the existence of atoms John Dalton ( ) English chemist and school teacher Developed several laws of chemistry using atomic theory Atoms join to form molecules
Robert Brown ( ) Scottish botanist 1827: looked at pollen grains (suspended in water) under microscope – Browian Motion Explained by Einstein (collision and momentum problem) Dmitri Mendeleev ( ) Period table (only 63 elements) –Period = rows –Groups = columns (elements that had similar properties = families)