-
Period: 494 BCE to 404 BCE
Democritus
Came up with the idea of two things in the universe: atoms and voids. Atoms were solid and infinite in number and shape and differing in size. All atoms were floating around the infinite void. -
Period: to
J.J. Thomson
1904 suggested model was a sphere of positive matter where electrons were positioned by electrostatic forces. Worked to estimate the number of electrons in an atom. -
Period: to
Ernest Rutherford
Discovered that atoms have a small charged nucleus surrounded by lots of empty space, circled by tiny electrons. Credited with the discovery of the proton in 1919 and hypothesized the existence of the neutron.