• 370

# Democritus

First proposed the existence of an ultimate particle. Used the word "atomos" to describe this particle. (370 B.C.)
• # John Dalton

proposed the Law of Multiple Proportions. This law led to the proposal of the Atomic Theory in 1803. He also developed the concept of the mole and proposed a system of symbols to represent atoms of different elements. Came up with the formula for water
• # Solid Sphere model

created by John Dalton
• # J.J. Thomson

Discovered the electron
• # Earnest Rutherford

Studied radiations emitted from uranium and thorium and named them alpha and beta. And using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil. He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.
• # Albert Einstein

Published the equation E=mc^2
• # Plum Pudding Model

Created by J.J. Tomson
• # Robert Millikan

Discovered the unit charge for an electron with his oil drop experiment at the University of Chicago. Determined e = 1.60 x 10^-19 coulombs
• # Nuclear Model

created by Rutherford
• # Niels Bohr

assumied that electrons travel in stationary orbits defined by their angular momentum. This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit.
• # Planetary Model

created by Bohr
• # Werner Heisenberg

He calculated the behavior of electrons, and subatomic particles that also make up an atom.
• # Wolfgang Pauli

Devolped his own principle. According to the principle two electrons in an atomic structure can never have all four quantum numbers in common. If one electron in an atom assumes a state described by all four quantum numbers, then this state is occupied
• # Erwin Schrödinger

used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom.
• # Modern Model

Electrons are in constant motion around the nucleus, protons and neutrons jiggle within the nucleus, and quarks jiggle within the protons and neutrons.
• # Louis de Broglie

Devolped the wave mechanics theory. He believed that electrons can act like both particles and waves, just like light.