Democritus/Leuccippos 400 BC Greek philosophers Matter is composed of atoms; between atoms lies empty space “Atomos” – in Greek means uncuttable Indivisible atoms Atoms always will be, in motion

Aristotle Greek Philosopher All matter composed of the four elements: Earth Fire Air Water He was wrong, but b/c he was well respected his idea was trusted over Democritus.

John Dalton Designed the ‘Billiard Ball Model’ Atoms are solid sphere shapes Matter is made tiny indivisible particles called atoms, which cannot be destroyed. Each element is made of unique atoms and cannot transform to become other elements. All atoms of an element are the same but different from atoms of other elements. Elements combine in whole number ratios with other elements to form compounds

John Dalton Limitations: Did not know about subatomic particles Did not know about nuclear reactions Did not know about isotopes

J.J. Thomson Designed the Plum Pudding Model Atom contains negative and positive charges suspended throughout. Cathode Ray Tube experiment: Discovered the electron Theory that the electrons are suspended throughout the atom and help in place by an opposite charged area. Predict the electrons contain the atoms mass Agrees the atom is mostly empty space.

J.J. Thomson Limitations: Did not know placement of particles. Believed the electrons contained the mass of the atom

Rutherford Created the Nuclear Model Gold Foil Experiment Limitations: Discovered the “nucleus” small, dense, positively charged center of the atom Proved the atom was mostly empty space. Electrons were moving around the nucleus of the atom Limitations: Could not explain the electron paths

Neils Bohr Created the Planetary Model Electrons orbit the nucleus in “fixed” orbits They can jump up a level when energy is added Light is emitted as the electron goes back down to the ground state

James Chadwick Previously worked with Rutherford in looking at subatomic particles Discovered the neutron Neutral with a mass equal to a proton neutron

Louis de Broglie Came up with the idea of wave-particle duality Atoms/particles can act as a wave λ = hv

Heisenberg Uncertainty principle - Impossible to know the exact position and velocity of an object (electron) simultaneously The more accurate you measure one property, the less accurate the other becomes

Schrodinger Quantum Model Electron cloud model Orbital – where you will most likely find an electron Electrons are in constant motion Electron cloud model Accepted today

Millikan Discovered the charge of an electron and the mass of it as well using the Oil Drop experiment balancing gravitational force with the upward buoyant and electric forces on tiny droplets of oil suspended between two metal electrodes Also worked with the concept of Photoelectric effect