1. Evolution of the Atomic Theory

2. Greek Philosophy (400 BC) Democritus “All matter is made of atoms” Philosophy is knowledge gained only by observation and logic, not by experiment Story goes like this (story, not fact…) – –Observed boiling water, steam, but then steam disappeared. –After disappearing, reappeared on glass or metal plate above… something invisible is there!

3. John Dalton (1803) Studied gases, found that something invisible had mass and volume… Dalton’s Theory : Atoms are indivisible and indestructible All atoms of the same element are the same Atoms of different elements are different Atoms combine in simple whole number ratios to form compounds Billiard ball

4. J. J. Thomson (1880) Used a cathode ray tube Determined the particles in the cathode ray tube to be a stream of negative particles Determined that the atom is composed of smaller particles Discovered the electron Blueberry muffin model or chocolate chip cookie model, officially the “Plum Pudding model”

5. Robert Millikan (1910) Oil Drop Experiment Determined charge of electrons by suspending a drop of oil between magnets Combined with Thomson’s experiments, was able to determine mass of electron.

6. Ernest Rutherford (1909) Shot alpha particles at gold foilgold

7. Ernest Rutherford (1909) Surprised to find that although most particles traveled straight through the foil, some were deflected Discovered a positive center that he called the nucleus The atom is mostly empty space

8. Niels Bohr (1913) Calculated the line spectrum for hydrogen (go to 39 sec. on video)spectrum Observed different line spectrums for each element Postulated that electrons travel in orbits around the nucleus Bohr-ing

9. Erwin Schrödinger (1926) Used calculus to figure out probability of locating electron. Mathematical graphs displayed “regions of probability” for location of electrons called “ORBITALS”

10. James Chadwick (1932) Bombarded a beryllium atom with alpha particles Discovered that neutrons are in the nucleus p+nop+no

11. Discovery of Proton Somewhere in time, between Rutherford and Chadwick, physicists figured out that the actual particle proton must exist. Rutherford is (kind of) credited with the proton, due to his discovery of the positive nucleus!