The History of the Atom

Democritus [460 BC]

▣ Named tiny bits of stuff atomos - “uncuttable”

▣ Did not do any experiments

For MANY MANY Years…

ALCHEMY!

John Dalton [1803]

Developed The Atomic Theory1. All matter is made of

particles called atoms2. Atoms of the same

element are identical3. Compounds are made

of 2 or more elements 4. Elements combine in a

fixed ratio to create compounds

JJ Thomson [1897]

▣ Discovered the electron during his cathode ray tube experiment

▣ Model: Plum Pudding Model (or the Chocolate Chip Cookie Dough Model) with a positively-charged cloud of “dough” and negatively-charged interspersed “chips”

Ernest Rutherford [1907]

▣ One of Thomson’s students!▣ Is credited with discovering that

atoms are mostly empty space using a gold foil experiment

▣ Model: Planetary Model

Niels Bohr [1913]

▣ Won Nobel Prize in 1922▣ Determined that

electrons have energy levels by studying light patterns

▣ Electrons can jump from level to level - jumping away from the nucleus requires the electron to absorb energy, falling towards the nucleus will cause the electron to emit energy (light)

Erwin Schrödinger [1926]

▣ Tried to support Bohr’s model with math

▣ Noticed that electrons sometimes acted like waves

▣ BIRTH OF QUANTUM MECHANICS

Other notable events:

▣ The Periodic Table was organized by Dmitri Mendeleev in 1869

▣ Marie Curie studied radioactivity in 1898▣ Louis de Broglie proposed that electrons have a

wave/particle duality in 1923▣ Neutron discovered by James Chadwick in 1932▣ Enrico Fermi created the first man-made

nuclear reactor in 1942