Chemistry Timeline

Democritus

370 BCE

Experiment - used analogies of his experiments that gave him a picture of atoms and distinguished them by shape, size, and arranged their parts. 4
Discovery - everything is composed of atoms.1
Atomic Model - Knew if something got so small it would be indivisible.6

Dalton

1803

Experiment -
Discovery - Dalton’s Atomic Theory
Elements are made of tiny particles called atoms.
Atoms of an given element have identical mass, size and other properties but, atoms of different element differ in size mass and other properties.
Atoms cannot be created, divided or destroyed.
Atoms of different elements combine in whole number ratios in order to form chemical compounds.
In Chemical reactions atoms are either combined separated rearranged.8

Willian Crookes

1879

Experiment - cathode-ray tubes 9
Discovery - Crookes tubes that created a better vacuum pump that allowed him to produce cathode- ray tubes with a smaller residual gas pressure. 9
Atomic Model - Crookes Tube 7

Erwin Schrodinger

1887

Experiment - likelihood of finding an electron in a certain position.
Discovery - wave equation for electron movements 18
Atomic Model - quantum mechanical model of the atom. 18

Antoine Henri Becquerel

1896

Experiment - using naturally fluorescent minerals to study the properties of x rays 11
Discovery - discovered radioactivity through his investigations of uranium and other substances.5

Atomic Model - phosphorescent elements 12

JJ Thomson

1897

Experiment - channeled a stream of ionized neon through a magnetic and an electric field and used deflection techniques to measure the charge to mass ratio ( mass spectronomy ) 10
Discovery - determined that all matter is made up of tiny particles that are much smaller than atoms 10
Atomic Model - plum pudding model

Marie Curie

1903

Experiment - Her and her husband were “noodling” with crystals and magnetism and they found this element.20
Discovery - Radioactivity; and the elements Polonium and Radium
Atomic Model - Randomly stumbled across it by accident.

R.A. Milikan

1910

Experiment - Oil drop experiment; the velocity of ionized oil drops compared to extremely highly charged charged drops is measured and the highly electrified dops could be suspended on a mechanical equilibrium.18
Discovery - Charges of elements is a constant of physics.18
Atomic Model - Atomic theory and oil drop experiment.

Ernest Rutherford

1911

Experiment - Gold Foil Experiment, shot a beam of alpha particles at a sheet of gold foil, a few of the particles were deflected, concluding that a tiny, dense nucleus was causing the deflections.13

Discovery - atoms have a small charged nucleus surrounded by largely empty space, and are circled by tiny electrons 14

Atomic Model - Planetary, or Rutherford Model

Niels Bohr

1912

Experiment - liquid droplet theory involving nuclear fission
Discovery - electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element. 15
Atomic Model - the atomic model of an atom with a positively charged nuclear and a surrounded by orbiting electrons 15

James Chadwick

1972

Experiment - James Chadwick was assigned the task of tracking down evidence of Rutherford's tightly bound "proton-electron pair" or neutron. 17
Discovery - discovery of the neutron 17
Atomic Model - Modern Atomic Theory