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Aristotle

340

Believed there were four elements and four qualities, and they would align and be at rest.

Democritus

Jan 1, 1000

Democritus stated that all things are made up of atoms, which are indivisible and indestructable.

John Dalton

Jan 1, 1800

Dalton's theory was that every element was made up of different atoms, specifically with different masses.

J.J. Thompson

Jan 1, 1897

Thomson used a cathode ray tube to inferr that there are small particles inside of every atom. This inference proved dalton's theory to be wrong. Particles can be divided

Henri Becquerel

Jan 1, 1903

Bacquerel discovered that rays emitted by uranium could not be detected by electric or magnetic fields.

Marie and Pierre Curie

Jan 1, 1903

discovered radioactivity with Bacquerel

Ernest Rutherford

Jan 1, 1908

Won the Nobel Prize for Physics in 1908 for his orbital theory of the atom through his discovery of Rutherford scattering off the nucleus with his gold foil experiment

Robert Millikin

Jan 1, 1909

Millikan figured out how to get an electrons mass by doing a famous experiment with Thomson.

Neil Bohr

Jan 1, 1913

Bohr applied the quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits. This led to the calculation of energy levels.

James Chadwick

Jan 1, 1932

Chadwick discovered the neutron.

Quantum Model

Jan 1, 2009

Each electron is thought of as a cloud, of negative charge, instead of one tiny negative particle. It is beleived in this model that electrons "occupy" all of the space in an atom at different levels or rings. An atom consists of energy levels, neutrons, and protons.