Atomic Theory Timeline

Aristotle

350

Aristotle completely disagrees with Democritus's atom ttheory, instead proposing that everything was made of four elements: Earth, Air, Fire, and Water.

Democritus

465

Democritus hyoithesises that everything on Earth is made of tiny atoms, and that atoms cannot be broken down into anything smaller. This was the precursor to modern atomic theory.

Antoine Lovoisier

Oct 27, 1772

Lavoisier composed the first true list of elements. He also stated that matter itself is impossible to create or destroy. He hypothesised that matter simply just rearranges itself.

Joseph Louis Proust

Jan 1, 1794

Proust created The law of definite proportons, in which the proportions of particles in a compound are the same. The law of definite proportions applies to the weight and mass of a substance. Proust's law later influenced Dalton and his atomic theory.

John Dalton

Jan 1, 1803

John Dalton proposed the atomic theory that stated that all atoms cannot be broken down or changed, tand that atoms of different elements have different weights and masses. He also stated that atoms are impossible to destroy. HIs theory led to the modern atomic ttheory of today.

Dalton/Democritus model.

Jan 1, 1803

This model was believed to be a round, solid sphere.

Michael Faraday

Oct 31, 1831

Faraday worked extensively with electricity. His work with electromagnetics paved the way for electricity being used as an energy source.

Henri Becquerel

Oct 31, 1896

Henri Becquerel discovered Uranium. the first radiactive element that was discovered. He worked closely with Marie and Pierre Curie on radiation. Becquerel is widely known for discovering radiation, opening a door for mew discoveres. He has an SI unit named in his honor.

JJ Thomson

Jan 1, 1897

J.J. Thomson discovered the electron by studying electricity in a vacuum. He is also known for devising the "Plum pudding" model, which theorized that electrons amd protoms being scattered all pver the atom.

Marie Curie

Oct 31, 1898

Marie Curie is known for he work with radiation. She worked with Henri Becquerel when he discovered radiation. Madame Curie also worked with X-Rays and studied potential use of X-Rays in medicine. She also measured the strength of radiation in Uranium Radium was also first discovered by her.

Ernest Rutherford

Oct 31, 1899

Rutherford discovered Alpha and Beta Radiation. He also hypothesised that radiation was the slow decay of a substance over time. Rutherford also worked with Niels Bohr on \the Bohr atomic model.

Plum Pidding model

Oct 1, 1904

J.J. Thomson's model of the atom. in which the atom is a sphere in which neutrons and electrons are scattered across it, almost like a chocalate chip cookie.

Albert Einstein

Oct 31, 1905

Einstein is best known for the theory of releativity. He made contributions to the atomic theory by being able to prove the existence of atoms and subatomic particles. He also came up with the photolectric efect, that says that light is both a wave and a particle.

Niels Bohr

Aug 31, 1913

Bohr is best known for the Bohr model, a model of the atom in which electrond orbit the nucleus like a planet orbits the sun. He was also a prominent scientist who worked on the Manhattan Project.

Robert Milikan

Oct 31, 1915

Milikan worked with electricity on the atomic level. and he worked with electrons. He also studied cosmic radiation. and determined the charges actual overall charge of electrons.

Max Planck

Jan 1, 1920

Founder of Quantum physics at the atomic level. Quantum theory is the modern field of physics we see today. Planck also worked with the physics of radiation and founded a new set of units used in physics, all named after him.

Erwin Schrodinger

Oct 31, 1926

Schrodinger created the electron cloud model, in which the location of electrons is never certain. Because of that, the electrons are in a "cloud" around the nucleus. and never in a fixed location. He also is a major contributor to Quantum physics.

James Chadwick

Oct 31, 1932

James Chadwick discovered the neutron. which changed perception of the atom. His discovery changed the current model of the Atom. since he proved that the neutron is in the nucleus along with protons. Chadwick also worked on the Manhattan Project to create the first atomic bomb.

Otto Hahn

Oct 31, 1938

One of the scientists who discovered the idea of nuclesr fission, which is the splitting of an atom to release energy, He was strongly against the use of nuclear weapons.

Lisa Meitner

Feb 11, 1939

Lisa Meitner was one of the first people to use nuclear fission. Nuclear fission is when an atom is split apart, giving off tremendous amounts of energy.

Louis DeBroglie

Oct 31, 1940

De Broglie heavily worked on Wave-mechanics and quantum theory. He proved that electrons have wavelength properties, and hypothesised that all matter has wavelengths.

Glenn T Seaborh

Jan 1, 1942

Seaborg discovered new radioactive elements, such as plutonium. His work influenced the Manhattan Project. He also was an advisor to several US presidents.