Atomic Theory Timeline

Events

Empedocles

0492 BC

Empedocles was the first to propose that four elements that made up everything: earth, wind ,water, and fire. His work later inspired Aristotle.

Democritus

400 BC

Democritus was the first person to developed the theory of the atom. His work has been lost and only fragments of his work remain.

Aristotle

0322 BC

Aristotle did not believe in Democritus's atom theory. He believed that all materials on earth were made up of earth, wind, water and fire.

Antoine Lavoisier

1794

Antoine Lavoisier discovered that mass is retained when it undergoes a chemical reaction. His work led to the law of the law of conservation of matter

John Dalton

1803

John Dalton proposes his atomic theory. The two of his four points in his theory argued that all atoms are indestructible and invisible and a chemical reaction is a rearrangement of atoms.

j.j Thomson

1897

J.J. Thomson discovered the electron and the proton. He then developed the plum pudding model

Albert Einstein

1905

Albert Einstein treated energy and matter as the same. This thought process would become known as the theory of relativity

Robert Millikan

1909

Robert Millikan's oil drop experiment help discover more about the electron. This data helped all future scientist understand the atomic structure.

Marie Curie

1911

Marie Curie studied uranium and thorium and called their decay radioactivity. She also discovered elements of polonium and radium

Ernest Rutherford

1911

Ernest Rutherford discovered that have a charged nucleus and a space in the middle orbited by electrons. He then came up with the Rutherford

Niels Bohr

1913

Niels Bohr discovered that there are energy levels for certain electrons. He said that electrons move only in a set orbits

Max Planck

1918

Max Planck devoloped the the quantum theory. This helped scientist understand atoms better

Louise De Broglie

1924

Louise De Broglie did research on quantum physicist. He discovered the wave nature of electrons.

Ernest Schrodinger

1926

Ernest. Schrodinger created the electron cloud model. It was dense nucleus surrounded by a cloud of electrons

James Chadwick

1932

James Chadwick discovered the neutrons are in the center of the atom. They have the same mass as a proton.