Atomic Theory Timeline

Democritus (460 BC) Democritus proposed the idea of atomic theory, which stated the universe was made up of atoms and the space they move in.

Aristotle (384 BC) Aristotle did not believe in atomic theory, he believed that everything was made of four elements: Fire, Earth, Water, and Air

Alchemists (400-1400) Alchemists had the goal to take a basic element such as lead and turn it into a precious medal such as gold

Leucippos (~400 BC) Leucippos came up with the theory of Atomism, which stated everything is made up of small particles which arrange to create all things in the physical world

Paracelsus (1493) Paracelsus was one of the first to use chemicals and minerals in medicine

Amedeo Avogadro (1776) Avogadro theorized that two gasses in a space of equal volume have the same amount of molecules provided they are at the same temperature and pressure

Henri Becquerel (1852) Becquerel discovered radioactivity through experiments with uranium

Jöns Jacob Berzelius (1779) Berzelius created the law of constant proportions which states that elements in inorganic substances are bound together buy definite proportions by weight

Niels Bohr (1885) Bohr was the first to discover that electrons travel in separate orbits around the nucleus

Robert Boyle (1627) Boyle discovered that when the pressure of a gas is increased the volume shrinks in a predictable way

William Crookes (1832) Crookes discovered the element Thallium and invented the Crookes Tube

John Dalton (1776) Dalton's atomic theory stated that all matter is made from atoms and compounds are made from two or more different types of atoms

Joseph Louis Gay-Lussac (1778) Gay-Lussac is most know for his discovery that water is one part hydrogen and two parts oxygen

Werner Heisenberg (1901) Heisenberg developed the "uncertainty principle" which said it is impossible to know the precise speed or location of something.

Friedrich Hund (1896) Hund introduced the method of using molecular orbitals to determine the chemical bond formation of molecules

Antoine Lavoisier (1743) Lavoisier proposed the Combustion Theory which states mass is conserved through combustion

Robert Andrews Millikan (1868) Millikan discovered the charge of an electron through the "Oil Drop Experiment"

Henry Gwyn Jeffreys Moseley (1887) Moseley studied the atomic structure through a process called X-ray spectra

J.J. Thomson (1856) Thomson discovered electrons and discovered atoms have a positively charged core and negatively charged particles

Georg Ernst Stahl (1659) Stahl was the originator of the phlogiston theory which states phlogiston is released during combustion

Erwin Schrödinger (1887) Schrödinger discovered the quantum mechanical model of the atom using mathematical equations to describe the likelihood of finding an electron in a certain position

Carl Wilhelm Scheele (1742) Scheele discovered the elements Oxygen, Chlorine, Molybdenum, and Barium

Ernest Rutherford (1871) Rutherford proved Thomson atomic model to be wrong using the famous gold foil experiment, he demonstrated the atom has a small dense nucleus

Joseph Proust (1754) Proust discovered the law that any compound the elements are present in a fixed proportion by weight

Joseph Priestley (1733) Priestley discovered a handful of gasses including oxygen and nitrous oxide

Max Planck (1858) Planck was the originator of quantum theory

Wolfgang Pauli (1900) Pauli discovered the Pauli exclusion principle which stated no two electrons can occupy the same quantum state simultaneously