Atomic Model Timeline

Plato

440 BCE

Discovered solid forms of matter are composed of indivisible elements shaped like triangles.

Democritus

400 BCE

Discovered that atoms were uniform, solid, hard, incompressible, and indestructible and moved in infinite numbers through space until stopped.

The Alchemists

600

The Alchemists believed that all metals were formed from 2 principles, mercury and sulfur

Robert Boyle

1659

Discovered that everything was composed of very tiny particles.

Antoine Lavoisier

1789

Discovered that matter was composed of atoms that were not created or destroyed during chemical reactions.

Billiard Ball Model/Daltons Model

1803

Defined an atom to be a ball-like structure as the concepts of the atomic nucleus and electrons were unknown at the time.

John Dalton

1804

Discovered that all matter is made up of atoms and all atoms of a given element are identical in mass and properties. Also discovered that compounds are 2 or more different types of atoms.

Amedeo Avogadro

1811

Equal volumes of gases at the same temperature an pressure contain the same number of molecules regardless of their chemical nature.

Dmitri Mendeleev

1869

Discovered that elements arranged according to the value of their atomic weights present a clear periodicity of properties.

JJ Thomson

1897

All atoms contain tiny negatively charged subatomic particles called electrons.

Solar System Model

1897

Describes atoms as consisting of a nucleus with a number of electrons in orbits around the nucleus.

Pierre and Marie Curie

1898

Discovered that the powerful rays, or energy the polonium and radium gave off were actually particles from tiny atoms that were disintegrating inside the elements.

Plum Pudding Model

1904

Describes an atom as a negatively-charged electrons embedded within a positively charged soup.

Albert Einstein

1905

Mathematically proved the existence of atoms and that any liquid is made up of molecules. Also proved that these molecules are always in a random, ceaseless motion.

Robert Millikan

1910

Proved that electrons have a fixed measurable charge that does not vary and calculate the mass of a single electron

Ernest Rutherford

1911

Described the atom as having a tiny, dense, and positively charged core called the nucleus.

Henry G. J. Moseley

1913

Discovered that the square root of the frequency of the X-Ray emitted by an atom is proportional to it's atomic number

Neils Bohr

1913

Proposed a theory for the hydrogen atom that all electrons move around the nucleus

Werner Heisenberg

1925

Formulated a type of quantum mechanics based on matrices.

Erwin Schrödinger

1926

Discovered that the behavior of electrons within atoms could be explained by treating them mathematically as matter waves.

Electron Cloud Model

1926

Shows a particular area in which an electron is likely to be

James Chadwick

1932

Discovered that the atoms were not only made up of protons and electrons, but there were also neutrons.