Atomic Model Timeline

Democritus

442 BCE

Democritus created Democritus' Atomic Theory, which stated that everything is composed of atoms.

Plato

427 BCE

Introduced theory in which ideal geometric forms serve as atoms.

The Alchemists

500

Preformed experiments in which the goal was to change the structure of metals and ores to increase their value. Created a scientific process which would lead to discovery of the atom.

Robert Boyle

1662

Created Boyle's law, which stated that atoms must exist based on the relationship between the pressure and volume of gas.

Antoine Lavoisier

1772

Discovered the role oxygen plays in combustion. Named oxygen(1778), and hydrogen(1783).

John Dalton

1803

Created Dalton's Atomic Theory, which was the first complete attempt to describe all matter in terms of atoms and their properties.

Billiard Ball Model

1803

Created by John Dalton He envisioned atoms as solid hard spheres, like billiard balls, so he used wooden balls with holes to model atoms.

Amedeo Avogadro

1811

Created Avogadro's law, which corrected a problem with Dalton's theory. He made it possible to accurately estimate the atomic masses of elements and made a clear distinction between atoms and molecules.

Dmitri Mendeleev

1869

Created what we know today as the periodic table.

J.J. Thomson

1897

Discovered subatomic particles during experiments with cathode ray deflection.

Pierre and Marie Curie

1903

Deduced that radioactivity does not depend on how atoms are arranged into molecules, but rather that it originates within the atoms themselves.

Plum Pudding Model

1904

Created by J.J. Thomson. Model tried to account for 2 properties of atoms known at the time. Includes electrons surrounded by a volume of positive charge.

Albert Einstein

1905

Created Brownian Motion, which proved the existence of atoms.

Robert Millikan

1910

Using the oil-drop experiment, he created a way to measure an electron's charge accurately.

Ernest Rutherford

1911

His theory of the atomic nucleus proposed that most of the atom's mass is concentrated in a small, dense nucleus consisting of protons and neutrons.

Solar System Model

1911

Created by Ernest Rutherford. Also known as Rutherford model. Describes an atom as a tiny, dense, positively charged nucleus, in which nearly all the mass is concentrated, surrounded by light, negatively charged electrons that circulate at some distance, much like planets revolving around the sun.

Niels Bohr

1913

Contributed to the atomic model. He was the first to discover that electrons travel in separate orbits around the nucleus. Also discovered that the number of electrons determines the properties of elements.

Henry G. J. Moseley

1913

Discovered that each element contains a unique positive charge. Asserted that the periodic table should be arranged in order of increasing atomic number.

Electron Cloud Model

1926

Created by Erwin Schrodinger and greatly contributed to by Werner Heisenberg. Says that we cannot know exactly where an electron is at any given time, but the electrons are more likely to be in specific areas.

Erwin Schrodinger

1926

Introduced the first discovery of wave equation for electron movements.

Werner Heisenberg

1927

Formulated quantum mechanics in terms of matrices. Also discovered the uncertainty principle, which states that a particle's position and momentum cannot both be known exactly.

James Chadwick

1932

Discovered neutrons using the polonium-beryllium-paraffin experiment.