Atomic Theory Timeline Project


Democritus of Adbera

460 BC - 370 BC

Proposed that sharp atoms created an acute taste, as well as smooth atoms creating a sweet taste. Theorized that atoms were: indivisible, space exists between atoms, atoms cannot be destroyed, have continual motion, and that there are an infinite number and type of atoms, which differ in shape and size.


384 BC - 324 BC

Aristotle disagreed with the idea that atoms could stay in perpetual motion so he developed a theory of the atom based on the four elements and the activity between each element. Aristotle’s atom was comprised of fire, water, Earth, and air; with in between representing coldness, wetness, dryness, and hotness.


Alchemists are similar to mid evil pharmacists, an alchemist attempts to turn a simpler metal into a metal of a greater worth such as silver or gold. The alchemists would sell things such as longevity potions in terms of medicine.

time of alchemy

1200 - 1700


Isaac Newton

25 December 1642 - 20 March 1727

In 1704 Isaac proposed a theory of a mechanical universe with small solid masses all in continual motion.

Ben Franklin

January 17, 1706 - April 17, 1790

Ben’s famous kite flight in 1752 led him to believe that matter had charges represented by positive and negative.

Antoine Lavoisier

August 26, 1743 - May 8, 1794

“Father of modern chemistry” Antoine stated the first law of conservation of mass in 1789. He also wrote the first extensive list of elements .

Joseph proust

September 26, 1754 - July 5, 1826

in 1797 he created the law of definite proportions stating: a chemical compound always contains exactly the same proportion of elements by mass. His law forms the basics of stoichiometry.

John Dalton

September 6, 1766 - July 27, 1844

Researched the spontaneous disintegration of radioactive elements into variants he named isotopes and used his research to determine each radioactive element’s half-life. He is credited for discovering the atom in 1803.

Michael Faraday

22 September 1791 - 25 August 1867

Studied the effect of electricity of solutions discovered electrolysis as the method of splitting molecules using electricity in 1832. He then made laws of electrolysis based on his studies post 1832.

Julius Plücker

16 July 1801 - 22 May 1868

Built the first functioning cathode ray used to theorize that atomic particles each contained certain charges in 1859.

Johann Jakob Balmer

May 1, 1825 - March 12, 1898

Developed an empirical formula in 1885 for the visible spectral lines of the hydrogen atom which would soon help Bohr create his model.

James Clerk Maxwell

13 June 1831 - 5 November 1879

Maxwell demonstrated that electric and magnetic fields travel through space in the form of waves at the speed of light in 1865. He later used this demonstration to propose that electric and magnetic fields filled the void between atoms emptiness.

William Crookes

June 17, 1832 - April 4, 1919

Upon studying cathode rays in 1879 he made four important revelations: particles travel in straight lines from the cathode, place a negative charge on the objects they impact, and electron particles are deflected by electric fields and magnets to suggest the electrons have a negative charge

Dmitri Mendeleev

February 8, 1834 - February 2, 1907

In 1869, he organized elements into seven groups based on elemental properties. Periodic law he created suggested that elemental properties "were periodic functions of their atomic weights.”

Eugen Goldstein

September 5, 1850 - December 25, 1930

Performed studies on anode rays as well as credited for their discovery, sometimes credited as the discoverer of the proton. Termed canal rays in 1868.

Henry Becquerel

December 15, 1852 - August 25, 1908

Amongst his studies of the effect of x-rays on film in 1896, he discovered some chemicals spontaneously decompose and give off very penetrating rays.

Joseph John Thomson

18 December 1856 - 30 August 1940

Credited with the finding of electons and isotopes, as well as inventing the mass spectrometer. Awarded nobel peace prize for discovery of atom in 1906.

James Larmor

11 July 1857 - 19 May 1942

Larmor studied matter and more specifically the electron theory of matter. Larmor predicted the phenomenon of time dilation for orbiting electrons, and verified that the FitzGerald-Lorentz contraction (length contraction) occurs in bodies whose atoms were held together by electromagnetic forces as of 1897.

Max Planck

April 23, 1858 - October 4, 1947

In 1900, Max used the idea of quanta (specific units of energy) to explain the appearance of heated objects based on the visible spectrum they give off.

Marie and Pierre Curie

15 May 1859 - 19 April 1906

Upon studying the decaying process of Uranium and thorium, they discovered radioactivity in 1898.

Hantaro Nagaoka

August 15, 1865 - December 11, 1950

Influenced by J.J Thompon’s model, Hantoro theorized that J.J was wrong in his work. Hantoro theorized and developed a model (Saturnian model, early plum pudding model) in 1904 that illustrated that opposite charges were impenetrable.

Robert Milikan

March 22, 1868 - December 19, 1953

Oil drop experiment was used to discover the charge and mass of an electron in 1909.

Ernest Rutherford

30 August 1871 - 19 October 1937

1911 Rutherford model challenged Thomson’s plum pudding model by theorizing that the atom was comprised with mostly empty space.

James Jeans

11 September 1877 - 16 September 1946

A mathmaticion, James came up with an equation used to solve for the radius of an interstellar cloud, later to be perfected and used in atoms to study the radius of an atomic cloud in 1928. The equation solves for the critical mass a cloud must attain before being able to collapse.

Lise Meitner

7 November 1878 - 27 October 1968

In 1917, she discovered the first long-lived isotope of the element protactinium. Part of a team that discovered nuclear fission.

Otto Hahn

8 March 1879 - 28 July 1968

Regarded to as the father of nuclear chemistry, worked to discover radioactive elements such as thorium, as well as the first to recognize the uranium atom in 1938. Elements he discovered would later be used in the study of nuclear fission in the atomic bomb.

Albert Einstein

March 14, 1879 - April 18, 1955

Namely famous for his equation E=MC2 Einstein disapproved of the idea of quantum mechanics and was against many of Bohr’s theories. His equation illustrated the amount of energy stored in a certain amount of matter.

Niels Bohr

October 7, 1885 - November 18, 1962

Bohr created the Bohr model in which an atomic nucleus was centered with electrons orbiting around it in 1913.

Erwin Schrodinger

August 12, 1887 - January 4, 1961

Proposed that instead of electrons being stationed amongst orbitals, that electrons behaved more in the matter of an electron cloud. Defined as, “The region of space that surrounds a nucleus in which two electrons may randomly move.”

James Chadwick

October 20, 1891 - July 24, 1974

Credited for the discovery of the neutron in 1932, James theorized the neutron exists to stabilize the atom.

Louis de Broglie

August 15, 1892 - March 19, 1987

Discovered that electrons behaved like waves under certain conditions leading chemists to believe that the atom is not like the solar system and its electrons have no specific orbit.

William Conrad Roentgen

28 Oct 1895

William first discovered x-rays while working with cathode ray tubes. He then discovered that x rays could pass through solid objects, which would be used in Rutherford's experiment to conclude that an atom is comprised of mostly empty space.

Werner Heisenberg

December 5, 1901 - February 1, 1976

Heisenberg is known as the creator of the Uncertainty Principle stating that the exact location and energy of an electron cannot be determined simultaneously. i.e to create an experiment, all experimental objects cannot be the same (stirring rod changes temperature of hot solution slightly from being at room temp.)

Ernest Marsden

1 Nov 1909

Ernest discovered the atomic nucleus by furthering the Rutherford experiment and locating its existence.

Henry Moseley

1 November 1913

Henry Moseley provided the first experimental evidence for Neil Bohr's model by observing X-ray spectra and their wavelengths.

Wolfgang Pauli


Wolfgang discovered the Pauli exclusion principle stating that what he called fermions, were parts of an atom that would not occupy the same space, while so called bossons, were parts of an atom that would occupy the same space.

Robert J Vandergraaf


Robert created the first particle accelerator, named the Van de Graf generator, more modern machines are used today on top of modern technology to provide more answers about the atom.

Enrico Fermi


In 1942, Enrico released energy from the atoms nucleus creating the first controlled chain reaction.