Atomic Theory

Democritus

460

Called the particle ‘atomos’. Theorized that we are all made of particles.

Alchemists

500

Alchemists developed a theory that all metal is made up of sulfur and mercury and they believed that any metal could be turned into gold. They spent many years trying to find someone who could turn another metal into gold.

Benjamin Franklin

Jun 13, 1752

KIte experiment led to the discovery that mater has charges.

Antoine Lavoisier

Apr 23, 1777

Classified an element as a simple substance.

Charles Augustine de Coulumb

Apr 23, 1780

Discovered that like forces repel.

Michael Faraday

Apr 23, 1839

Michael Faraday was able to complete a number of experiments using static, batteries, and animal electricity in order to produce electrostatic attraction, electrolysis, and magnetism. He thought that only one electricity existed and differing current and voltage would produce different types of results.

Dmitri Mendelev

Apr 23, 1869

Dmitri Mendeleev had just published the book Principles of Chemistry. He had also published the periodic table with all the known elements and predicted a few in order to complete the table.

Wiliam Crookes

Apr 23, 1895

William Crookes identified the first known sample of Helium.

Henri Becquerel

Apr 23, 1896

Dsicovered radiation by studying X-rays and studying fluoresence.

J. J. Thompson

Apr 23, 1897

Joseph John Thomson continued to investigate and experiment with cathode rays. Through his work he was able to discover the existence of electrons and isotopes. He also came up with his own model of the atom known as the plum pudding model. He thought that an atom was a sea of electrons suspended in positively charged particles.

Ernest Rutherford

Apr 23, 1899

Ernest Rutherford coined the terms alpha ray and beta ray as a way to distinguish the different types of radiation.

Max Planck

Apr 23, 1900

Max Planck presented what is now known as the Planck postulate which states that energy can only be a multiple of an elementary unit of energy. E=hv(nu). h is Planck’s constant and v(nu) is the frequency of the radiation.

John Dalton

Nov 3, 1900

Created concept of ‘mole’.

William Crookes

Apr 23, 1903

William Crookes started to research and experiment with radioactivity. He was able to discover Uranium-X or protactinium.

Pierre and Marie Curie

Apr 23, 1903

: Pierre and Marie Curie were awarded with the Noble Prize, along with Henry Becquerl, for the joint discovery of radioactivity, a term coined by Madame Curie. Pierre and Marie were also able to discovered polonium and radium. They now have a unit of radioactivity named after them called a “curie” (3.7 x 10^10 decays per second).

Albert Einstein

Apr 23, 1905

Albert Einstein published a paper that explained the photoelectric effect which he was later given a Nobel Prize for. The photoelectric effect states that electrons are emitted from substances in any state when they absorb energy from light.

Robert Milikan and Harvey Flecther

Apr 23, 1909

Robert Milikan and Harvey Flecther did the oil drop experiment and were able to calculate the charge of a single electron. Harvey Flecther’s work on this experiment was kept secret until after his own death.

Ernest Rutherford

Apr 23, 1911

Ernest Rutherford completed the gold foil experiment where he discovered the existence of a nucleus and created a new model of the atom, disproving Thomson’s plum pudding model. In the experiment alpha particles were beamed through a very thin sheet of gold foil. Many alpha particles were beamed back which proved that there was a nucleus. His model is also known as the planetary model of the atom.

Niels Bohr

Feb 15, 1913

Explained the spectrum of atomic hydrogen using Rutherford’s research.

Werner Heisenberg

Apr 23, 1925

Created matrix mechanics, the predecessor of quantam mechanics.

Erwin Schrödinger

Jan 23, 1926

Erwin Scrodinger published a paper in January on wave mechanics and what is now known as the Schrodinger equation. This paper, and the ones that succeeded it, are celebrated for creating a revolution in quantum mechanics and in physics and chemistry.

Werner Heisenberg

Apr 23, 1927

His most important contribution is the Heisenberg Uncertainty Priciple. We can know neither the velocity or location of an electron at any given time.

Werner Heisenberg

Apr 23, 1928

Published book , 'The Physical Principles of Quantum Theory' explaining his ideas.

Louis Debroglie

Apr 23, 1929

Discovered that electrons can act like both waves and particles.

James Chadwick

Feb 27, 1932

Used Curie's research to discover neutron. Discovered neatrons and protons ahve similar mass. Now concluded that nucleus contain neutrons and protons.

Aristotle

Mar 2, 2022

Theorized that all matter is made from the elements wind, fire, water, and earth.