June 15, 2020
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Atomic Theory - Jessica Ashton
⟶ Updated 27 Sep 2017 ⟶
List of edits
Start of Atomic Theory Timeline
Democritus' atomic theory stated that all matter is made up of small indestructible units he called atoms
Aristotle does not believe in atomic theory, rather he believes everything is made up of the four elements
Isaac Newton theorized a world with solid masses in motion
Antoine Lavosier created the Law of Conservation of Mass
Joseph Priestly discovered Oxygen
Joseph Proust creates the law of Definite Proportions
Joseph Prous proposed the Law of Constant Composition
Dalton Proposed that elements consisted of atoms that were identical and had the same mass
Joseph Gay-Lussac announced the Law of Combining Volumes
Dalton went on to say that matter is made up of atoms and cannot be divided into smaller pieces and they cannot be destroyed
Michael Faraday developed the two laws of electrochemistry
Wilhelm Roentgen observed chemicals that glow meaning that some rays were not deflected
Hantaro Nagaoka claimed that an atom has a nucleus
Dmitri Ivanovich Mendeleev creates the first periodic table
The Crookes demonstrate that cathode rays travel in straight lines
James Clerk Maxwell proposed the theory of electromagnetism
G.J. Stoney theorized that electricity was comprised of negative particles known as electrons
Sir WIlliam Crookes discovers that cathode rays can be deflected by electric fields meaning they have a negative charge (electrons)
E. Goldstein discovers canal rays which have a positive charge equal to an electron
Wilhelm Roentgen discovered X-rays
Henri Becquerel discovered radiation by studying effects that X-rays have on photographic film
J.J. Thomson determined the charge to mass ratio of electrons
The Curies discovered radium and polonium when they started to investigate radioactive substances
Rutherford discovered alpha, beta, and gamma rays in radiation
Marie Sklodowska Curie coined the term radioactivity after studying the decay process of uranium and thorium
Frederick Soddy came up with the term "isotope" to explain the unintentional breakdown of radioactive elements
Max Planck experimented with black body(an object that absorbs electromagnetic radium) which led to his Planck Postulate which describes the stability of electrons
Hantaro Nagoaka proposed an atomic model called the Saturnian Model to describe the structure of an atom
Richard Abegg found that inert gases have a stable electron configuration
J.J. Thomson created the "plum pudding" model of an atom
Albert Einstein was capable of proving the existence of atoms and was capable of counting them
Hans Geiger invented a device that could detect alpha particles
Robert Milikan proves that electrons have the same charge and mass
J.J. Thomson discovered isotopes of stable elements
Frederick Soddy proposes the concept of isotopes, that elements with the same chemical properties may have different atomic weight
Gilbert N. Lewis publishes "The Atom and the Molecule" which is the foundation of Valance Bond Theory
H.G.J. Moseley discovered that the number of protons in an element determines its atomic number
Francis William Aston used a mass spectrograph to identify 212 isotopes
Otto Stern and Walther Gerlach establish concept of quantum mechanical spin in subatomic particles
Niels Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.
Louis de Broglie proposed that electrons have a wave/particle duality
Wolfgang Pauli develops the exclusion principle, which states that no two electrons around a single nucleus may have the same quantum state, as described by four quantum numbers.
Erwin Schrodinger combined the equations for the behavior of waves with the de Broglie equation to generate a mathematical model for the distribution of electrons in an atom.
Cockcroft / Walton created the first nuclear reaction, producing alpha particles
Paul Dirac proposed the existence of antiparticles.
James Chadwick discovered neutrons, particles whose mass was close to that of a proton.
Lise Meitner, Hahn, Strassman discovered nuclear fission.
Murrey Gal-Mann proposed the ideas of quarks(a part of an atom)
Glenn Seaborg discovered eight transuranium elements.
End of Events
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