Information from timeline taken from http://www.barcodesinc.com/articles/timeline-on-atomic-structure.htm
Democritus’ atomic theory posited that all matter is made up small indestructible units he called atoms.
Isaac Newton theorized a mechanical universe with small, solid masses in motion.
John Dalton proposed that elements consisted of atoms that were identical and had the same mass and that compounds were atoms from different elements combined together.
Michael Faraday developed the two laws of electrochemistry:
1. The mass of substance produced is proportional to the quantity of electricity.
2. A given quantity of electricity produces fewer moles of substances with higher oxidation numbers.
CliffsNotes.com. Faraday's Laws.
Julius Plücker built one of the first cathode-ray tubes.
Dmitri Mendeleev created the periodic table.
James Clerk Maxwell proposed the theory of electromagnetism and made the connection between light and electromagnetic waves.
G.J. Stoney theorized that electricity was comprised of negative particles he called electrons.
Sir William Crookes’ experiments with cathode-ray tubes led him to confirm the work of earlier scientists by definitively demonstrating that cathode-rays have a negative charge.
Eugene Goldstein discovered canal rays, which have a positive charge equal to an electron, later called Proton.
Wilhelm Roentgen discovered x-rays.
Henri Becquerel discovered radiation by studying the effects of x-rays on photographic film.
J.J. Thomson determined the charge to mass ratio of electrons.
Marie Sklodowska Curie discovered radium and polonium and coined the term radioactivity after studying the decay process of uranium and thorium.
Ernest Rutherford discovered alpha, beta, and gamma rays in radiation.
Max Planck proposed the idea of quantization to explain how a hot, glowing object emitted light.
Richard Abegg found that inert gases have a “stable electron configuration.”
Hantaro Nagaoka proposed an atomic model called the Saturnian Model to describe the structure of an atom.
Hans Geiger invented a device that could detect alpha particles.
Frederick Soddy came up with the term "isotope" to explain the unintentional breakdown of radioactive elements.
H.G.J. Moseley discovered that the number of protons in an element determines its atomic number.
Francis William Aston invents the mass spectrograph, capable of separating isotopes by measuring the minute differences in their masses. He successfully identified 212 existing isotopes.
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.
Freudenrich, Ph.D., Craig. "How Atoms Work" 01 February 2001. HowStuffWorks.com. http://science.howstuffworks.com/atom.htm
Paul Adrien Maurice Dirac begins the modern theory of Antimatter with a paper called "The Quantum Theory of the Electron".
Cockcroft / Walton created the first nuclear reaction, producing alpha particles
James Chadwick discovered neutrons, particles whose mass was close to that of a proton.
Lise Meitner, Otto Hahn, and Fritz Strassman discovered nuclear fission.
Glenn Seaborg discovered eight transuranium elements.