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400 BCE
Democritus
Proposed that "everything is composed of “atoms”, which are physically, but not geometrically, indivisible," suggesting that all matter is composed of tiny indivisible particles. Democritus is considered to be the "father of modern science" due to his atomic theory of the universe.
(~“Democritus (460—370 B.C.E.).” Internet Encyclopedia of Philosophy, www.iep.utm.edu/democrit/.) -
335 BCE
Aristotle
"Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter."
(~“Aristotle.” The-History-of-the-Atom, the-history-of-the-atom.wikispaces.com/Aristotle?responseToken=0a7cc3fe7bf25c74afdc61b4b4e176822.) -
Antoine Lavoisier
Lavoisier is known as the father of modern chemistry for his discovery of the role oxygen plays in combustion. "He established the law of conservation of mass, determined that combustion and respiration are caused by chemical reactions with what he named “oxygen,” and helped systematize chemical nomenclature, among many other accomplishments."
(~https://www.chemheritage.org/historical-profile/antoine-laurent-lavoisier) -
John Dalton
John Dalton proposed that all matter was composed of atoms. "While all atoms of an element were identical, different elements had atoms of differing size and mass."
(~Dalton's Atomic Theory. www.iun.edu/~cpanhd/C101webnotes/composition/dalton.html." -
Michael Faraday
"It was clear to Faraday that electrical forces were responsible for the joining of atoms in compounds. "
(~“Development of the Atomic Theory.” Abcte.org, www.abcte.org/files/previews/chemistry/s1_p3.html.) -
Henri Becquerel
Henri Becquerel discovered radioactivity.
(~“Development of the Atomic Theory.” Abcte.org, www.abcte.org/files/previews/chemistry/s1_p4.html.) -
J.J. Thomson
J.J. Thomson discovered electrons and demonstrated that cathode rays are negatively charged. He proposed that atoms were made of positive cares and negativley charged particles within them.
(~“Modern Atomic Theory: Models.” Abcte.org, www.abcte.org/files/previews/chemistry/s1_p5.html.) -
Albert Einstein
"Einstein treated matter and energy as exchangeable. Albert Einstein became famous for the theory of relativity, which laid the basis for the release of atomic energy."
(~“Albert Einstein.” Teslasociety.com, www.teslasociety.com/einstein.htm.) -
Robert Millikan
Robert Millikan measured the charge of an electron with his oil drop experiment. "Millikan was able to show that the charge on a drop was always an integral multiple of a small, but finite value."
(~“The Charge of an Electron (Robert Millikan).” Robert Millikan, chemed.chem.purdue.edu/genchem/history/millikan.html.) -
Ernest Rutherford
Rutherford described the atom as a small, dense, positively charged core called a nucleus, "in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun."
(~The Editors of Encyclopædia Britannica. “Rutherford Atomic Model.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 10 Aug. 2017, www.britannica.com/science/Rutherford-atomic-model.) -
Niels Bohr
Bohr proposed that electron move around the nucleus in a set orbit in energy levels. He proposed the theory for the hydrogen based atom based on quatum theory.
(~“Niels Bohr - Facts.” Nobelprize.org, www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-facts.html.) -
Max Planck
"Planck made many contributions to theoretical physics, but his fame rests primarily on his role as originator of the quantum theory. This theory revolutionized our understanding of atomic and subatomic processes, just as Albert Einstein’s theory of relativity revolutionized our understanding of space and time"
(~Stuewer, Roger H. “Max Planck.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 21 Apr. 2017, www.britannica.com/biography/Max-Planck.) -
Erwin Schroedinger
"Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position." This is known as the quantum mechanical model of the atom, or the electron cloud model.
(~“Development of the Atomic Theory.” Abcte.org, www.abcte.org/files/previews/chemistry/s1_p6.html.) -
Louis de Broglie
Louis de Broglie was a French Physicist who did research on quantum theory and proposed the wave nature of electrons.
(~Cline, Barbara Lovett. “Louis De Broglie.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 29 Jan. 2017, www.britannica.com/biography/Louis-de-Broglie.) -
James Chadwick
James Chadwick discovered the neutron, and "an adequate model of the atom became available to chemists."
(~“Development of the Atomic Theory.” Abcte.org, www.abcte.org/files/previews/chemistry/s1_p6.html.) -
Glenn T. Seaborg
"American nuclear chemist best known for his work on isolating and identifying transuranium elements."
(~Kauffman, George B. “Glenn T. Seaborg.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 23 May 2017, www.britannica.com/biography/Glenn-T-Seaborg.)
