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600 BCE
Acharya Kanad the First
Acharya Kanad is believed to be the first person ever to formulate an atomic theory. It is said that Kanad dedicated his life trying to create the smallest particle of the matter he possibly could. His predictions were that these tiny particles were indestructible, attracted to other particles, as well as could come together to form compounds. -
490 BCE
Empedocles's Theory of Elements
Empedocles was a philosopher in ancient Greece during the dawn of scientific thought. Empedocles hypothesized that everything is made of four elements air, fire, wind, and earth. Opposing the one element theory of the philosophers before him. While his hypothesis was incorrect it was a step in the right direction. -
460 BCE
Democritus's Theory of the Atom
Democritus was a Greek scientist that theorized the atom. His hypothesis was that everything is made of small particles. His reasoning for this is that when an object is broken in two it does not chemically change. If you break an object down enough you are eventually left with an indestructible invisible particle. -
John Dalton's theory of the Atom
John Dalton rebirthed the theory that all matter is made of tiny particles called atoms. He added to Democritus's theory by stating that each element's atom is unique in size, mass, and weight. He believed that compounds were the combination of different atoms in specific ratios. He hypothesized that chemical reactions are just the rearrangement of the atoms of the reactants. His research and theory suddenly explained many chemical pheromones. Building the foundation for all atomic theory. -
J.J Thomson's Discovery of the Electron
J.J Thomson's largest contribution to atomic theory was through his discovery of the electron. His experiments using cathode-ray tubes proved the existence of his discovery while also proving atoms can be visible to the eye in the form of electricity. Given this new discoveries, the atomic model had to be revised. Thomson developed a diagram of the atom now known as the plum pudding model. It would remain relevant until 1911 when Earnest Rutherford discovered electron orbitals. -
Marie Sklodowska Curie
Marrie Sklodowska's main contribution to chemistry was through the development of her theory of radioactivity. Within her studies of radioactivity, she discovered two elements (polonium and radium), and developed methods in discovering elemental isotopes. Her achievements won her two Nobel Prizes, the 1903 Nobel Prize in physics and the 1911 Nobel Prize in Chemistry. This made her the first woman to win a Nobel Prize, and the first person to win two Nobel Prizes. -
Hanataro Nagaoka's Atomic Diagram
When J.J. Thompson released his plum pudding model in 1903 it was rejected by many. One of these people was Japanese physicist Hanataro Nagaoka, who questioned the plum pudding model's legitimacy based on repulsion laws. Nagaoka released his own model of the atom, which instead of having electrons scattered throughout had a ring of electrons connected to the nuclease with electronegative bands. -
Albert Einstein's Theory of Relativity
Albert Einstein's theory of relativity revolutionized quantum physics and was well before it's time. When Einstein released his theory of relativity in 1905 he proved the existence of electrons with an ordinary microscope. His theory showed that electron negativity is relative and is not at a fixed value proving electrons are always moving. -
Earnest Rutherford's
Earnest Rutherford is largely accredited for the discovery of the nucleus and creating the notion that electrons circle a positively charged nucleus. His gold foil experiment allowed him to study the trajectory of the electrons he shot at the gold foil. His finding contradicted J.J. Thompsons plum pudding model. Rutherford explained the atom consists of mainly empty space. -
Neils Bohr
Neils Bohr developed a new model alongside Earnest Rutherford. This new model was unique in showing different electron orbitals and a defined positively charged nucleus. Rutherford's previous model did not show multiple orbitals. He discovered electronegative radiation, and stated it occurred when an electron jumped from one orbital to another. -
Max Planck's Quantum Theory
Max Planck won the Nobel Prize for physics in 1918 for his discovery of quantum theory. Planck theories explained the intensity of light based on the electrons of the substance they came from. This shaped our thinking of atomic and subatomic processes. -
Satyendra Nath Bose
Satyendra Nath Bose produced a theory about condensates. He developed this theory with Alber Einstien. His theory centered around the two main subatomic particles. He specifically found out the "god" particle through this theory. This relates to atomic theory because everything is made of matter and knowing the subatomic particles and how they operate can help us better understand atomic theory. -
Louis DeBroglie
Louis De Broglie developed a theory on quantum physics which stated anything that is moving has wavelengths. Broglie's extensive research gave birth to wave mechanics. Albert Einstien was a significant follower of De Broglie and even applied his theories and ideas to his own. -
Werner Heisenberg's Uncertainty Principle
Werner Heisenberg's uncertainty principle allowed him to determine the approximate location and velocity of electrons in an atom. His theory proved that in quantum mechanics scientists are not able to measure multiple quantum variables at once. -
Wolfgang Pauli's Principle
Wolfgang Pauli's principle determined that no two electrons in the same atom can have the exact same quantum numbers. He also is credited for the discovery of the neutrino a particle with no mass that carries off energy. For his work, he was awarded the Nobel Prize for physics in 1945. -
Erwin Schrodinger
Erwin Shrodinger's greatest contribution to atomic theory must be his invention of the electron cloud model. Shrodinger was able to mathematically determine the most likely location of electrons within the atom. This is important because we were never able to get a reasonable prediction on the whereabouts of an electron before Schrodinger's discovery. -
James Chadwick
Chadwick discovered the Neutron thorough a series of tests. The test proved the presence of neutrons. In these tests he used scattered data to prove his theory. Up until 1932, protons and neutrons were discovered but neutrons were not. He won a Nobel Prize in 1932 for his work. -
Irene Joliot-Curie
Irene Joliot-Curie did important work on both artificial and natural radioactivity and earned a joint Nobel Prize in chemistry with her husband. In 1938, she released her research on the behavior of neutrons on heavy elements which sped the advancement of uranium fission greatly. -
Dorothy Crowfoot Hodgkin
Dorothy Crowfoot Hodgkin was able to determine the three-dimensional shapes of molecules using X-ray technology. She decided to use this technology for the most complex natural organisms that are vital for the survival of mankind. This process was very stressful and required multiple calculations to be completed. -
Ronald J. Gillespie
Ronald J. Gillespie studied the shapes of molecules and developed his very own theory, the Valence Shell Electron Pair Repulsion Theory. This helped scientists predict the shapes of molecules by determining the number of electrons in each orbital. Some other notable work of Gillespie is his studies into the development of superacids which opened an entirely new field of chemistry. -
Robert J. LeRoy
Robert J. LeRoy has two significant theories in the field of chemistry. The first is the development of the LeRoy-Bernstein theory. This theory focuses on vibrational energy levels of electrons. The second the derivation of the LeRoy radius, a mathematical way of determining the distance between different molecules nuclei. The ability to do this would help other scientists expand our ideas of intermolecular bonding. -
Richard F.W. Bader
Richard Bader developed a theory that contradicted the traditional Bohr Rutherford model. He stated that electrons actually don't follow orbitals. He discovered that the electron density determines the properties and behaviors atoms have.
