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400
400 B.C. Democritus
Democritus was the first to note the existence of the atom. He proposed that the universe is composed of only atoms and the space they move in. He also believed that atoms are infinite, indivisible, and join together to form objects. -
Antoine Lavoisier
Antoine Lavoisier is best known for discovering oxygen's role in combustion. He also recognized and named oxygen and hydrogen in 1783. He also experimented with compounds and chemical reactions to develop the law of conservation of mass. -
John Dalton
John Dalton developed five rules of atoms, only three of which remain in the modern atomic theory. The law of conservation of mass supports his statement that atoms are not created or destroyed. The law of definite proportions supports his statement that each different chemical compound is composed of the same atoms. The law of multiple proportions supports his statement that the ratio of atoms always stays the same in compounds. -
J.J. Thomson
JJ Thomson is credited for discovering the electron, proving that the atom can be split into smaller parts. He made this discovery by experimenting with cathode-ray tubes and found that cathode rays are negatively charged. -
Marie Curie
Marie Curie is the only woman credited for her contribution to the atomic theory. Her studies in radioactivity led to her discovery of radium and polonium, which earned her a Nobel Prize. She also studied many other chemical compounds and showed that the radiation's strength didn't depend on the compound being studied. -
Max Planck
Max Planck is the originator of the quantum theory of energy, which states that energy or matter can be emitted or absorbed in small untits called quanta. His work helped better understand the atomic and subatomic processes. -
Robert Millikan
Robert Millikan is best known for his oil drop experiment, which helped him discovered the that there was a small charge. That small charge turned out to be the charge of an electron. -
Ernest Rutherford
Ernest Rutherford is well known for his gold foil experiment, in which he fired radioactive particles through a thin gold metal and used screens coated in zinc to detect where the particles deflected. Most of the particles went straight through like expected, but 1 in 8000 deflected off of the foil. Rutherford concluded that a very small force with a positive charge (the nucleus) deflected the particles. -
Niels Bohr
Studying under Rutherford, Niels Bohr furthered the gold foil experiment by stating that the "empty space" was actually occupied by electrons orbiting the nucleus like planets around the sun. This greatly improved the understanding of the atom's structure and the charges of the subatomic particles. -
Albert Einstein
Albert Einstein became famous for his theory of relativity, which stated that light energy can be absorbed or diffused only through detached packets (aka quanta). This theory earned him a Nobel Prize. Through his work, he proved that heat results from the motion of atoms and molecules. -
Louis de Broglie
Louis de Broglie introduced the concept of the "particle-wave," which explains the movement of particles and atoms. This helped scientists better understand how atoms, molecules, and protons move around. -
Werner Heisenburg
Werner Heisenburg developed new theories related to Max Planck's quantum mechanics about how electrons behave. -
Erwin Schrodinger
Schrodinger "finalized the puzzle" of electron movement by introducing the theory that they moved in waves, which showed that they couldn't be precisely calculated with mathematical equations. He also stated that the electron path cannot be traced, but instead shapes an electron cloud in which some areas are more dense than others. -
Werner Heisenburg
In addition to Heisenburg's contributions to the quantum theory, he has introduced the "uncertainty principle," which explains how it is impossible to know exactly where and how fast something is moving. This helped him prove that electrons revolve around the nucleus in a definite velocity. -
James Chadwick
James Chadwick officially discovered the neutron by testing a sample of beryllium bombarded with alpha particles emitting radiation. This experiment led to his discovery of a neutrally charged particle that didn't effect the magnetic field. This particle became known as the neutron, the third main subatomic particle.
