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465 BCE
Democritus
Democritus theorized that atoms cannot be destroyed, differ in size, shape and temperature, are always moving, and are invisible, HE also believed that there are an infinite number of atoms. -
465
Democritus
Democritus theorized that atoms cannot be destroyed, differ in size, shape and temperature, are always moving, and are invisible. He believed that there are an infinite number of atoms. -
Antoine Lavoisier
Lavoisier proposed the Combustion Theory which was based on sound mass measurments and named the element oxygen. He also proposed the Law of Conservation of Mass which represents the beginning of modern chemistry. -
Joseph Louis Proust
Joseph Louis Proust first published his Law of Definite Proportions. This law states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created. -
John Dalton
Dalton introduced the idea that atoms of different elements could be universally distinguished based on their varying atomic weights. He became the first scientist to explain the behavior of atoms in terms of the measurement of weight. He also concluded that atoms couldn't be created or destroyed. -
Michael Faraday
Faraday liquefied various gases, including chlorine and carbon dioxide. His investigation of heating and illuminating oils led to his discovery of benzene and other hydrocarbons. -
Henri Becquerel
Becquerel discovered radioactivity which was an early contribution to the atomic theory. He discovered radioactivity while experimenting with uranium and a photographic plate. -
JJ Thomson
Thomson developed the concept of the mole and proposed a system of symbols to represent atoms of different elements. -
Marie & Pierre Curie
Marie & Pierre Curie discovered the elements radium and polonium while studying radioactivity. -
Albert Einstein
Einstein formulated the Special Theory of Relativity -
Robert Millikan
Millikan determined the unit charge of the electron with his oil drop experiment at the University of Chicago. This allowed for the calculation of the mass of the electron and the positively charged atoms. -
Ernest Rutherford
Rutherford overturned Thomson's model with his well-known gold foil experiment in which he demonstrated that the atom has a tiny, heavy nucleus. -
Neils Bohr
Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus. -
Max Planck
Planck was a German physicist and is best known as the originator of the quantum theory of energy for which he was awarded the Nobel Prize. His work contributed significantly to the understanding of atomic and subatomic processes. -
Erwin Schrodinger
Erwin Schrodinger was an Austrian physicist who took the Bohr atom model a step further. He used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model. -
James Chadwick
Chadwick discovered the neutron. With the discovery of the neutron, an adequate model of the atom became available to chemists.