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500 BCE
Plato's Atomic theory
Plato theorized that atoms broke down mathematically into triangles and that the triangles could join together and form different shapes. He also associated certain elements with certain shapes. For example, he associated fire with a tetrahedron, water with an icosahedron, air with an octahedron, and Earth with a cube. The exact year Plato formed his version of the atomic theory is not known, but it was around 5th century B.C. -
430 BCE
Democritus's Atomic theory
Democritus's atomic theory states that atoms are in continuous motion, atoms are physically indivisible, there is an empty space between atoms, atoms are indestructible, and there is an infinite number of atoms and kinds of atoms that vary in shape and size. -
760
The Alchemists's Atomic Theory
The Alchemists proposed that all metals were formed from two principles, sulfur and mercury in different proportions. They believed that if you slightly change the proportions of one of the two principles could transform one metal into another. -
Robert Boyle's Atomic Theory
Robert Boyle believed all substances were made up of corpuscles, which are now called atoms. He also discovered the inverse relationship between pressure and volume in a gas. He defined the current idea of an element and introduced many more standard chemical tests. He was also the first to suggest that the world was made of many "unmingled bodies", this refers to the elements, which together form mixed bodies resulting in complete compounds. -
Antone Lavoisier's Atomic Theory
Antone Lavoisier defined that matter was composed of atoms that were not created or destroyed during chemical reactions. He also grouped elements into gasses, metals, non-metals, and earthly simple substances. He organized these elements based on their physical and chemical properties. -
John Dalton's Atomic Theory
John Dalton's atomic theory is made of four steps. Number one, all matter is made up of atoms. Number two, all atoms of a given element are identical in mass and properties. Number three, compounds are combinations of two or more different types of atoms. And finally, number four, a chemical reaction is a rearrangement of atoms. John Dalton also created the Billiard Ball Model. -
Amedeo Avogadro's Atomic Theory
Amedeo Avogadro proposed equal volumes of gasses contain equal numbers of molecules and that elemental gasses are composed of two atoms. He also distinguished between atoms and molecules as different levels of complexity of matter. His work was ignored for fifty years. -
Pierre and Marie Curie's Atomic Theory
Pierre and Marie Curie hypothesized that radioactive particles cause atoms to break down and release radiation. They discovered polonium and radium which were two new radioactive elements. They confirmed that radioactivity depends on atoms themselves and now the individual arrangements. They created the field of atomic physics and found a way to get the atomic mass of an atom. Marie Curie won the Nobel Peace Prize for Physics in 1903 for her discoveries. -
Dmitri Mendeleev's Atomic Theory
Dmitri Mendeleev arranged the elements in order of increasing the relative atomic mass. He delivered a full paper to the Russian Chemical Society showing the characteristics of the elements and how they "recur at a periodic interval as a function of their atomic weight". He suggested that the physical and chemical properties of elements and compounds showed a periodic trend. -
JJ Thompson's Atomic Theory
JJ Thompson discovered the first subatomic particle, the electron. He proposed a model of the atom in which negative electrons are scattered throughout a sphere of positive charge called the Plum Pudding Model. -
Albert Einstein's Atomic Theory
Albert Einstein mathematically proved the existence of atoms. He suggested that any liquid is made up of molecules and that molecules are always in random, ceaseless motion. -
Ernest Rutherford's Atomic Theory
Ernest Rutherford discovered that the atom is mostly empty space surrounding a massive nucleus. He proposed the Rutherford model that described the atom as having a tiny, dense, positively charged nucleus. Ernest Rutherford also created the solar system model. -
Robert Millikan's Atomic Theory
Robert Millikan is most known for his oil drop experiment. His oil drop experiment allowed him to measure the charge on a single electron. It proved that electrons have a fixed charge. It showed the charge of an electron was always and integral multiple of a small, but finite value. It also allowed scientists to calculate the mass of a single electron. Robert Millikan won the Nobel Peace prize for physics in 1923 for his contributions to the current atomic model. -
Neils Bohr's Atomic Theory
The Bohr hydrogen model suggest that electrons orbit the nucleus at fixed energy levels. He created an atomic model that described an atom as a small, electron surrounded positively charged nucleus where the electrons travel in circular orbits around the nucleus like planets around the sun in the solar system. -
Henry G.J. Mosely's Atomic Theory
Jenry G.J. Mosely determined the charges on the nucleus of most atoms and found that the atomic number is equal to the number of protons. He recognized the periodic table based on atomic number rather than atomic mass. He also showed major properties of an element are determined by atomic number. -
Werner Heisenberg's Atomic Theory
Werner Heisenberg discovered a way to formulate quantum mechanics in terms of matrices. He created the Heisenberg Uncertainty Principle which states it is impossible to precisely measure position and momentum of a particle at the same time. He won the Nobel Peace Prize for Physics in 1932 for his discoveries. -
Erwin Schrodinger's Atomic Theory
Erwin Schrodinger developed a quantum mechanical model of the atom. He used mathematical equations to describe the likelihood of finding an electron in a certain position. His wave equation could be used to sold and give accurate descriptions of the energy of an electron in an atom due to vibrational modes and the creation of peaks and troughs when these electrons are treated as waves. -
James Chadwich's Atomic Theory
James Chadwich discovered the neutron. His discovery forced revision of the cloud model. This discovery made the development of the atomic bomb possible. He participated in the top-secret Manhattan Project that led to the deployment of atomic bombs on Hiroshima and Nagasaki, leading to the surrender of Japan in World War ll. James Chadwich received the Nobel Peace Prize for Physics in 1935 for his discoveries.