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442 BCE
Democritus
Democritus was a Greek philosopher who believed that all things were made of tiny particles called “atomos”. He continued Leucippus his teachers theory on after he died and finished it and its now known that everything is composed of atoms which are physically but not geometrically indivisible -
Period: 350 BCE to
chemistry project By: Morgan Turcotte A1
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384
Aristotle
Aristotle believed that everything was not composed of atoms but of the elements; Fire, water, Earth, and air. He believed that everything was made of small amounts of these elements. This enhances Democritus’ theory in a deeper aspect by explaining what the tiny particles in his theory are. -
Antoine Lavoisier
Antoine Lavoisier, The “father of modern chemistry”, he was a French nobleman in the histories of chemistry and biology. He stated the first version of the law of conservation of mass, he recognized and named the elements oxygen and hydrogen. He constructed the metric system and wrote the first extensive list of elements and discovered that although matter may change its form or shape, its mass always remains the same. -
John Dalton
John Dalton was a British chemist and physicist that thought matter was composed of atoms of different weights combined in ratios by weight, he proposed that these atoms were spherical and always in motion. Dalton printed his first published table of relative atomic weights. Six elements appeared; hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus, he believed that all atoms of a given element are identical, elements are made of particles named atoms that cannot be destroyed or created. -
Henri Becquerel
Henri Becquerel discovered the radioactivity of atoms. He was inspired by the recent discovery of X-rays, he hypothesized that phosphorescent elements like uranium would emit a penetrating radiation similar to the X-rays. He later shared the Nobel prize with two of his students Marie and Pierre Curie -
J.J Thomson
J.J Thomson discovered the electron, using a series of electric discharge in a high vacuum cathode-ray tube. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of “bodies much smaller than atoms”. He calculated this as having a very large value for the charge-to-mass ratio. -
Marie and Pierrie Curie
The two are best known for their pioneering work in the study of radioactivity, which led to their first discovery in 1898 of the elements Radium and Polonium. They studied under Becquerel and won a Nobel Prize for their work and later Marie won another becoming the first person, let alone woman to win the prize twice. -
Max Planck
Max Planck was a German Theoretical physicist considered to be the founder of quantum theory, and one of the most important physicist of the 20th century. He realized that light and other electromagnetic waves were emitted in discrete packets of energy that he called “quanta”. -
Robert Millikan
Robert Millikan was an American experimental physicist, and Nobel Laureate in physics for his measurement of the charge on the electron and for his work on the photoelectric effect. His experiment measured the force on tiny charged drops of oil suspended against gravity between two metal conductors. -
Earnest Rutherford
Earnest Rutherford was British-New Zealand chemist and physicist who became known as the father of nuclear physics. In his early work he discovered the concept of radioactive half-life. In 1911 he postulated that atoms have their positive charge concentrated in a very small nucleus and the Rutherford model, or planetary, model of the atom was born though this discovery of Rutherford scattering in his gold foil experiment. -
Henry Mosely
Henry Mosely worked with Rutherford in a group on radioactive chemical elements. He attempted to use high positive voltages to pull beta particles back into their radioactive source (he tried to prove Einstein’s theory that mass increases with velocity). Mosely surprisingly generated high voltages on a radioactive source creating the world’s first radioactive battery. He called it the radium battery. -
Niels Bohr
Niels Bohr created a model in which he thought was the structure of an atom. He believed the electrons orbited the nucleus and chemical properties being determined by how many elecetrons are in the outer orbit, this was called the Bohr model. Later they corrected this theory of electrons orbiting by proving electrons actually are in an electron cloud and chemical properties being determined by how many elecetrons are in the outer orbit -
Werner Heisenberg
Werner Heisenberg formulated a type of quantum mechanics based on matrices. In 1927 he proposed the “uncertainty relation”, setting limits for how precisely the position and velocity of a particle can be simultaneously determined. Heisenberg got to his discovery off of Bohr’s work needing to be developed to suit more complicated atoms and molecules. -
Erwin Schrodinger
Erwin Schrodinger, an Austrian physicist took the bohr model further by using mathematical equations to describe the likelihood of finding an electron in a set position. The atomic model was known as the quantum mechanical model of the atom. Unlike the Bohr model the quantum mechanical model does not define the exact path of an electron but rather predicts the location. -
James Chadwick
James Chadwick bombarded beryllium atoms with alpha particles. An unknown radiation was produced. Chadwick interpreted this radiation as being composed of particles with a neutral electric charge and the approximate mass of a proton. This particle became known as the neuron. With the discovery of the neuron chemist could have an accurate model of the atom.
