-
Period: 200 to
History of the Atom
-
400
Aristotle
Aristotle was also a Greek philosopher. He proposed that the idea of the atom was worthless. He argued against the existence of atoms. He thought that different substances were made up of different combinations of fire, air, earth, and water. Even though we now know he was wrong, many people believed him because everyone knew that he was a very smart man. -
460
Democritus
Democritus was a Greek philosopher. He was the first one to develop the idea that all matter was made up of atoms; there was no previous theory, He got the word tom from the Greek word "atomos", meaning indivisible. Democritus proposed that an atom is too small to see, they are unchangeable, indestructable, and they are indivisible. He said that they were completely solid and had no internal structure. He also thought thje atoms moved about in space to form different objects -
Antoine Lavoisier
Lavoisier was the first to discover that water is made up of hydrogen and oxygen. He also showed that chemical elements could not be created nor destroyed, just combined into different compounds in chemical reactions. This was later followed by the law of conservation of mass. He is considered the founder of modern chemistry -
John Dalton
John Dalton was an English chemist and meteorologist. He was not only the first one to make a list of atomic weights (of 21 elements), but he also proposed the standard symbols for each element. Dalton proposed that chemical elements were composed of atoms. He also discovered 3 big things about atoms and elements. 1. atoms of the same element all had the same mass. 2. different element atoms have different masses. 3. atoms could only be combined in small, whole number ratios to form compounds. -
Henri Becquerel
Becquerel is known for his discovery of radioactivity. Marie and Pierre Curie began their work on radioactive elements with Becquerel and in 1903 Becquerel received one Nobel Prize, and Marie and Pierre Curie shared another. -
JJ Thomson
Thomson was a physicist at Cambridge University, and is responsible for the discovery of the electron. He discovered this using a cathode ray tube, He proposed the idea of the atom not being indivisible, and the plum-pudding model. This is where the atom is a dense sphere made up of positively charged parts, along with studded negatively charge electrons (like raisins). -
Marie & Pierre Curie
They are best known for their work with radioactivity. this led to their discovery in 1898 of the elements radium and polonium. Their study of radioactive elements contributed to the understanding of atoms on which modern nuclear physics is based. They shared the 1903 Nobel Prize in physics with Becquerel for the discovery of radioactive elements. -
Max Planck
A German physicist who used the idea of quanta (discrete units of energy) to explain hot glowing matter; He was the originator of the quantum theory. He did many observations of radiation of heated materials. This led him to believe that energy did not flow in a steady continuum, but was emitted or absorbed in discrete units (quanta). -
Robert Millikan
Millikan was a professor at the University of Chicago. He found a way to determine the unit charge carried by an electron in 1909 with his oil drop experiment. He also proved that this quantity was a constant for all electrons, demonstrating the atomic structure of electricity. -
Ernest Rutherford
Rutherford, a former student of Thhomson, proposed that an atom consists of a small dense nuclues along with orbiting electron around it. The rest of the atom was mostly empty space. Rutherford found that it was mostly empty space by firing radioactive particles through metal foils. he found that 1 in every 8000 times, they were deflected, He is considered the father of nuclear physics. -
Neils Bohr
Neils Bohr was a student of J.J tompson and a colleage of Ernest Rutherford. His model is simply an improved model of Rutherfords and is based on quantum mechanics. Electrons orbit the nucleus in orbits that have a set size and energy. The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit. Radiation is absorbed or emitted when an electron moves from one orbit to another. Also, when an electron jumps from outer orbit to inner one, it emits light. -
Henry Moseley
Moselel was a British chemist who studied under Rutherford. He developed the application of X-ray spectra to study atomic structure. This led to more accurate positioning of elements on the periodic table by being able to determine atomic numbers more closely -
Erwin Schrodinger
Schrodinger published four papers that laid the foundation of the wave-mechanics approach to quantum theory. This came about because he wasnt satisfied with Bohr's orbital theory, he had the belief that atomic spectra should really be determined by some kind of eigenvalue problem. -
Werner Heisenberg
Heisenberg was once Neil Bohrs assistant. He is best known as a founder of quantum mechanics, the new physics of the atomic world, and especially for the uncertainty principle in quantum theory. The uncertainty principle says that the more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa. -
James Chadwick
In 1932, James Chadwick, who worked under Rutherford on radioactivity, proved that the atomic nucleus contained a neutral particle which had been proposed more than a decade earlier by Ernest Rutherford. He did this by first realizing the atomic # was always lower than the atomic mass of an alement. Since electrons had no mass, something besides protons had to make up the mass. He found there was in experiments tracking particle radiation.
