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400
Democritus
~400 B.C
Ancient Greek Philosopher Democritus was the first scientist to identify that matter could be made up of pieces called, "atomos" which means,"not to be cut" based off of his speculation that items would eventually reach a point at which they could not be split. He stated that these " atomos" would be invisible to the human eye and they would not change, rather they would move rapidly colliding with other "atomos". -
Period: 400 to
history of the atom
400 B.C to 1940 -
John Dalton
Scientist John Dalton is coined as the Father of Modern Atomic Theory. His theory consisted of five parts. One, all matter is composed of atoms, two, all atoms of the same element are identical, three, atoms cannot be made or destroyed, four, different elements have different types of atoms, five, chemical reactions occur when atoms are rearranged. From this he concluded that atoms of an element are identical in their mass. -
The Absorption of Gases by Water and other Liquids
This was the first published tab of atomic weights, written by John Dalton -
Henri Becquerel
French scientist Henri Becquerel is notably famous for his work where he observed that uranium atoms behave in commonality where they emit rays of radiation when placed near photographic plate causing them to react spontaneously. -
Joseph Thomson
British physicist Joseph Thomson is credited with the discovery of the electron from experiments set up to observe the habits of cathode rays in a vaccum tube. The deflection of these rays provided evidence that,"bodies much smaller than atoms" exist. Using his observations, Thomson made the Plum Pudding model of an atom which shows that electrons are positioned by electrostatic forces. -
Radioactivity
Scientist Marie Curie focused heavily on radioactivity, a term that she came up with, by running experiments to find ways to separate radioactive residues and radium, an element that she discovered, to study it and its behaviors. Curie also discovered her first of two elements and named it Polonium -
Nobel Prize of Physics
Given to Henri Becquerel for his discovery of spontateous decomposition -
Oil Drop Experiment
Scientist Robert Millikan performed what is known as the oil drop experiment. This experiment consisted of Millikan putting a charge into a small drop of oil. His goal was to prevent the oil drop from falling. By figuring out the gravity emitted by this drop of oil, he could conclude the electric charge that one drop would have. From this he found out that the specific charge was a multiple of -1.6x10 -19C, also known as the charge of one single electron. -
Gold foil experiment
This experiment was performed by scientist, Ernest Rutherford, using a thin sheet of gold foil and the firing of particles, surrounded by a a zinc sulfide sheet. The experiment shows that most of the particles passed through the gold sheet, but .0125 percent of the particles were deflected. This allowed Rutherford to make his theory and model of the atom that most of it was made up of empty space, while most of the weight is held at the small nucleus made up of protons and neutrons. -
Planetary Model of the atom
Scientist Niels Bohr came up with his own pictoral model of what an atom resembles. In the center he has the nucleus, made up of the subatomic particles, protons and neutrons, with electrons at different energy levels orbiting the nucleus as if the electrons are planets in a solar system. Bohr came up with the idea that electrons travel in specific energy levels based of off states of energy, the lowest being ground state, then first excited state, etc. -
Wave Particle Duality theory
Louis DeBroglie, a French scientist, published a theory on electron waves. His thesis stated that electron waves act as both wavelengths and particles. Stating that theory meant that electrons would revolve around the nucleus in a strict motion. The theory of DeBroglie is used to rationalize why subatomic particles have been able to appear in places that are not traditional. -
Uncertainty Principle
German scientist Werner Heisenberg came up with a theory about the positioning of electrons. He stated that it is uncertain to know where an electron is and at what veolcity it is traveling at the same time as the electron is around the nucleus. Along with this came the cloud model, which dictates that electrons do not travel in a neat orbit, rather electrons float in a "cloud" of elctrons around the nucleus. -
Electron Probability
Scientist Erwin Schrodinger came up with a mathematical equation that allowed people to determine the probability of electrons in an atom. The place where the electrons are to be found is called the orbital. This is a space around the nucleus which is known to hold the electron ninety percent of the time. He stated that an orbital doesnt neccessarily mean an orbit, but there could be different orbitals for different energy levels around the nucleus containing electrons. -
The neutron
Scientist James Chadwick is highly known for his discovery of the subatomic particle, the neutron. He found that the neutron held no electrical charge and was able to overcome electric barriers and was able to manage splitting even some of the worlds heaviest elements. Chadwick was able to use this in his nuclear studies and establish stepping stones in the making of the atomic bomb. Chadwicks nuclear model was showed the neutron to have a neutral charge with a strong nuclear force to protons
