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Period: 300 to
History of the Atom
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340
Aristotle
Aristotle didnt think atoms could be constantly moving if they were in a void. He beleived there were four elements and four qualities, and that they would align into their rightful place and be at rest. -
440
Democritus
Beleived that if you continually cut a substance in half, eventually you would get an "uncuttable" piece. He called these uncuttable pieces particles, which means indivisible in greek.He thought atoms were hard and small particles compiled by one substance and in one particular shape. He thought they were always moving and that they combined with each other. -
Antoine Lavoister
Antoine created the idea of having on single -common language for all of science to use. for example when someone called a substance iron, than everyone was to call it iron. This allowed for science to advance and for chemists to learn new properties of other metals and know how to organize them. -
John Dalton
He claimed the reason elements combined was because all elements are made up of atoms. He also published a three- part atomic theory.
1 All particles are made of atoms, they cant be divided or destroyed.
2.Atoms of the same elements are identical diferent element's atoms are different.
3. atoms join with other substances to create new and different substances. -
Pierre and Marie Curie
They began investigating the phenomenon of radioactivity recently discovered in uranium ore. Marie noted the residual material to be more "active" than the uranium itself. She concluded that the ore contained, in addition to uranium, new elements that were also radioactive. This led to the discoveries of the elements polonium and radium. -
Henri Becquerel
While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off rays. -
J.J. Thomson
Thomson used a cathode ray tube to inferr that there are small particles inside of every atom. This inference proved dalton's theory to be wrong. Particles can be divided. Through this expirament thomson also inferred that atoms must be negatively charged.Thomson purposed the plum pudding model which allowed scientefic advances to occur. -
Max Planck
Planck was able to deduce the relationship between the energy and the frequency of radiation. this was based on the revolutionary idea that the energy emitted by a resonator could only take on discrete values or quanta. The energy for a resonator of frequency v is hv where h is a universal constant, now called Planck's constant. -
Ernest Rutherford
In is experament rutherford shot a positively charged beam of particles through a sheet of gold foil. He thought if the particles were soft as jj thomson's plum pudding model had suggested than they would pass Through and continue in a straight line, Which most did. However some did not this showed that the plum pudding model was somewhat false, so rutherford created a new model. -
Robert Millikan
Determined the unit charge of the electron in 1909 with his oil drop experiment at the University of Chicago. Thus allowing for the calculation of the mass of the electron and the positively charged atoms. -
Henry Mosley
Mosley sorted the elements of the periodic table to be more organized. He also discovered that the energy of x-rays emitted by the elements increased in a linear fashion with each successive element in the periodic table. In 1913, he proposed that the relationship was a function of the positive charge on the nucleus. This rearranged the periodic table by using the atomic number instead of atomic mass to represent the progression of the elements. This new table left additional holes for elemen -
Neils Bohr
In 1913, Bohr published a theory about the structure of the atom based on an earlier theory of Rutherford's. Rutherford had shown that the atom consisted of a positively charged nucleus, with negatively charged electrons in orbit around it. Bohr expanded upon this theory by proposing that electrons travel only in certain successively larger orbits. He suggested that the outer orbits could hold more electrons than the inner ones, and that these would determine the atoms chemical properties. -
Erwin Schrodinger
Schrodinger developed the wave mechanics. It became the second formulation of quantum mechanics. After reading de Broglie’s work Schrodinger began to think about explaining the movement of an electron in an atom as a wave and eventually came out with a solution. He tried to visualize electron as `wave packets’ made up of many small waves so that these wave packets would behave in the same way as a particle in classical mechanics. However, these packets were later shown to be unstable. -
James Chadwick
discovered the neutron in 1932. Chadwick was a collaborator of Rutherford's. The discovery of the neutron led directly to the discovery of fission and ultimately to the atomic bomb.
