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150
Aristotle
Aristotle thought that no matter how many times you cut a form of matter in half, you would always have a smaller piece of that matter. He also believed in the four elements of fire, water, earth, and air making up everything. -
150
Democritus
Democritus originally wondered if matter could be cut into smaller and smaller pieces forever and eventually theorized that it couldn't. He decided once a piece of matter had gotten so small, it couldn't be cut any more. He called this piece "atomos" which means "not to be cut." According to Democritus, atoms of the same matter would be made up of the same material but have varying shapes and sizes. He also believed that atoms were infinite and are always moving and capable of joying together. -
Antoine Lavoisier
Antoine Lavoisier is widely known as the father of modern chemistry. Lavoisier established the Law of Conservation of Mass. Lavoisier is also credited to making up the names of many of the different elements. He foundout that water was made up of hydrogen and oxygen. He actually even decided on the name oxygen for that particular element. He decided on that particular name because the word oxygen means "acid-former," and this expressed his theory that oxygen was an acidifying principle. -
John Dalton
John Dalton believed almost the same things that Democritus believed but with a few differences. Like the fact that Dalton believed that all the atoms of a given element were identical in their mass and properties. Dalton also introduced a couple of his own theories about the atom, like the fact that atoms can be neither created nor destroyed. A good way to describe how Dalton believed the atom looked like would be a billiard ball. -
Henri Becquerel
Henri Becquerel discovered radioactivity. Henri would expose some Uranium to the sun and then inspect the uranium to find crystals. One day he left it in a desk and when he took them out and inspected them, he found that the uranium had still grown crystals even though it hadn't been in the sun. This is where he found out that Uranium didn't need the sun to be radioactive. -
J.J. Thomson
Thomson changed the way that we had viewed the atom by discovering the electron. He theorized that the atom was divisible. He thought that the atom consisted of a sphere of positive charge with negatively charged electrons embedded in it. He also said that the positve and negative charges in an atom were equal, which meant an atom was nuetral. His atomic model is normally called "The Plum Pudding Model." The bread the positive part and the chunks in it the negative chunks. -
Marie & Pierre Curie
Marie Curie focused on radioactive properties of elements, especially radium. She took her inspiration from the scientist Henri Becquerel, who had dicovered radioactivity.Marie Curie developed methods for the separation of radium from radioactive residues to study the characterization and the careful study of its properties. -
Max Planck
Max Planck had the problem of radiation processes engaged in his attention and he showed that these were to be considered as electromagnetic in nature. From there, he was led to the problem of distribution of energy in the spectrum of radiation. Planck eventually figured out the relationship between the ener gy and the frequency of radiation. This marked a turning point in physics. -
Robert Millikan
Robert Millikan earliest major success was were he found an accurate determination of the charge carried by an electron. He also proved that this quantity was constant for all electrons. Later, he made the first direct photoelectric determination of Planck's constant. -
Ernest Rutherford
Ernest Rutherford found that an atom must have its mass concentrated on its center. He figured this out by shooting alpha particles through a microscopically thin sheet of gold, finding that some particles bounced back.The only way this could of happened, would have been if there was something bigger than electrons in the atom. Rutherford figures, in a atom, the nucleus is the center and circling around the nucleus are electrons. The nucleus would be like the sun and the electrons like planets. -
Henry Mosely
Henry Mosely is known for the establishment of the truly scientific basis of the Periodic Table of Elements by sorting chemical elements in the order of their atomic numbers. He found this by finding a systematic relation between wavelength and the atomic number. -
Niels Bohr
Niels Bohr refined Ernest Rutherford's model fo the atom by saying that electrons orbit the nucleus without losing energy, that electrons could move only in fixed orbits of specific energies, and that electrons with low energy would orbit closer to the nucleus while electrons with high energy orbit further from the nucleus. -
Werner Heisenberg
One of Heisenbergs most memorable discoveries is the Uncertainty Principle. This means that electrons do not travel in neat orbits. He calculated the behavior of electrons and brought more understanding into the pattern of an atoms electrons. -
Erwin Schrodinger
Erwin Schrodinger made an equation called Schrödinger's wave equation which came as a result of his dissatisfaction with the quantum condition in Bohr's orbit theory. This equation showed the quantum mechanical behavior of an atom. -
James Chadwick
James Chadwick iidentified the nuetron, the particle proposed by Rutherford as having significant mass and no charge. With the discovery of the neutron three subatomic particles were identified that would help explain observations made at the atomic level. Chadwick was able to explain the existence of isotopes through his discovery of the neutron. Isotopes of the same element have the same number of protons and electrons but differ in the number of neutrons found in their nucleus.
