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330
B.C. Aristotle
Instead of atoms, Aristotle beleived that all matter was made up of four elements: fire, water, air, and earth. -
460
B.C. Democritus
He theorized that matter was made up of tiny, indivisible particles. To test this, he broke a seashell into tiny peices until it could be broken no more. He called these particles "atoms" because they were indivisible. -
Lavoisier
He came up with the Law of Conservation that states that matter cannot be made or destroyed. He said that matter could be rearranged, but never dissapear. He was known for his experiment in which he converts HgO in Hg+O. -
Berzelius
He introduced a system of chemical systems that used one or two letters abbriviating their latin name. He then created a table of Atomic weights, included that of 43 elements in 1826. -
Avogadro
He clarified the confusion between the difference of a molecule and an atom. He also defined mass and differientiated it from weight. He hypothesized that diferent gases of an equal volume has equal number of molecules. -
Dalton
Dalton came up with the Atomic Theory that states 4 thing:
1) All matter is made of atoms. Atoms are indivisible and indestructable.
2) All atoms of a given element identical in mass and properties.
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangment of atoms. -
Mendeleev
He published his periodic table that arranged the 93 known elements into a system based on their atomic masses. He also grouped them by similar properties, and predicted many new elements and correcting mistaken atomic masses based on his table. -
Becquerel
He created an experiment that proved that some chemical, when composed, let off pentrating rays. He found this out while studying the effect of X-rays on film. -
Planck
He created constant variable H to be used in equations to describe the bahavior of waves and particles at the atomic scale. H represents erg-seconds, which is the amount of energy needed to move a milligram of mass one centimeeter. His variable was used by Bohr to create a more accurate model of the atom. -
M. Curie
She discovered and tested radioactivity electron based on the discoveries of two scientists recent discoveries; Becquerel and Roentgen. She used an instrument created by Pierre, a professor of physics, and his older brother, Jacques which was a new type of electrometer. She used this to test the effects of uranium and the rays it gives off. -
Thomson
He suggested a model of the Atom in which the electrons are suspended in a charged substance. His model became known as the "plum-pudding model" because plum pudding is used to represent the area that the electrons are suspended in. -
Rutherford
Rutherford tested Thomson's Plum-pudding model and created his own in which a positively charged core, the nucleaus is surrounded by a negativley charged substance, the Nuclear Model. -
Bohr
He improved upon Rutherford's model of the atom, finding a problem with the electrons and the movement of them. He proposed a model in which the electrons were confined to a limited area around the nucleas, thus making them more stable than previoulsy thought. -
Moseley
He studied under Rutherford to develope the application of the X-ray to study atomic structure. He used his discoveries to re-construct the periodic table more accuratley. He is the reason the periodic table is organized by atomic number. -
Milikan
By using his oil-drop apparatus, Millikan successfully measured the charge of the electron in water droplets. He used X-rays and gravity in his experiments, along with a positivley charged plate. The droplets that caught X-rays gained electrons and fell more slowly or rose towards the plate. -
Chadwick
While studying radioactivity, Chadwick discovered the positivley charged particle within the ncleus, the proton. At this time, he and many other scientists thought that the proton wasn't the only particle in the nucleus, but they did not know what the other particle was yet. -
Heisenberg
He created a theory that showed that the position and velocity of the elcentron cannot be represented by regular numbers, but instead, by matrices, complex mathematical structures. He also created the principle of uncertainty, which shows errors in the equation involving H that are unnnoticible on the human scale, but should be taken into account when studying atoms. -
Schrodinger
He used the Bohr model to create a mathematical equation that describes the likelyhood of finding an electron in a certain location. This atomic model is known as the Quantum Mechanical Model. -
L. Meitner
She was the first to discover the proccess of atomic fission, or the splitting of the nucleus into pairs of other atomic nuclei. She is hardly recognized for her work and wasn't paid to work. Through her and Hahn's procedure, they thought they had discovered nine new elements.
