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400
Democritus
-Scientest primarily responsible, Democritus.
-Born in Greace in 460 B.C. & lived to be 90 years old dying in the year 370 B.C,
-400 B.C.
-The atomic theory stated that "The Universe is composed of two elements:the atoms and the void in which they exist and move"
-His Hypothisis was created in 465 B.C. -
John Dalton
-Born 1776-1844
-Daltons theory :1.Matter is composed of small particles called atoms.
2.All atoms of an element are identical, but are different from those of any other element.
3.During chemical reactions, atoms are neither created nor destroyed, but are simply rearranged
4.Atoms always combine in whole number multiples of each other
-Atomic symbols. -
Ernest Rutherford
-His atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons.
-His model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space.
-Discovered the proton.
-His experiment involved the firing of radioactive particles through minutely thin metal foils and detecting them using screens coated with zinc sulfide. -
Aristotle
-He developed a theory that ws based on the four elements, Fire,Earth,Water, & Air.
-Also believed that there were ffour qualities to these elements : dryness, hotness, coldness and moistness. -
Henri Becquerel
- Born in 1852-1908 -discovered that a sample of uranium was able to expose a photographic plate even when the sample and plate were separated by black paper. -Also worked with Marie & Pierre Curie
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J.J. Thomson
-Born 1856-1940
-Performed experiments with cathode ray tubes.
-cathode ray tube is an evacuated tube that contains a small amount of gas between two metallic plates.
-When a potential is placed between the cathode (the negatively charged plate) and the anode (the positively charged plate) a "ray" of electric current passes from one plate to the other. Thomson discovered that this ray was actually composed of particles.
-After many experiments they became known as electrons. -
Robert Millikan
-Born on march 22, 1868
- Conducted the Oil Drop Experiment
-Determined the charge on electrons. -
Niels Bohr
-Born 1885-1962
-The Bohr Model is probably familar as the "planetary model"
-Modification of the earlier Rutherford Model, some people call Bohr's Model the Rutherford-Bohr Model.
-The Bohr Model has an atom consisting of a small, positively-charged nucleus orbited by negatively-charged electrons. -
Quantum model
- Its' model of the atom explains its stability and like Bohr's Model, treats atoms as electrons surrounding a nucleus. -combonations of all theories. -The quantum model is a probability area an electron may be located in. -The Quantum model also includes a nucleus containing neutral particles known as a neutrons and positive particles called protons.
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James Chadwick
- Born October 20,1891 & died onJuly 24,1965
- He discovered the third elemantry particle of the atom, the neutron, which is in the necleus along with protons. -Inspired other scientists
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Marie & Pierre Curie
-Substances and elements are made up of small units called atoms. Matter could be subdivided into these fundamental units and no further.
-Did considerable work in the investigations of radioactivity. Marie is the first woman to win a Nobel Prize. They discovered two new elements: Polonium and Radium - the latter named for the radioactive glow visible in the dark.
-thought the Atom looked as though it was a planet with many electron rings around them.
