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460
Democritus
-Matter is created by atoms.
-Proposed the existence of an ultimate particle.
- Atomic theory states that atoms are indivisible.
- Lead to the idea of atoms in a void. -
500
Aristotle
-Aristotle said matter was created by four elements; fire, earth, air, and water.
-He didn't think atoms could be in constant motion in a void.
- Four qualities: dryness, hotness, coldness, and moistness.
-First to come up with the idea of the atom and said it was the only thing that could not be split. Was proven wrong with the atom splitting power of the nuclear bomb.
-There were of course no experimental means available to test. -
John Dalton
- Discovered the atomic theory 1803 that states all matter is made up of atoms. -All atoms of a given element are identical in mass and properties. -A chemical reaction is a rearrangment of atoms. -Father of atomic theory. -Experiment: Assigned a relative atomic weight of one to hydrogen and developed a relative atomic weight scale from percent composition data and assumed atomic ratios
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JJ Thomson
-Discorvered the electron.
-"Plum Pudding" Model.
- He claimed that the model of an atom was a sphere of positive matter where electrons are positioned by electrical force.
- Stated that the electron was a component of all matter and calculated the charge to mass ratio for the electron.
- Volume of the atom is composed primarily of the more massive (larger) positive portion (plum pudding).
- Smaller electrons are scattered throughout the positive mass to maintain charge neutrality. -
Maire and Pierre Curie
-Finding out the way to get the atomic mass of an atom.
-Helped Henri Becquerel with his discovery of radioactivity between 1898 and 1902.
- Thought the Atom looked as though it was a planet with many electron rings around them. -
Henri Becquerel
-Received the Nobel Prize for Physics.
- He was ideally suited to answer. -He had studied the phosphorescence of some uranium compounds in particular. -
Ernest Rutherford
-Golf foil equitment.
-Experiment involved the firing of radioactive particles through minutely then metal foils and detecting them using screens coated with zinc sulfide.
-Referred to the hydrogen nucleus as a proton.
-Proposed the existence of the third atomic particle, the neutron.
-Discorvered the neculeous. -
Robert Millikan
-Determined the unit charge of the electron.
- Allowed the calculation of the mass of the electron and the positively charged atoms.
-Formula: e = 1.60 x 10 to the -19th power coulombs.
- Discovered that the weight of an electron is 1836 times smaller than that of a hydrogen atom (atomis mass of 1)
-Discorvered the charge and the mass on an electron. -
James Chadwick
-As they studied atomic disintegration, they kept seeing that the atomic number was less than the atomic mass.
-Since electrons have almost no mass, it seemed that something besides the protons in the nucleus were adding to the mass.
-Discorved the netron.
-One leading explanation was that there were electrons and additional protons in the nucleus as well -- the protons still contributed their mass but their positive charge was canceled out by the negatively charged electrons. -
Quantum Model
-The quantum model is a probability area an electron.
-The Quantum model also includes a nucleus containing neutral particles known as a neutrons and positive particles called protons.
-This protron-electron model accounts for the whole number rule for isotopes masses and is consistent with the emission of alpha (He) and beta (electron) particles. -
Niles Bohr
-The Bohr Model is an approximation to quantum mechanics that has the virtue of being much simpler.
the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun.
-Plantiary Model, electrons orbit the neculeus just like pplants orbit the sun
-the Bohr Model of the atom ultimately arises because the attractive gravitational force in a solar system.
