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Democritus
Democritus's theory was all matter consistsof atoms.
Atoms are solid but invisible.
Atoms are indivisible.
Atoms are homogenous.
Atoms differ in size, shape, mass, position, and arrangement. -
400
Aristotle
Aristotle came up with his model around 400 BC.
Said that there was four elements, fire, air, earth, and water and they are the basic elements of life.
No expierment. -
John Dalton
John Dalton believed all matter is made of atoms and atoms are indestructible.
He also believed compounds are formed by a combination of two or more different kinds of atoms.
Through reasoning and experimentation, he made an interesting discovery. His findings led him to hypothesize that elements combine at the atomic level in fixed ratios. This ratio would naturally differ in compounds due to the unique atomic weights of the elements being combined. -
Henri Becquerel
Henri Becquerel conducted an experiment which started with the exposure of a uranium-bearing crystal to sunlight. Once the crystal had sat in the sunshine for a while, he placed it on a photographic plate. Becquerel theorized that the absorbed energy of the sun was being released by the uranium in the form of x-rays.
He discovered radioactivity. -
Robert Millikan
Robert Millikan has a theory with electrons.
He proved electrical charge, which is carried by an electron.
Millikan performed an experiment based on an Thomson's earlier attempt, but used charged oil drops instead of charged water drops. -
Ernest Rutherford
Ernest Rutherford proved that the nucleus was positive, empty space, and dense. He also discovered the proton as well. His expierement was called the gold foil expierement. -
J.J Thomson
He discovered the electron and his expeirement was called "Plum Pudding". Thomson attempted an experiment where he observed the behavior of falling charged water drops. This experiment, was inaccurate because the water drops evaporated during the experiment, and Thomson could only estimate how fast they evaporated in order to interpret the results.
Robert Millikan changed Thomson's throury by using oil doprs instead of water so it didn't evaporate as quickly. -
Neils Bohr
Bohr's model was known as the "plantetary model"
In the Bohr Model the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun. -
Quantum Model
The quantum theory is the most up-to-date theory of the times. Its' model of the atom explains its stability and like Bohr's Model, treats atoms as electrons surrounding a nucleus. The electrons, however, do not have a planetary orbit.
Electrons are like waves. -
James Chadwick
He dicovered the neutron and he focused on radioactivity to discover his theory. He noticed the atomic number was lower than the atomic mass. -
Marie and Pierre Curie
They discovered polonium and radium.
