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340
Aristotle
In 340 BC, Aristotle disagreed with Democritus theory of atoms. He believed that you would end up with a particle that could not be cut. Aristotle believed that matter is made of Earth, fire, air, and water. -
400
Greek Philosopher Democritus
400 BC
Proposed that small particles called Atoms make up all matter. -
John Dalton's Atomic Theory
He published his atomic theory. His theory states: All substances are made of atoms. They are small particles that cannot be created, divided, or destroyed. Atoms of the same element are exactly alike, & atoms of different elements are different. Atoms join with other atoms to make new substances. -
John Dalton
Revised Atomic Theory -
Dmitri Mendeleev
Developed the first periodic table of elements. -
J.J. Thomson
Identifies electrons as particles that are present in every atom. Plum-pudding Model. -
Ernest Rutherford Gold-Foil Experiment
He discovery that most of an atom's mass is located in a dense region now called the nucleus. -
Ernest Rutherford Revised J.J. Thomson's Model
This 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. -
Niels Bohr
Bohr model of the atom
This model shows that electrons are in energy levels. -
Henry Moseley
He determined the number of protons in an atom. This is called the Atomic number. -
Erwin Schrodinger, Werner Heisenberg, & other scientists
They created the Electron Cloud Model. -
James Chadwick
He discovered the neutron, one of the particles in the nucleus of an atom. -
Glenn Seaborg Modern Perodic Table
He devised the Modern Periodic Table. -
Scientists in Switzerland
They developed a scanning tunneling microscope, which is used to see atoms for the first time.
