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Period: 460 BCE to 370 BCE
Democritus
He was an ancient Greek philosopher who theorized atoms were specific to the material they composed. -
Period: 427 BCE to 347
Plato
Plato said that the ideal geometric forms were atoms. -
Period: 384 BCE to 322 BCE
Aristotle
He did not believe in the atomic theory and thought everything was made of either earth, air, fire, or water. -
Period: 100 BCE to 800
The Alchemists
They laid don the foundation for the periodic table by proving the existence of atoms. -
Period: to
Lavoisier
He defined the law of conservation mass, which helped shape the atomic theory. -
Period: to
John Dalton
He introduced the atomic theory into chemistry. -
Newland's Law of Octaves
This law said if elements are organized by atomic mass similar atoms will be by each other. -
Period: to
Robert Millikan
He measured the electric chare and did famous work on the photelectric effect. -
Mendeleev's Pd. Table
The periodic table of elements which organizes different elements based off their atomic mass, or number of protons. -
Photoelectric Effect
The emission of electrons when electromagnetic radiation hits something. -
Discovery of Radioactivity
Radioactivity was accidentally discovered when Henri Decquerel opened a drawer with spontaneous radioactivity. -
Discovery of the Electron
Scientist's found the electron while searching for electrical properties of matter in cathode rays. -
Planck's Quantum Theory of Light
This theory says light must be 3,200 Kelvin Degrees so that the energy is visible. -
Plum Pudding Model
A historic model of the atom. -
Charge of the Electron
Robert Millikan used negatively charges oil droplets to measure the charge of an electron. The charge is A~-1.60A~-10-19 coulombs. -
Rutherford's Gold Foil Experiment
He hit gold foil with positively charged particles, which mostly went through. -
Bohr's Planetary Model
In this atomic model electrons travel around the nucleus like planets orbit the sun. -
Moseley's Atomic Numbers
He stated the number of protons is the atomic number. -
Discovery of the Proton
His nuclear research led him to split the atom then he discovered protons. -
Schrodinger Equation
This is an equation that determines the wave function of a quantum-mechanical system. -
Heisenberg Uncertainty Principle
Heisenberg said that we will not be able to know the place and speed of a particle accurately. -
Discovery of the Nuetron
James Chadwick said the core of the atom had an uncharged, or neutral, atom called the neutron.