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427 BCE
Plato
Plato was a Greek philosopher who introduced atomic theory which is ideal geometric forms serve as atoms. -
400 BCE
Democritus
Democritus was a Greek philosopher who theorized that all material bodies are made up of invisibly small "atoms". -
332 BCE
Aristotle
Aristotle was a Greek Philosopher who thought that all things on earth were not made of atoms, but instead made of the four elements of water, fire, earth, and air. -
The Alchemists
Alchemists were people who were well versed in the knowledge of alchemy. They contributed to atomic theory by laying down the foundation of modern day periodic table of the elements. -
Lavoisier
Lavoisier was a French chemist who discovered that matter was composed of atoms and that it could not be created nor destroyed during chemical reactions. -
John Dalton
John Dalton was an English chemist who created the theory that each element has its own unique kind of invisible atom. -
Newland's Law of Octaves
In law of octaves, if the chemical elements are arranged according to increasing atomic weight, those with similar chemical and physical properties occur after each interval of seven elements. This was discovered by and English chemist named John Newlands. -
Mendeleev's Pd. Table
Mendeleev's Pd. Table was made by a Russian chemist named Dimitri Mendeleev. He did this by making a set of cards of the elements, writing down the element's name, atomic mass, and other properties and rearranged them in many different ways looking for a pattern. -
Photoelectric Effect
The Photoelectric Effects was made by a German physicist named Heinrich Rudolf Hertz. He did this by shining an ultraviolet light on electrodes that caused a change in the voltage between them. -
Discovery of Radioactivity
Radioactivity was discovered by a French engineer named Henri Becquerel. Becquerel discovered radioactivity when he was working with phosphorescent materials. He placed uranium salts on top of a photographic plate and wrapped it in black paper. The salts caused a blackening of the plate despite there being a sheet of paper between them. -
Discovery of the electron
The electron was discovered by a British Physicist named J. J. Thomoson. He discovered electrons when he was experimenting with Crookes, or cathode ray, tube. -
Planck's Quantum Theory of Light
Planck's Quantum Theory of Light was made by a German physicist named Max Planck. He made this theory by conducting many physical experiments. -
Plum Pudding Model
The Plum Pudding Model was made by a British Physicist named J. J. Thomoson. The model depicted electrons as negatively charged particles embedded in a sea of positive charge. -
Rutherford's Gold Foil Experiment
The Gold Foil Experiment was conducted by a New Zealand physicist named Earnest Rutherford. He shot a beam of particles at a sheet of gold foil and a few of the particles where deflected. -
Robert Millikan
Robert Millikan was an American physicist who made an accurate determination of what kind of charge an electron had. He did this by using what is known as "The falling-drop method". -
Bohr's Planetary Model
Bohr's Planetary Model was created by a Danish physicist named Neils Bohr. Bohr's model demonstrates electrons circling the nucleus of the atom in specific paths called orbits. -
Mosley's Atomic Numbers
Mosley's Atomic Numbers were made by an English physicist named Henry Mosley. He did this by observing and measuring the X-ray spectra of various chemical elements using diffraction in crystals. -
Discovery of the proton
Protons were discovered by a New Zealand physicist named Earnest Rutherford. Rutherford discovered the proton when he was conducting research which resulted in a nuclear reaction that led the the first "splitting" of the atom, which is were he discovered protons. -
Charge of the Electron
The charge of an electron was discovered by an American physicist named Robert Millikan. He discovered the charge by doing what is known as the oil drop experiment. He did this by using negatively charged oil droplets. -
Schrödinger Equation
Schrödinger Equation was made by an Austrian physicist named Erwin Schrödinger. He made the equation by using mathematical equations to describe the likelihood of finding an electron in a certain position. -
Heisenberg Uncertainty Princple
The Heisenberg Uncertainty Principle was made my a German physicist named Werner Heisenberg. This principle was made when he wanted to try to measure the position of an electron with a gamma ray microscope. -
Discovery of the Neutron
The neutron was discovered by a British physicist named James Chadwick. He discovered it by bombarding beryllium with particles from the natural radioactive decay of polonium.