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400 BCE
Democritus
Democritus was an Ancient Greek pre-Socratic philosopher from Abdera, people from today he is remembered for his formulation of an atomic theory of the universe. -
387 BCE
Plato
Plato was a Greek philosopher born in Athens, during this time period in Ancient Greece. He founded the Platonist school of thought and also the Academy. -
334 BCE
Aristotle
Aristotle was a Greek philosopher during this time period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of philosophy. -
500
The Alchemists
The alchemists believed that all metals were formed from two things. Mercury and sulfur. The mercury gave rise to the metals. The sulfur, with its essential property of combustibility, (rusting) -
Lavoisier
Antoine Lavoisier was a French nobleman and chemist. Had a large influence on both the history of chemistry and the history of biology. -
John Dalton
John Dalton was an English chemist, physicist and meteorologist. He is best known for introducing the atomic theory into chemistry, -
Newland's Law of Octaves
Made by the English chemist J.A.R. If the chemical elements are arranged according to increasing atomic weight, those with similar physical and chemical properties occur after each interval of seven elements -
Mendeleev's Pd. Table
Mendeleev made the law that the periodic “Element properties are a periodic function of their atomic weight.” Mendeleev placed elements in the order of their atomic weights. -
photoelectric effect
photoelectric effect, phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation. -
Discovery of Radioactivity
Henri Becquerel Discovers Radioactivity. In March 1896, French physicist Henri Becquerel opened a drawer and discovered spontaneous radioactivity. It was a accident -
discovery of the electron
During the 1880s and '90s scientists searched cathode rays for the carrier of the electrical properties in matter. -
Charge of the electron
An electron is a negatively charged subatomic particle that can be either bound to an atom or free. Together, electrons, protons and neutrons form an atom's nucleus. -
plum pudding model
The plum pudding model is a historical scientific model of the atom. The plum pudding model is defined by electrons surrounded by a volume of positive charge.l -
Planck's quantum Theory of Light
Planck's quantum theory of light tells us that light bulb filaments should be heated to a temperature of about 3,200 Kelvin to ensure that most of the energy is emitted as visible waves. If it was any hotter, we would start to TAN. -
Robert Millikan
Robert Andrews Millikan was an American experimental physicist honored with the Nobel Prize for Physics in 1923 for the measurement of the elementary electric charge and for his work on the photoelectric effect. -
Rutherford's gold foil experiment
A piece of gold foil was hit with alpha particles, which have a positive charge. Most alpha particles went right through. This showed that the gold atoms were mostly empty space. -
Bohr's Planetary Model
The Bohr Model is a structural model of an atom. In this model, the electrons travel around the nucleus of an atom in distinct circular orbits, or shells. -
Mosley's Atomic numbers
Moseley published a paper in which he concluded that the atomic number is the number of positive charges in the atomic nucleus. He also stated that there were three unknown elements, with atomic numbers 43, 61, and 75, between aluminum and gold. -
Discovery of the Proton
The proton was discovered by Ernest Rutherford. During this period, his research resulted in a nuclear reaction which led to the first 'splitting' of the atom, where he discovered protons. -
Schrodinger Equation
The Schrödinger equation is a linear partial differential equation that governs the wave function of a quantum-mechanical system. -
Heisenberg uncertainty principle
Formulated by the German physicist and Nobel laureate Werner Heisenberg in 1927, the uncertainty principle states that we cannot know both the position and speed of a particle, such as a photon or electron, with perfect accuracy. -
Discovery of the neutron
James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron.
