-
460 BCE
Democritus
Democritus made an ancient atomic theory. He stated that everything is made up of small invisible atoms. -
428 BCE
Plato
Plato made a theory that stated atoms broke down into triangles to form bigger shapes(elements). -
384 BCE
Aristotle
Aristotle said that mixing two substances of comparable amounts are called compounds. -
700
The Alchemists
People who wanted to manipulate the properties of matter to get more valuable substances. -
Lavoisier
Discovered the role of oxygen in combustion. Named the element Hydrogen. -
John Dalton
Stated that all matter is made of atoms which are invisible. -
Newlands law of octaves
Stated that elements organized by increasing atomic weight will have similar chemical and physical properties every 7 elements. -
Robert Millikan
Found the elementary charge of electrons using the oil drop experiment. -
Mendeleev's Periodic Table
He realized elements physical and chemical properties were related to their atomic mass. He then made a table to show this. -
Photoelectric Effect
When electrically charged particles are released from material when it absorbs electromagnetic radiation. -
Discovery of Electron
Scientists were researching cathode rays for electrical properties in matter. -
Planck's Quantum Theory of Light
Says that light bulb filaments should be heated to 3200 kelvin so the energy is emitted as visible waves. -
Plum Pudding Model
The scientific model of an atom. "Plums" were the negative charge inside the "pudding" a positively charged area. -
Charge of the Electron
The electron is the lightest stable subatomic particle known. It has a negative charge of 1.602176634 × 10−19 coulomb. -
Rutherford's Gold Foil Experiment
Gold foil was hit with positively charged alpha particles. Most particles went through the foil proving gold atoms were mostly empty space. -
Bohr's planetary model
Showed that electrons orbit the nucleus. -
Moseley's Atomic Numbers
Stated the atomic number is the number of protons in an atom. -
Discovery of proton
Ernest Rutherford split atoms and discovered the proton. -
Schrodinger Equation
An equation that showed where an electron would be at any given moment. -
Heisenberg Uncertainty Principle
We cant know both the position and speed of the particle. -
Discovery of Neutron
James Chadwick discovered the neutron. He believed alpha particles did not have enough energy to produce powerful gamma rays. He found particles that have the same mass as protons but no charge. -
Discovery of radioactivity
Accidently discovered by Henri Becquerel when studying x-rays.
