-
400
Leucippus (480-420 BCE)
Proposed that matter is composed of atoms seperated by space through which the atoms move. Also suggested that properties of matter reflect the properties of the atoms that compose it. -
401
Empedocles (450 BCE)
Proposes theory that changes in matter are due to changes in indivisible particles. Also seperates matter into four elements: earth, water, fire, and air. Believes that matter is the principle of all things and that different ratios of the four elements make up all matter. -
402
Parthenon is completed (432 BCE)
The Parthenon construction is completed in Athens, Greece. -
403
Democritus (420 BCE)
Introduced his ideas of matter: All matter is made up of atoms; All matter is eternal and indivisible; Atoms are so small they they can't be divided; There is empty space between atoms; Different types of atoms vary in shape and size. -
404
Plato (428-348 BCE)
Plato introduces the belief that matter is made up of five fundamental solids. Also belives in five elements: earth, water, fire, air, and aether. -
405
Aristotle (384-322 BCE)
Aristotle agrees with many of Plato's proposals and ideas. He also originates the idea of aether (heavens, stars, and planets) -
John Dalton: Law of Multiple Proportions
Introduces the Law of Multiple Proportions which states "If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers." -
John Dalton: Atomic Theory
Dalton's Atomic Theory consists of 5 key components: 1) All matter is made of atoms. 2) Atoms of a given element are identical in size, mass, and chemical properties. 3) Atoms of different elements have different masses and properties. 4) Compounds are formed by a combination of two or more different kinds of atoms. The elements combine in simple, whole-number ratios. 5) Atoms cannot be subdivided, created, or destroyed. But can be combined, seperated, or changed in the way they are arranged. -
Louisiana Purchase
Thomas Jefferson purchases 828,000 square mile piece of land from France. -
Emancipation Proclamation
Abraham Lincoln proclaims the freedom of more than 3/4 of the slaves enslaved in the United States at the time. -
Thomson: Discovers electron
J.J. Thomson discovers the presence of the electron in an atom during his Cathode Ray Tube Experiment. -
Thomson: Plum Pudding Model
J.J. Thomson develops the plum pudding atomic model that shows protons and electrons evenly mixed together. -
Rutherford: Discovery of Alpha particles
Ernest Rutherford discovers radioactive particles that he names "Alpha" and "Beta" particles after performing various studies based on radiation. -
Planck: Quantum Theory
Max Planck develops the quantum theory which states that energy is released and absorbed by atoms in certain fixed amounts known as quanta. -
Thomson: Alpha ray discovery
J.J. Thomson discovers alpha rays are heavily positively charged particles. -
Thomson: Nobel Prize
J.J. Thomson wins the Nobel Prize in Physics. -
Rutherford: Gold Foil Experiment
Ernest Rutherford discovers that atoms have a dense center with orbiting electrons while performing his infamous experiment that used gold foil and alpha particles. -
Rutherford: Nobel Prize
Ernest Rutherford wins the Nobel Prize in Chemistry. -
Rutherford: Mass of an atom
Ernest Rutherford discovers that the mass of an atom comes from a positively charged ball at the center of an atom. -
Millikan: Oil-drop experiment
Robert A. Millikan performs his oil-drop experiment and finds that electrons have a negative charge. This experiment also allows hims to find the mass of an atom. -
Bohr: Energy shells
Niels Bohr finds that electrons move around nucleus in successively large orbits. -
Discovery of King Tut's Tomb
Archaeologist Howard Carter discovers the tomb of King Tutankhamun in Egypt. -
Millikan: Nobel Prize
Millikan wins the Nobel Prize in Physics. -
Louis de Broglie: Wave Discovery
Louis de Broglie discovers that atoms can perform as waves under some conditions. -
Heisenberg: Matrix Mechanics
Werner Heisenberg develops matrix mechanics which explains behaviors of atoms. -
Schrodinger: Quantum Mechanics
Schrodinger develops quantum mechanics. This eventually lead to the quantum mechanic atomic model, which is the most recent atomic model. It suggests that there are orbitals (electron clouds) which is where there is likely to be an electron. This theory is based on probability, not certainty. -
Heisenberg: Uncertainty Principle
Werner Heisenberg develops the Uncertainty Principle which states "It is impossible to determine with perfect accuracy both the position and momentum of a particle at any given point in time." -
Louis de Broglie: Nobel Prize
Louis de Broglie wins Nobbel Prize in Physics. -
Schrodinger: Wave Equation
Schrodinger creates the wave equation and determines that electrons are in a continuous cloud. -
Chadwick: Discovery of the Nuetron
Chadwick discovers the nuetron and that it is nuetrally charged. -
Heisenberg:Studies Electromagnetic Field
Werner Heisenberg studies the electromagnetic field and observes that charged particles bounce photons of light between them. -
Heisenberg: Nobel Prize
Werner Heisenberg wins the Nobel Prize in Physics. -
Schrodinger: Nobel Prize
Schrodinger wins the Nobel Prize in Physics. -
Chadwick: Nobel Prize
James Chadwick wins the Nobel Prize in Physics. -
First Atomic Bomb is dropped
The first atom bomb is dropped on Hiroshima, Japan in the midst of World War II
