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800 BCE
The Alchemists
Alchemy, the predecessor of modern chemistry, has influenced the discovery of several scientific concepts and experimental methodologies that have constructed the foundational basis of empirical science. Alchemy had roots in philosophy, astronomy, and religion. -
427 BCE
Plato
Plato is the first person to develop the concept of an atom -
400 BCE
Democritus
Democritus believed that atoms were uniform, solid, hard, incompressible, and indestructible and that they moved in infinite numbers through empty space until stopped. Differences in atomic shape and size determined the various properties of matter. -
384 BCE
Aristotle
Aristotle thought that proper mixing could occur when substances of comparable amounts are brought together to yield other substances called compounds -
lavoisier
Lavoisier did an experiment where he reacted oxygen with inflammable air, obtaining water -
John Dalton
John Dalton said "All matter is composed of extremely small particles
called atoms -
Newlands Law of Octaves
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
he did an experiment of a system of elements based on their atomic weight and chemical similarity -
photoelectric effect
which eclectically charged particles are released from o within a material when it absorbs electromagnetic radiation -
discovery of Radioactivity
Radioactivity demonstrated that the atom was neither invisible nor immutable -
discovery of the electron
an electron is an atom with a negative charge that can be either bound with an atom or free -
Planck's Quantum theory of light
Planck's quantum theory of fussy 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. -
Plum pudding model
a historical scientific model of an atom -
charge of electron
a fundamental physical constant that is used to express the natural occurring unit -
Robert Millikan
Robert Millikan had an atomic theory major success was the accurate determination of the charge carried by an electron, using the elegant falling drop method -
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. -
Bohr's Planetary model
the electrons travel around the nucleus of an atom in distinct circular orbits, or shells. The model is also referred to as the planetary model of an atom. -
Mosley's Atomic Numbers
henry mosley discovered a systematic relation between wave- length and atomic number. He also stated that there were three unknown elements, with atomic numbers 43, 61, and 75, between aluminum and gold. -
Discovery of the proton
A proton is one of three main particles that make up the atom. Protons are found in the nucleus of the atom. This is a tiny, dense region at the center of the atom. Protons have a positive electrical charge of one (+1) and a mass of 1 atomic mass unit (amu), -
Schrodinger equation
A partial differential equation that governs the wave function of a quantum mechanical system -
Heisenberg Uncertainly Principle
Nobel laureate Werner Heisenberg states that we cannot know both the position and the speed of an particle -
discovery of the neutron
James Chadwick announced that the core also contained a new uncharged particle it is now called the neutron