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400 BCE
Democritus Adopts the Atomic Theory
The atomic theory originally came from his mentor, Leucippus, but was then adopted by Democritus. The atomic theory states that "the atoms and the void where they exist and move, are the only two components of the universe." According to Democritus, atoms were "miniscule quantities of matter." -
Dalton Introduces the Modern Atomic Theory
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Specific month and day not available.
The Modern Atomic Theory states:
1) All matter is made of atoms
2) Atoms are indivisible and indestructible
3) Compounds are formed by a combination of 2+ different kinds of atoms -
JJ Thomson Discovers The Electron
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Specific month and day not available.
Thomson discovered the electron when he experimented with a Crookes. A Crookes is considered a "cathode ray." He also discovered that cathode rays were negatively charged. Doing this helped Thomson pursue innovations in atomic structure exploration. -
Albert Einstien and His Famous Equation
In 1905, Albert Einstein formulates Special Theory of Relativity.
This theory determined that the laws of physics are the same for all non-accelerating observers. It also showed that the speed of light in a "vacuum" is the same no matter the speed the observer is at. Einstein established the Law of Mass-energy equivalence using his famous formula(E=mc²). -
Millikan Determines Electron Unit Charge
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Specific month and day not available.
Millikan determined the unit charge of the electron using his oil drop experiment. This allowed him to calculate the mass of an electron and the positively charged atoms. His equation was e = 1.60 x 10-19 coulombs. -
Rutherford Discovers the Nucleus
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Specific month and day not available.
Atoms have a small charged nucleus that is surrounded by empty space, and are circled by tiny electrons. This became the Rutherford Model, or the Planetary Model. -
Bohr Proposes His Hydrogen Theory
(DO NOT REGARD TO THE TIMELINE'S DATE) Specific month and day not available.
Niels Bohr proposed a theory for hydrogen atom using the quantum theory. This theory states:
1) Energy is transferred only in certain well-defined quantities. 2)Electrons should move around the nucleus but only in prescribed orbits.
3)When jumping from one orbit to another with lower energy, a light quantum is emitted. -
Heisenberg and His Theory of Quantum Mechanics
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Specific month and day not available.
Werner Heisenberg is best known for his uncertainty principle and theory of quantum mechanics that he published in 1925. Heisenberg showed that the neutron could not be an electron-proton pair, and was actually a new "straightfoward" particle using Chadwick's research. -
Schrodinger and the Quantum Mechanical Model
(DO NOT REGARD TO THE TIMELINE'S DATE) Specific month and day not available.
Erwin Schrodinger enhanced the Bohr atom model in 1926. He Used math equations to describe how likely it is to find an electron in a specific position, which was known as the Quantum Mechanical Model of an atom. -
Chadwick Discovers the Neutron
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Specific month and day not available.
In 1930 James Chadwick discovered that beryllium, when debunked by alpha particles, it emitted a very energetic stream of radiation (This was believed to be gamma radiation).
Chadwick also Invented the Geiger Counter to detect and measure radiation.
