AQUINO, Melchizedek

HISTORY OF ATOM - Timeline

Events

Leucippus

500 B.C.E

A Greek Philosopher who develop the Theory of Atomism, the concept of everything is composed of stoms

Democritus

430 B.C.E

Proposed an Atomic Theory (along with his mentor Leucippus) which states that all atoms are small, hard, indivisible and indestructible particles made of a single material formed into different shapes and sizes. He called it "Atomos"

John Dalton

1803

Proposed an Atomic Theory which states: First, all matter is made up of tiny indivisible and indestructible atoms. Second, atoms of the same element are the same. Third, atoms of different elements are different. And finally, atoms combine in whole number ratios to form compounds.

J.J. Thomson

1897

Used cathode rays to discover the electron. Measured the bending of the rays to determne the charge to mass ratio of the electron, modified cathode ray tubes were used to discover the positively charged proton

Albert Einstein

1905

Photoelectric Effect: when light of a certain frequency shines on a metal, electrons are emitted.

Ernest Rutherford

1911

Studied substances, especially alpha particles. Conducted the gold-foil experiment, which determined that the atom is mostly empty space, with a very small, positive nucleus.

Niels Bohr

1913

improved upon the atomic model by trying to answer the question: why aren't electrons pulled into the nucleus?

electrons travel in definite energy levels without radiating energy; electrons in each orbit have a certain amount of energy; energy increases as distance from nucleus increases; electrons lose energy by dropping energy levels

Victor de Broglie

1924

He developed his Theory of electron waves which described the behavior and properties of an object that varies in time or space.

Erwin Schrodinger

1926

Schrodinger's Wave Equation
-treat the electron like a wave
-developed an equation used to determine the probability of finding the electron in any given place around the nucleus
-solutions to the equation are quantum numbers

Werner Heseinberg

1927

Heisenberg published his Uncertainty Principle, which states that it is impossible to know the exact location and velocity of a particle at a given time.

James Chadwick

1932

Discovered the existence of neutrons.

Otto Hahn, Lise Meitner and Fritz Strassmann

1932

They discover Uranium fission.