Atomic Structure

Events

Democritus

460 BC - 370 BC

He formed the atomic theory of the universe
The original atomic theory stated that “The universe is composed of two elements: the atoms and the void in which they exist and move.” Democritus believed that atoms were "minuscule quantities of Matter"

Aristotle

384 BC - 322 BC

-He tutored Alexander the Great

-Aristotle’s research in the sciences included a study of biology.

-He was the author of a scientific system that was the backbone to both Christian Scholasticism and medieval Islamic philosophy.

-He was the founder of formal logic

Alexander The Great

332 BC

He took over Egypt and Greek philospers were interested in the Egyptian religion. Greek views on matter were merged with the religion, resulting in "Khemia"

Alchemy

300 BC

Definition: A medieval chemical science and speculative philosophy aiming to achieve the transmutation of the base metals into gold, the discovery of a universal cure for disease, and the discovery of a means of indefinitely prolonging life

Alchemy was practiced in Mesopotamia, Ancient Egypt, Persia, India, Japan, Korea and China, in Classical Greece and Rome, in the Muslim civilizations, and then in Europe up to the 19th century

Further Developement

600 AD

The Arabs helped Egypt further developed the science of "Khemia", spreading it to the West in the 700's

The Phlogiston Theory

1667

The phlogiston theory is a superseded scientific theory that postulated that a fire-like element called phlogiston is contained within combustible bodies and released during combustion. ... The theory attempted to explain burning processes such as combustion and rusting, which are now collectively known as oxidation.

Was stated by Joachim Becher.

Anton Laurent de La Voisier

1743 - 1794

He is he Father of Modern Chemistry. He discovered the Law of Conservation of Mass. Was beheaded during The French Revolution. He dispelled the Phlogiston Theory by proving oxygen causes combustion.

Benjamin Franklin

1752

Discovered that electrical charges come in 2 varieties: positive and negative.
Like charges repel, opposite charges attract.

He was a major figure in the history of physics.

Joseph Louis Proust

1754

He was a French Chemist who discovered The Law of Definite Proportions, or The Law of Constant Composition. This law states that a chemical compound always contains exactly the same proportion of elements by mass.

John Dalton

1766 - 1844

John is the Father of Atomic Theory.
His Atomic Theory of Matter:
- Matter is made up of atoms that are indivisible and indestructible.
-All atoms of an element are identical (not true in today's science)
- Atoms of different elements have different weights and different chemical properties.
- Atoms of different elements combine in simple whole numbers to form compounds.
- Atoms can not be created nor destroyed. When a compound decomposes, the atoms are recovered unchanged.

William Crookes

1875

Cathode Ray Tube (CRT):
-(CRT) is a specialized vacuumtube in which images are produced when an electron beam strikes aphosphorescent surface

-Paddle wheel placed in CRT:
When Crookes placed a wheel into the CRT, and turned on the battery, the wheel spun. Since the tube was evacuated, this told Crookes that the Crhode Ray has mass.

Sir John Joseph Thomson

1898

He continued experimenting on the CRT

JJ Thomson used charged plates to deflect the cathode ray. Found the ray deflected away from the negative plate, and toward the positive.
Sir John named the negative particles, electrons.

Ernest Rutherford: Classification of Radiation"

1900

Ernest Rutherford postulated the nuclear structure of the atom, discovered alpha and beta rays, and proposed the laws of radioactive decay. He received the Nobel Prize in Chemistry in 1908.

Becquerel

1903

Discovered radioactivity in Uranium ore.

  • One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second

Curies (Marie and Pierre

1903

Pierre Curie was a french physical chemist, cowinner with his wife Marie Curie of the Nobel Prize for Physics in 1903. He and Marie discovered radium and polonium in their investigation of radioactivity.

Marie Curie the first woman to become a professor at the University of Paris, and in 1995 became the first woman to be entombed on her own merits in the Panthéon in Paris.

Millikan

1910

Robert Andrews Millikan was an American experimental physicist honored with the Nobel Prize for Physics in 1923 for the measurement of the elementary electronic charge and for his work on the photoelectric effect.

Famous Gold Foil Experiment

1910

~ Stretched a sheet of gold foil in a tin can and coated the inside of the can with fluorescent paint.
~ Aimed a ray of alpha radiation (+ charges) at the foil.
~ Expected that the alpha rays would pass right through the metal atoms in the foil, and the fluorescent coating would light up right behind the foil.

What he observed:
- 99.9% of the time, the ray lit up the can right behind the foil.
- .1% of the time, the ray lit up the can OPPOSITE the foil. (behind the alpha source)
- This told him that the ray had hit something massive and dense in the center of the atom.

Earnest concluded that:.
A. Atoms are mostly empty space.
B. There must be a solid core in the center of the atom.
C. The core must be positively charged, since it deflected an alpha ray.

James Chadwick

1935

 Proved the existence of another subatomic particle, that had no charge, named it the neutron.

  • He was the head of the British team that worked on the Manhattan Project during the Second World War.

  • He inspired the U.S. Government to start serious research in atomic bombs.