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400 BCE
Early Greek Model
Leucippos and Democritus reasoned that if solid matter was cut into halves, eventually the halves would be so small you wouldn't be able to cut it anymore.
They called the smallest piece atmos (Greek for "Uncuttable") -
384 BCE
Alchemy
Aristotle proposed that all matter be made up of proportions of earth, air, fire, and water
Alchemy dominated the chemical landscape for 2 millennia
Important Discoveries during this time: The method of separating metals from ore, this is called Distillation -
Period: to
John Dalton
Came up with the atomic theory which states:
1. Matter is composed of small particles called atoms which cannot be created nor destroyed
2. Atoms of elements are identical to each other and different from other elements
3. Compounds are formed by a combo of 2 or more different atoms
4. In a chemical reaction there is a rearrangement of atoms
His theory is still applied in science today but is more in-depth
Ex: Atoms can be broken in a nuclear reaction not in a chemical reaction -
Period: to
Henri Becqueral
1896 he discovered natural radioactivity
Earliest work involved polarization of light
Realized rays from uranium salts causes gases to ionzie (where different from X-rays in that X-rays could be deflected by electric or magnetic fields)
Nobel Prize in physics in 1903 -
Period: to
John Joseph (J.J.) Thompson
Modified the crookes tube, passing a cathode in the anode resulting in a narrow ray concentrated on a fluorescent target.
Calculated the change - mass ratio for cathode ray particles. 1.76 x10^8 C/g
Discovered mysterious negative particles in atoms by experimenter with different metals and gas
Nobel prize for identifying Cathode Rays as electrons
Proposed the Plum Pudding atomic model -
Period: to
Marie and Pierre Curie
Discovered Radium and Polonium
Pierre discovered the phenomenon of piezoelectric
Marie discovered that pitchblend (an ore) contained small amounts of an unknown element
Nobel Prizes with Henri Becquerel with the discovery of radioactivity -
Period: to
Ernest Rutherford
Came up with how radio activity worked (Discovered Alpha, Beta, and gamma rays)
Hypothesized that the middle of an atom had a dense positive mass called the "nucleus"
His model of an atom resembled a planetary with the nucleus in the middle and electrons circling it
In 1908 won the Nobel Prize for his contribution to the atomic structure -
Period: to
Niels Bohr
Came up with how radio activity worked (Discovered Alpha, Beta, and gamma rays)
Hypothesized that the middle of an atom had a dense positive mass called the "nucleus"
His model of an atom resembled a planetary with the nucleus in the middle and electrons circling it
In 1908 won the Nobel Prize for his contribution to the atomic structure -
Period: to
James Chadwick
Worked with Rutherford in the transmutation of light element by bombarding them with alpha particles
1932 proved the existence of neutrons which allowed for the fission of Uranium-235, this allowed for the creation of the atomic bomb
Won the Nobel Prize in 1935 and was Knighted in 1945