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400
380 BC Aristotle
unfortunately, the atomic ideas of Democritus had no lasting effects on other Greek philosophers, including Aristotle.
WHAT: He dismissed the atomic idea as worthless.He developed a theory that was based on the four elements.
How: Aristotle’s theory made a great generalization of all matter of the four elements: fire, water, earth, and air. He also believed that there were four qualities to these elements: dryness, hotness, coldness, and moistness. -
460
460 BC Democritus
Democritus first proposed the existence of an ultimate particle. He asked this question: If you break a piece of matter in half, and then break in half again, how many breaks will you have to make before you can break it no further?
WHAT: He thought that it ended at some point, a smallest possible bit of matter, He called these basic matter particles, ATOMOS meaning ' not divisible' or 'unbreakable'. This was the start of the theory of atom. -
John DALTON
It wasn't until the start of the nineteenth century
WHAT: Start of the nineteenth century that a theory of atoms became linked to strong experimental evidence. He put forward his ideas about atoms. he proposed an "ATOMIC THEORY" with spherical solid atoms based upon measurable properties of mass -
William Conrad Roentgen
Discovered x-rays while using cathode-ray tubes. How: Found that x-rays could pass
through solid objects -
J. J. THOMSON
English scientist J. J. Thomson's cathode ray experiments let to the discovery of the negatively charged ELECTRON an the first ideas of the structure of these indivisible atoms. Thomson proposed the Plum Pudding Model.
In this model, the volume of the atom is composed primarily of the more massive possitive portion. -
Hantaro Nagaoka
Nagaoka developed an early, incorrect "planetary model" of the atom. How: The model was based on the stability of Saturn's rings. -
Ernest Rutherford
Nearly a decade after Thomson, Ernest Rutherford's famous gold foil experiments led to the nuclear model of atomic structure. Ernest Rutherford said one day "hey, I think I will shoot some stuff at atoms." He shot alpha particles at some really thin gold foil. Rutherford found that most of them went right through the foil. -
Niels Bohr
Niels Bohr improved upon Rutherford's nuclar model by explaining that the electrons were present in fixed orbits outside the nucleus.The electrons were confined to specific orbits of fixed radius, each characterized by their own discrete levels of energy. While electrons could be forced from one orbit to another orbit, it could never occupy the space between orbits. The model proposed by Niels Bohr is the one that you will see later. -
Henry Moselery
Moseley's contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. This stemmed from his development of Moseley's law in X-ray spectra. Moseley's Law justified many concepts in chemistry by sorting the chemical elements of the periodic table of the elements in a logical order based on their physics.
How: He did this by providing the first experimental evidence of Niels Bohr's theory. -
Louis de Brogile
What: He developed a theisis of important findings. How: It served as the basis for developing the general theory now known by the name of wave mechanics, a theory which has utterly transformed our knowledge of physical phenomena on the atomic scale. -
James Chadwick
James Chadwick discovered the neutron in 1932. The discovery of the neutron led directly to the discovery of fission and ulimately to the atomic bomb -
Erwin Schrödinger
What: He generated a mathematical model for the distribution of electrons in an atom. How: He combined the equations for the behavior of waves with the Louis de Broglie equation.
