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Democritus 460-370 BC
Democritus is the first to discover the existance of an ultimate particle. He used the word 'atomos' to describe it. He believed that atoms of different substances varied in size and shape. For example, atoms of solids would be triangular and medium sized, whereas atoms of liquids would be big and round. This theory would help explain the hard, soft, fluid, etc, characteristics of different substances. He also claimed that atoms are always in constant motion -
Oct 4, 600
600 BC Aristotle
Aristotle believed that there was only four elements: earth, air, fire and water. He agreed somewhat with Democritus, in that there was a smallest part of matter, but not completely. He believed that only these four elements make up everything else, and through strong disagreement and heavy pushes of his idea, the topic of the atom became somewhat tiresome and people lost interest. -
Joseph Proust's Law of Constant Composition
Proust's law was very radical at the time and not widely accepted. It stated that the composition of a substance is always the same, regardless of where it was found or how it was made. -
John Dalton's Discovery!
John Dalton came up with an atomic theory that consists of four main postulates. The first one held that all matter consists of tiny particles. In agreance with Democritus, his second postulate claimed that atoms are unchangeable and indestructable. In his third point, he says that characterized by the mass of their atoms. Lastly, he claimed that when Elements react, their atoms combine in simple, whole-number ratios. -
Henri Becquerel Discovers Radio Activity!
In 1896, Becqerel found out that Röntgen had discovered that x-rays excite fluorescence in certain substances, and decided to start testing whether or not certain substances gave off rays similar to x-rays. He used uranium salt to do so and through a series of test he had enough information to prove that yes, indeed, radioactivy does exist. The type of radioactivity he discovered is known as beta-ray activity. -
JJ Thompson's Discovery of the Electron
JJ Thompson discovered that all matter contains particles of the same kind that are much smaller than atoms. These particles became known as electrons, which he originally called corpuscles. He then when ton to make a model of the atomic structure, which is sometimes described as the plum pudding model (see picture). It is a circle that holds positively charged particles (which he did not know as protons), and electrons in the middle. -
Max Planck Discovery!
In this year, Max Panck discovered the Quantum Theory! Using mathmatical foundations, he showed that light must be emitted and absorbed is small amounts to correctly describe observed phenomena.Einstien then used this disovery to to show that the energy of ejected electrons was dependent upon the frequency of incident light. Thus the equation, E=hf. -
Ernest Rutherford's Discovery
Ernest Rutherford published his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. He also suggested that most of the atom's mass comes from the nucleus, and the rest of it was just empty space. He did this through an expirement conducted using gold foil, where it fired radioactive particles through the foils and detected them using zinc sulfide. -
Start of World War 1
The Archduke, Franz Ferdinand was assasinated by members of the Black Hand. -
Neils Bohr Atomic Theory!
Neils Bohr's atomic theory is best explained as the 'planetary model' of an atom. It shows the neutrons and protons occupying the nucleus, as the electrons orbit the nucleus as planets orbit the sun. -
Louis de Broglie's Discovery!
In this year, Louis de Broglie discovered the wave Properties of Electron Interactions. He realized that standing waves exist at discrete frequencies, which further proved that energies are also true. In 1929 he was given a Nobel Prize for his discoveries. -
Werner Heisenberg's Discovery
He discovered the fundamental law of nature by hitting an element with gamma rays and noting the change in the electron behavior. This law stated that, the more precisely you measure one property, the more you throw the other off. Basically, the more close you come to one measurement, the further you are away from the other. -
James Chadwick's discovery!
James Chadwick proved the existance of the neutron, a nuetrally charged particle of atom. This supported Ernest Rutherford's previous, less accepted claim. He found this out by testing Beryllium and studying it's radiation, which let out neutrons. -
Erwin Schrodinger's Atomic Theory
This theory stated that electrons behave in a wave-like manner rather than just as particles and that their exact location within an orbit could not be precisely calculated (http://www.green-planet-solar-energy.com/electron-arrangement.html).
