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200
332 BC-Aristotle
Although the date is approximate, Aristotle concluded in his Metaphysics book that all things are made up of form and matter which can only be changed with growth, decay, or motion. Objects are in turn composed of the five elements he believed existed: fire, water, earth, air, and aether. -
200
492 BC- Democritus
One of the creators of the first basis for the Atomic Theory which stated that all objects are made up of little indestructible and indivisible things called atoms. However, his discovery was often questioned because he could not explain the chemical side of his 'atom' idea -
Period: 200 to
Contributiond to the Atom
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Robert Boyle-January 1627 – December 1691
develop a definition of an element ( any substance that can be broken into 2 or more substances is not an element) and helped with " the death" of the four elements.He helped change the way people think of science. -
Isaac Newton
Proposed a mechanical universe with small solid masses in motion. -
John Dalton
Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
Dmitry Mendeleyev
Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law. -
G.J Stoney
Proposed that electricity was made of discrete negative particles he called electrons -
Henri Becquerel
While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays. -
Joseph Thomson
Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, and thus is credited with the discovery and identification of the electron. Thomson is also credited with finding the first evidence for isotopes of a stable (non-radioactive) element in 1913 as part of his exploration into the composition of canal rays (positive ions) and with the invention of the mass spectrometer. -
July 198 and December 1898-Marie and Pierre Curie
Studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium. -
Frederick Soddy
Observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements, discovered "half-life", made initial calculations on energy released during decay. -
Albert Einstein
E=mc2 -
H.G.J Moseley
Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote"The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass -
Electron cloud of probability-1915, 1920
The electron cloud model is an atom model where electrons are no longer depicted as particles moving around the nucleus in a fixed orbit. Instead, as a quantum mechanically-influenced model, we shouldn’t know exactly where they are, and hence describe their probable location around the nucleus only as an arbitrary -
Ernest Rutherford
Studied radiations emitted from uranium and thorium and named them alpha and beta. And using alpha particles as atomic bullets, probed the atoms in a piece of thin gold foil. He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus. -
Niels Bohr
Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons. -
Erwin Schrodinger
Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom. Unlike the Bohr model, the quantum mechanical model does not define the exact path of an electron, but rather, predicts the odds of the location of the electron. This model can be portrayed as a nucleus surrounded by an electron cloud. Where the cloud is most dense, the probability of finding the electron is great -
James Chadwik
Dicovered the "neutron' -
Enrico Fermi
Conducted the first controlled chain reaction releasing energy from the atoms nucleus. -
Murray Gellman
discovered the quark
