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  • 340

    The Four Elements - Aristotle (340 B.C.)

    The Four Elements - Aristotle (340 B.C.)
    Aristotle believed that four elements made up all of the materials, not atoms (there are also sources that credited five). These "elements" included: earth, which was dry and cool; fire, which is hot and dry; air, which is hot and wet; and water, which is cool and wet. The fifth element was Aether, which made up all of the stars and planets. Other than Plato, Aristotle was not influenced by scientists. Many say that "this contribution was the delay caused to the emergence of the atomic theory."
  • 340

    The Four Elements Diagram (340 B.C.)

    The Four Elements Diagram (340 B.C.)
  • Period: 384 to 322

    Aristotle's Life Span (384 B.C. - after Democritus)

    Aristotle was born in Stagira, Chalkidice. He was a famous Greek philosopher, writing many famous pieces. His exact birth and death dates are unknown, but there was knowledge about what year he died in. Aristotle past away at the age of 62.
  • 460

    The Shape of an Atom - Democritus (460 B.C. before Aristotle)

    The Shape of an Atom - Democritus (460 B.C. before Aristotle)
    Before Aristotle, Democritus developed atomic theories, saying that atoms were "indestructible", and that there is an infinite number of atoms (all shapes and sizes). He showed the earliest ideas of shapes and the connection of atoms. Democritus worked with Leucippus and Epicurus and reasoned that the strength/"solidness" of an atom also depended on its shape. Water atoms were smooth, salt atoms were rough, etc. "by convention bitter, by convention sweet, but in reality atoms and void".
  • Period: 460 to 370

    Democritus Life Span (460 B.C. - before Aristotle)

    Democritus was born before Aristotle, in Abdera, Thrace. He was a Greek philosopher, working with Leucippus and Epicurus. He passed away at the age of 90.
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    Antoine Lavoisier Life Span

    Lavoisier was a french chemist and made many contributions to chemistry and biology. People note him as the "father of modern chemistry". He was known for the ideas of combustion and stoichiometry. Lavoisier past away at the age of 50.
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    John Dalton Life Span

    John Dalton was an English chemist, born in Eaglesfield, Cumbria, United Kingdom, and passing away at the age of 77. He was one of the first to propose the atomic theory.
  • "The First Breakthrough" - Antoine Lavoisier

    "The First Breakthrough" - Antoine Lavoisier
    Antoine Lavoisier was the first to breakthrough the study of chemical reactions. In 1774, he proved that the total mass of matter is the same at the beginning of a chemical reaction. Proving the law of conservation of matter which stated that matter/atoms are neither destroyed nor created in a chemical reaction. Lavoisier was also known for discovering oxygen's role in combustion and in 1787, he published a work to reform the chemical nomenclature and built an entirely new system.
  • The Atomic Theory - John Dalton

    The Atomic Theory - John Dalton
    In 1802, John Dalton developed the atomic theory of matter. He stated that each type of matter was made of only one type of atom. Dalton also believed that atoms were the smallest, they could not be destroyed, taken apart or created. John Dalton proposed using measures of mass. He calculated atomic weights from percentage compositions of compounds and helped explain the law of partial pressure. Dalton stated that atoms all had different weight and complexion.
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    Antoine Henri Becquerel life Span

    Henri Becquerel was a french scientist, working along with the Marie Curie and Pierre Curie. He received the 1903 Nobel Prize in Physics. Henri past away at the age of 55.
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    J.J. Thomson Life Span

    Sir Joseph John Thomson was an English physicist who worked with cathode rays and negatively charged particles. He was credited for finding the first evidence of isotopes and worked with positive ions. Thomson lived to the age of 83.
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    Max Planck's Life Span

    Max Karl Ernst Ludwig Planck is a German, well known quantum theory physicist. His contributions to this category earned him the Nobel Prize in Physics in 1918. Max lived to the age of 89.
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    Marie and Pierre Curie Life Span

    Marie Skłodowska Cuire was a Polish chemist, born on November 7, 1867 and died on July 4, 1934. Her husband, Pierre Curie (May 15, 1859 - April 19, 1906) was french physicist that worked by her side. Together, along with Antoine Henri Becquerel, they won the 1903 Nobel Prize in Physics.
  • Period: to

    Robert Andrews Millikan Life Span

    Millikan is an american physicist, known for the electronic charge and the photoelectric effect, which lead him to win the Nobel Prize for Physics in 1923. He began a series of experiments, testing the charge of an electron. Millikan helped improve Caltech and make it one of the United State's leading research facility. Robert Andrews Millikan past away at the age of 85.
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    Ernest Rutherford Life Span

    Ernest Rutherford is a New Zealand physicist and is known as the father of nuclear physics. He is considered to be one of the greatest experimentalist and worked with the idea of a radioactive half-life. In 1908, he was awarded the Nobel Prize in Chemistry. Rutherford past away at the age of 66.
  • Period: to

    Niels Bohr Life Span

    Niels Bohr made huge contributions to the atomic structure and quantum theory. He was a Danish physicist and received the 1922 Nobel Prize in Physics. Bohr passed away at the age of 77. In honor of him, scientists named an element after him - bohrium.
  • Period: to

    Erwin Rudolf Josef Alexander Schrödinger Life Span

    Erwin Schrödinger was an Austrian physicist, earing the 1933 Nobel Prize in Physics. He wrote much about quantum theory and developed numerous findings. he was notable known for Schrödinger Cat. (Click here for more details:
    Schrödinger passed away at the age of 73.
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    Henry Moseley Life Span

    Henry Moseley was an English physicist, most notable for his contributions to the atomic number. He was strongly influenced by Ernest Rutherford. Sadly, Moseley lived to only the age of 27.
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    James Chadwick Life Span

    Chadwick was born in Cheshire, England and won the1935 Nobel Prize in Physics for his discovery of the neutron
  • Antoine Henri Becquerel's Experiment

    Antoine Henri Becquerel's Experiment
  • Radioactivity - Antoine Henri Becquerel

    Radioactivity - Antoine Henri Becquerel
    Becquerel discovered the phenomenon, radioactivity, when he "imprinted" uranium on a photographic plate. After some experimentation, he was the first to discover that objects emit an invisible radiation. His idea was later emphasized by Marie Curie and Pierre Curie. There were no other people before him who discovered and examined radioactivity. Becquerel discovered that some chemicals gave off penetrating rays after decomposing, which was the effect of x-rays on photographic film.
  • The Electron - J.J. Thomson

    The Electron - J.J. Thomson
    J.J. Thomson had an interest in atomic structure early on, and he published three major works from 1884 to 1892. After going to America in 1896, Thomson made a major study, discovering the electron with cathode rays. Thomson first showed that cathode rays are negatively charged. Then he looked into positively charged atoms, realizing that the old models weren't the most accurate. Thomson so then refined the old model, stating negative particles and positive particles in the new design.
  • J.J. Thomson Plum Pudding Model

    J.J. Thomson Plum Pudding Model
  • Radioactivity - Marie and Pierre Curie

    Radioactivity - Marie and Pierre Curie
    Together, as husband and wife, Marie and Pierre Curie pioneered the study of radioactivity and led to the discovery of two new elements, radium and polonium in 1898. Marie first proposed that radioactivity was caused by something happening inside the element. Both researched together on uranium and proposed that the element is changing from the inside, going against what most scientists thought during that time. After seeing the same affect from thorium, they knew something new was discovered.
  • Quantum Mechanics - Max Planck

    Quantum Mechanics - Max Planck
    Max Planck was most well known for being the creator of quantum mechanics. In 1899, Planck created maximum light with the least amount of light energy of a light bulb. He was notable of atomic and subatomic processes. Using principle of elementary disorder, Planck developed Wien-Planck law from the entropy of an oscillator. Later, Planck also developed the black-body radiation law. Later, Einstein demonstrated Planck's theory using electromagnetic radiation, supporting Planck's particle ideas.
  • Period: to

    Werner Heisenberg Life Span

    Werner Karl Heisenberg was a German physicist and played an important role in quantum mechanics. In 1925, he wrote and published a major paper. He talked about matrices and the uncertainty principle.
  • Ernest Rutherford's Atomic Model

    Ernest Rutherford's Atomic Model
  • Radioactivity - Ernest Rutherford

    Radioactivity - Ernest Rutherford
    In 1897, Ernest Rutherford started his research on radioactivity. He was the first say "alpha waves" and "beta waves" to describe two different types of radiation. In 1902, Rutherford and a few others produced a "Theory of Atomic Disintegration" to summarize radioactive atoms breaking up. In 1909, he performed one of his well known experiments, noticing how some alpha particles were deflected as they passed through a sheet of thin gold, proving the "nuclear nature" of the particles.
  • The Bohr Model - Niels Bohr

    The Bohr Model - Niels Bohr
    Based on Rutherford's theories, Bohr published his own findings about the atomic model. This model showed electrons orbiting the nucleus in orbital shells. The most outer ring determined the chemical qualities of the element. This model is very simplified and presented in schools often. Bohr also stated that electrons can drop energy levels and emit photons, bringing in the basis of the quantum theory. His model is the principle basis, explaining the periodic table ordering of elements.
  • The Bohr Model Diagram

    The Bohr Model Diagram
  • The Atomic Number - Henry Moseley

    The Atomic Number - Henry Moseley
    In 1912, after experimenting with beta particles, Henry Moseley discovered that high potentials could be found from radium, thus creating the first atomic battery. In 1913, Moseley discovered a mathematical relationship between the wavelengths in X-rays and the atomic number of the metals used as targets, which is known as Moseley's Law. He also showed that there were missing gaps in the periodical table of elements, leading him to predict four new chemical elements, which were later found.
  • Henry Moseley's X-Ray Frequency

    Henry Moseley's X-Ray Frequency
  • The Neutron Discovery Diagram (James Chadwick)

    The Neutron Discovery Diagram (James Chadwick)
  • The Photoelectric Effect - Robert Andrews Milllikan

    The Photoelectric Effect - Robert Andrews Milllikan
    Robert Millikan first discovered the charge of an electron in 1910 and proved that this was a constant for all electrons. From 1912 to 1915, Millikan then verified Einstein's photoelectric equation. During the time range of 1920-1923, he worked with the "hot spark spectroscopy" and extended the ultraviolet spectrum. With his discovery of his law of motion and other cases on "electrical phenomena", led him to many significant studies on cosmic radiation.
  • Quantum Mechanics - Werner Heisenberg

    Quantum Mechanics - Werner Heisenberg
    Werner Heisenberg was most notable for his theory in quantum mechanics, which had been published in 1925 and Heisenberg was awarded a noble prize for it. He believed that the revolving of electrons set up by Niels Bohr, who heavily influenced him, could not be assumed to be existent, and stated his principle of uncertainty. This underlies the idea which states how the placement and momentum of an active particle always contains errors and can't be ignored on such a small scale.
  • Werner Heisenberg's Model

    Werner Heisenberg's Model
  • The Neutron - James Chadwick

    The Neutron - James Chadwick
    Chadwick made the first artificial nuclear transformation in 1919, by bombarding an atom with alpha particles, thus leading him to make multiple nuclei studies. In 1932, Chadwick proved the existence of neutrons. After bombarding Beryllium with alpha particles, he saw what he that was gamma radiation being reflected. But upon research, Chadwick discovered that these particles were neutral, naming them neutrons. In 1941, he wrote the MAUD report, inspiring the US to look into the atomic bomb.
  • Quantum Theory - Erwin Rudolf Josef Alexander Schrödinger

    Quantum Theory - Erwin Rudolf Josef Alexander Schrödinger
    Being developed in the works of Niels Bohr, Albert Einstein, and so on, Schrödinger became very interested in quantum mechanics. Schrödinger took Bohr's model one step further. He created a quantum mechanics model that does not show a definite path for the atom but shows the possibilities of where it could be. The picture shows the nucleus and the electron cloud. When the cloud is dense, then there is a possibility of more electrons, introducing sub-energy levels.