The Periodic Table

  • Birth of John Dalton

  • Birth of Johann Wolfgang Döbereiner

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    John Dalton presented his atomic theory

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    John Dalton proposed the 'law of multiple proportion'

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    Johann Wolfgang Döbereiner proposed the 'law of triads'

    Dobereiner proposed the 'law of triads' which implied a relationship between the properties and atomic weights of elements. He also discovered the middle of 3 elements in a triad had a relative atomic mass around the average of the relative atomic masses of the other 2 elements, which was important for the arrangement of elements in the periodic table. However, Dobereiner couldn't prove his hypothesis with enough triads, so his findings were regarded as 'interesting curiosities' in his time.
  • Birth of Dmitri Mendeleev

  • Birth of John Newlands

  • Death of John Dalton

  • Death of Johann Wolfgang Döbereiner

  • Birth of Sir JJ Thomson

  • John Newlands proposed 'law of octaves'

    Newlands discovered that every eighth element in the grouping by atomic weight shared a resemblance and suggested an analogy with the intervals of the musical scale.
  • Dmitri Mendeleev

    Mendeleev was awarded the Chair of General Chemistry at the University of Saint Petersburg at age 33
  • Mendeleev proposed his periodic table

    Mendeleev’s periodic table contained 17 columns, with two nearly complete periods of elements, preceded by two partial periods of seven elements each, and followed by three incomplete periods
  • Mendeelev discovered the periodic law

    His newly formulated law was announced before the Russian Chemical Society in March 1869 with the statement “elements arranged according to the value of their atomic weights present a clear periodicity of properties.”
  • Birth of Ernest Rutherford

  • Birth of Niels Bohr

  • Birth of Henry Mosely

  • Birth of James Chadwick

  • Sir JJ Thomson published observation

    Published paper with obeservation that cathode rays were not a form of radiation but a stream of negatively charged particles with mass, which soon came to be known as electrons
  • Sir JJ Thomson measured cathode ray particles

    First quantitative measurements of cathode ray particles (electrons) produced in 1897 by Thomson using modified CRT
    Measurements from this experiment enables him to determine the charge to mass ratio for the electrons
  • Death of John Newlands

  • Death of Dmitri Mendeleev

  • Ernest Rutherford

    Rutherford proposed an improved model for the atom, that consisted of empty space occupied by electrons, negatively charged particles
  • Henry Mosely: findings of the atomic number

    Mosely discovered that each element emits X-rays at a unique frequency, which confirmed physicist Antonius van den Broek hypothesis he published 2 years earlier; that atomic number might actually be equal to the amount of charge in the atom’s nucleus
  • Niels Bohr proposed new model of atom

    Bohr's model proposed that electrons moved about the central nuclear in circular orbits, first proposed by Rutherford, but that only certain orbit radii are allowed. The electron in each orbit had a specific amount of energy with the lowest orbital radii corresponding to the lowest possible energy. Mosely hypothesised light photon would be emitted from an excited atom when one of its electrons fell from higher energy orbit to lower energy one. However, he gave no reason for atomic stability
  • Henry Mosely discovered X-ray spectroscopy

    Mosely also discovered x-ray spectroscopy: a new non-destructive method to find out which elements are present in any sample. It worked by bombarding the sample with high-energy electrons and looking at the frequencies of the resulting X-rays, which are like a fingerprint for any elements present in the sample.
  • Henry Mosely proposed a new periodic table

    Mosely rearranged the elements on the periodic table by their number of protons rather than their atomic weights. He saw gaps in his new periodic table and predicted the existence of four new elements, with 43, 61, 72, and 75 protons, which were discovered by other scientists years later
  • Death of Henry Mosely

  • James Chadwick identified neutrons as a chargless particle

    Experimental data by Geiger and Marsden on alpha particle deflection showed that the number of protons in the nucleus equalled half the atom’s relative mass, meaning there must be some other neutral/chargeless particle present in the nucleus
    In 1932, Chadwick identified neutrons as the chargeless particle.
  • James Chadwick: Awards

    James Chadwick was awarded the Hughes Medal if the Royal Society 1932
  • James Chadwick: Awards

    James Chadwick was awarded the Nobel Prize for Physics in1935
  • Death of Ernest Rutherford

  • Death of Sir JJ Thomson

  • Death of Niels Bohr

  • Death of James Chadwick