How have the structures and properties of elements changed over time?

Timeline created by SR16
  • 1,858 BCE

    A number of scientists (Jean Baptiste Dumas, Leopold Gmelin, Ernst Lenssen, Max von Pettenkofer, and J.P. Cooke) found that these types of chemical relationships extended beyond the triad.

  • Hennig Brand discovered phosphorous

  • Hennig Brand discovered phosphorous.

  • Isaac Newton proposed a mechanical universe with small solid masses in motion.

  • 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.

  • John Dalton proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass

  • Johann Dobereiner noticed that the atomic weight of strontium fell midway between the weights of calcium and barium, elements possessing similar chemical properties

  • Johann Dobereiner noticed that the atomic weight of strontium fell midway between the weights of calcium and barium, elements possessing similar chemical properties.

  • Johann Dobereiner proposed that nature contained triads of elements the middle element had properties that were an average of the other two members when ordered by the atomic weight (the Law of Triads).

    after discovering the halogen triad composed of chlorine, bromine, and iodine and the alkali metal triad of lithium, sodium, and potassium
  • Between 1829 and 1858 a number of scientists (Jean Baptiste Dumas, Leopold Gmelin, Ernst Lenssen, Max von Pettenkofer, and J.P. Cooke) found that these types of chemical relationships extended beyond the triad.

  • Michael Faraday studied the effect of electricity on solutions, coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis.

  • J. Plucker built one of the first gas discharge tubes ("cathode ray tube").

  • The first periodic table was published

  • John Newlands wrote a paper which classified the 56 established elements into 11 groups based on similar physical properties, noting that many pairs of similar elements existed which differed by some multiple of eight in atomic weight.

  • John Newlands published his version of the periodic table and proposed the Law of Octaves.

    This law stated that any given element will exhibit analogous behavior to the eighth element following it in the table.
  • A total of 63 elements had been discovered

  • James Clerk Maxwell proposed electric and magnetic fields filled the void.

  • Sir William Crookes discovered cathode rays have 5 different properties

    The cathode rays have the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass.
  • E. Goldstein used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron.

  • G.J. Stoney proposed that electricity was made of discrete negative particles he called " electrons ".

  • Wilhelm Roentgen using a CRT he observed that nearby chemicals glowed. Further experiments found very penetrating rays coming from the CRT that were not deflected by a magnetic field. He named them "X-rays".

  • Henri Becquerel while studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays.

  • J.J. Thomson used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram.

  • J.J. Thomson studied "canal rays" and found they were associated with the proton H + .

  • Rutherford studied radiations emitted from uranium and named them alpha and beta.He estimated atom size and concluded mass was concentrated in the nucleus.

  • Marie Sklodowska 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.

  • 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.

  • Max Planck used the idea of quanta (discrete units of energy) to explain hot glowing matter.

  • Nagaoka Postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle.

  • Abegg discovered that inert gases had a stable electron configuration which lead to their chemical inactivity.

  • Albert Einstein Published the famous equation E=mc 2