Atom Assignment Timeline

  • 460


    Democritus was born in 460 BC in Abdera, Thrace. He died in 370 BC at the age of 90.
    Democritus invented the atomic hypothesis. According to him, matter can only be subdivided to a certain point. At that point only atoms remain.
    Democritus discovered that atoms differ from each other only in size and shape. Atoms are constantly moving and often collide with each other. When they collide the could bounce of each other or stick together because of the hooks and barbs on their surfaces.
  • Isaac Newton

    Isaac Newton
    Isaac Newton was born on the 22nd of December 1642 in Woolsthorpe-by-Colsterworth, Lincolnshire, England. He died on the 20th of March 1727 at the age of 84.
    Newton recognized atomism, but questioned the creation as a result of pure chance.
    Newton believed that atoms were held together by attractions known as forces. He adapted atomism to fit his idea of God’s role in creation. His universal law of gravitation opened new theoretical vistas which enhanced the development of atomic theory.
  • Antoine Lavoisier

    Antoine Lavoisier
    Antoine Lavoisier was born on the 26th of August 1743 in Paris, France. He died on the 8th of May 1794 at the age of 50.
    Lavoisier was expected to follow in his father’s footsteps. He even got his license to practice law. After that he turned to geology. He named both hydrogen (H) and oxygen (O) and began new chemical nomentclature. Also, he discovered that matter has the same mass when it changes state and shape.
    Lavoisier is known as the creator of modern chemistry.
  • John Dalton

    John Dalton
    John Dalton was born on the 6th of September 1766 in Eaglesfield, England. He died on the 27th of July 1844 at the age of 77.
    Dalton based his theory on the idea that atoms of different elements could be distinguished by changes in their weights.
    Dalton discovered that there was a point where matter can not be broken down into anything smaller. He called the tiny particles 'atoms'.
    He came up with the atomic theory that all matter is made up of atoms.
  • George Johnstone Stoney

    George Johnstone Stoney
    George Johnstone Stoney was born on the 15th of February 1826 in Oakley Park. He died on the 5th of July 1911 at the age of 85.
    Stoney came up with the idea of electrons.
    He suggested that a subastomic particle existed. A particle of electricity help within the atom, this particle was called the electron. The electron was made up of separate negative particles. This proved to us that inside the atom, there are other particles and that atoms have a charge.
  • William Crookes

    William Crookes
    William Crookes was born on the 17th of June 1832 in London, England. He died on the 4th of April 1919 at the age of 86.
    Crookes applied the new technique to the study of selenium compounds.
    He was noted for his discovery of thallium and for his cathode ray studies.
    Crookes discovered the dark space around the cathode, which is now known as the Crookes dark space. He created multiple devices to study the the behavior of cathode rays, but his theory proved wrong in many ways.
  • Wilhelm Röntgen

    Wilhelm Röntgen
    Wilhelm Röntgen was born on the 27th of March 1845 in Lennep, Rhine Province, Germany. He died on the 10th of February 1923 at the age of 77.
    Röntgen was experimenting with electric current flow and he noticed that a nearby piece of barium platinocyanide gave off light when the tube was in operation. His theory was that when the electrons struck the glass wall of the tube, an unknown radiation was formed and it traveled across the room, struck the chemical and caused the fluorescence.
  • Joseph John Thomson

    Joseph John Thomson
    Joseph Thomson was born December 18 1856 in Manchester, England. He died August 30 1940 at the age of 83.
    Thomson investigated cathode rays.He used the calculated velocity and deflection of the beam to come up with the ratio of electric charge to mass of the cathode ray.The metal of the cathode ray was about 100x less than the value calculated. His theory proved that no matter where matter came from, it held particles that were the same and are smaller than the atoms that matter is formed from.
  • Ernest Rutherford

    Ernest Rutherford
    Ernest Rutherford was born on the 30th of August 1871 in Brightwater, New Zealand. He died on the 19th of October 1937 at the age of 66.
    Rutherford published his atomic theory explaining that the atom has a positive nucleus in the center of negative orbiting electrons. His theory suggested that most of the weight of the atom was in the nucleus and it was mainly surrounded by empty space. This discovery showed that there was something dense and positively charged inside the atom.
  • Francis Aston

    Francis Aston
    Francis Aston was born on the 1st of September 1877 in Harborne, Birmingham. He died on the 20th of November 1945 at the age of 68.
    Aston invented the mass spectrograph. He was also the first person to notice isotopes. He observed that there were three distinctive types of hydrogen atoms. Most of the atoms had a mass number of 1 but he noticed that some hydrogen atoms have a mass number of 2 or 3.
    Francis Aston’s work helped Rutherford predict the existence of the neutron.
  • Albert Einstein

    Albert Einstein
    Albert Einstein was born March 14 1879 in Ulm, Kingdom of Württemberg, German Empire. He died April 18 1955 at the age of 76.
    Einstein’s impact to the atomic theory extended on the earlier work of scientist Max Planck’s quantum. Einstein is famous for the equation E=mc2 which is energy equals mass times the velocity of light squared. He is thought to be one of the fathers of the modern atomic theory because of his works that explained and provided the first evidence of the existence of atoms.
  • Neils Bohr

    Neils Bohr
    Neils Bohr was born October 7 1885 in Copenhagen, Denmark. He died November 18 1962 at the age of 77.
    Bohr assumed that electrons must travel in stationary orbits that are defined by their angular momentum. He discovered that the energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit.
    Bohr’s idea of the atom is that protons and neautrons make the core and electrons circle around the core in fixed orbits.
  • Erwin Rudolf Josef Alexander Schrodinger

    Erwin Rudolf Josef Alexander Schrodinger
    Erwin Schrodinger was born on the 12th of August 1887 in Vienna, Austria-Hungary. He died on the 4th of January 1961 at the age of 73.
    Schrodinger was an Austrian physicist who studied the Bohr atom model. He used mathematical equations to describe the likelihood of finding an electron in a certain position.The model that Schrodinger came up with is known as the “quantum mechanical model”.
    His model doesn’t show the path of an electron, instead it predicts where the electron will be located.
  • James Chadwick

    James Chadwick
    James Chadwick was born on the 20th of October 1891 in Bollington, Cheshire, England. He died on the 24th of July 1974 at the age of 82.
    Before 1932, the model of the atom was only known to contain positively charged protons and negatively charged electrons.
    Chadwick discovered a neutral particle in the atoms nucleus, he called this the neutron.
    Neutrons are elementary particles that devoid of any electrical charge.
  • Robert Andrews Millikan

    Robert Andrews Millikan
    Robert Millikan was born March 22 1868 in Morrison, Illinois, U.S. He died December 19 1953 at the age of 85.
    Thomson discovered the electrons and Millikan determined the charge of these electrons. Millikan conducted a series of experiments aiming to determine the electric charge carried by an electron. He measured the course of charged water droplets in an electrical field. The results proposed that the charge on the droplets is a multiple of the elementary electric charge.