History of Atomic Theory

Timeline created by coolos
  • John Dalton

    John Dalton
    Discovered the theory that matter is composed of atoms of varying weights and combine into simple ratios weight. He was the first man to create a table of relative atomic weights. Dalton Discovered this in 1803,modern physical science is based mainly on Dalton’s atomic theory which says that : Matter is made up of tiny particles, they are indestructible and unchangeable, elements are designated by the mass of their atoms and when elements react their atoms just combine into whole-number-ratios.
  • J.J Tomson

    J.J Tomson
    In 1897 J.J Thomson discovered the negatively charged electron in the cathode ray tube. He was able to identify the existence of electrons in atoms. His discovery meant that atoms aren’t invisible and can be seen. It also suggested that atoms are spherical and have a positive charge. Because he discovered the electron it led onto the proof that in atoms there are protons, electrons and neutrons. He also learnt that the the atom is divisible.
  • Ernest Rutherford

    Ernest Rutherford
    In 1911 Ernest Rutherford came up with the theory that an atom is mostly empty. His theory proved that the atom had a central nucleus, and in this nucleus surrounding it are electrons that are negative and orbit the atom. Rutherford used the terms ‘ alpha’ and ‘beta’ to describe uranium and thorium which emit different types of radiation. He also noticed that radioactive material took the same amount of time for half of it to decay. Which is now known as its ‘half life’ .
  • Marie Sklodowska Curie

    Marie Sklodowska Curie
    1898 Curie studied the radiation of all compounds containing radioactive elements. She discovered that you can measure the strength of the radiation from uranium.The intensity of the radiation is proportional to the amount of uranium/thorium that is in the compound despite what compound it is. Later she discovered, the ability to emit radiation isn’t based on the arrangement of the atoms in the molecule but it’s linked to the inside of the atom. She was able to find out that uranium and thorium
  • Ernest Rutherford

    Ernest Rutherford
  • Henry Moseley

    Henry Moseley
    He was taught by Ernest Rutherford, and developed the application of the X-Ray spectra to further study the atomic study. In 913 Moseley learnt that an elements atomic number is equal to the number of protons inside the nucleus. With this information he was able to reorganise the whole periodic table based on the atomic number not the atomic mass.
  • Francis Aston

    Francis Aston
    In 1920 he invented the spectrograph. It’s a type of positive ray machine which uses magnetic and electrostatic fields which then produce opposite deflections in the same plane to convert molecules into ions, then sort the ions out by their mass-to-charge ratio. He was able to use this device to identify 212 isotopes. He was the first man to observe the isotopes. He discovered that there were 3 different types of hydrogen atoms. He found out there are hydrogen atoms with mass numbers of 2 and 3.
  • Niels Bohr

    Niels Bohr
    In 1922 Niels Bohr based his theory off Ernest Rutherford. He was able to extend Rutherford’s theory and discover more. His theory was that an atom emits electromagnetic radiation only when an electrons changes energy levels. His theory led on to the that emission of light occurs when an electron moves into a lower energy orbit.Bohr contributed a lot to modern day quantum physics. He said that presented the idea that the outer orbit of an atom can hold more electrons than the inner orbit.
  • Erwin Schrödinger

    Erwin Schrödinger
    Schrödinger discovered the equation that can be used to find the probability of the location of an electron, in relation to the nucleus. Because you cannot determine the exact location and velocity of an electron at the same time. this creates a range of the probability of the shape of the orbits in the atom. Schrödinger determined the shape of the electrons orbitals. He basically used a mathematical equation to find out the location and energy levels of the electron.
  • James Chadwick

    James Chadwick
    n 1932 he discovered the neutron. He found out that the neutron helps maintain the atoms nucleus. He confirmed that the atomic number is set by the number of protons.The neutron has the same mass of the proton which is what makes up most of the atom. Using his theory we now know the atom to have a nucleus with positively charged protons and neutrons while the rest of the atom is in space where negatively charged electrons orbit the nucleus on differing energy levels.
  • Murray Gell-Mann

    Murray Gell-Mann
    In 1953 while studying particles Gell-Mann found that some act strangely. He came up with a new quantum property of particles called the “strangeness number”. After further studying he found more general characteristics which allowed him to sort them into eight different families and named this grouping the ‘eightfold way’. He found that this theory could best be explained by a particle that had three hadrons and each holding a fraction of the charge which he called ‘quarks’