Atom model

Chemistry: History of the Atom (and stuff) by Kelly

  • 100


    Aristotle, born 384 B.C., did not agree with Democritus, because he didn’t believe “nothingness” could exist.
  • 100

    Caesar is Assassinated

    Caesar is Assassinated
    In 44 B.C., Julius Caesar was assassinated by a bunch of Roman senators, including Caesar’s good buddy Brutus. Et tu, Brute?
  • 100

    Birth of Christ

    Birth of Christ
    In the year 1, Jesus was born. He founded Christianity, performed loads of miracles, was crucified, and then rose from the dead. ‘Nuff said.
  • 100


    Democritus, born 460 B.C., was the first person to propose that matter is not infinitely divisible, and believed that matter was made of tiny individual particles called atomos (origin of word “atoms”), and that they that moved around in a “void”. He was also a really optimistic, happy guy.
  • Jan 1, 1254

    Scotland's Rebellion

    Scotland's Rebellion
    In 1254, Scotland rebelled against England’s tyranny, resulting in much bloodshed and much later, the movie Braveheart.
  • Jan 1, 1440

    The Printing Press

    The Printing Press
    In 1440, the printing press was invented, and was probably the most revolutionary invention of its time.
  • Romeo and Juliet Written

    Romeo and Juliet Written
    In 1594, Shakespeare wrote what is widely considered to be his most famous play: Romeo and Juliet.
  • American Independence

    American Independence
    In 1776, The United States of America declared its independence from Great Britain.
  • Antoine Lavoisier

    Antoine Lavoisier
    In 1789, Lavoisier clarified the concept of an element as a simple substance that couldn’t be broken down by any known method of chemical analysis. He also compiled a list of the known elements. At the time, there were only 23.
  • Joseph Proust

    Joseph Proust
    In 1794, Proust published his Law of Definite Proportions (or Law of Constant Composition), which states that a compound is composed of exact proportions of elements by mass, no matter what. The proportion between the different elements that make up a compound are always the same for that compound.
  • John Dalton

    John Dalton
    Dalton revived Democritus’ theory in 1803, the first guy to really do so since the B.C.’s, and his “atomic theory” was very similar to Democritus’. He believed that spherical solid atoms made up matter.
  • Amadeo Avogadro

    Amadeo Avogadro
    In 1811, Avogadro theorized that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. He also said that relative molecular weights of any two gases are similar to the ratio of the densities of the two gases under the constant conditions of temperature and pressure. This is now known as the Avogadro’s principle.
  • Lincoln is Assassinated

    Lincoln is Assassinated
    In 1865, President Abraham Lincoln was assassinated by John Wilkes Booth.
  • William Crookes

    William Crookes
    In 1879, Crookes made important discoveries regarding cathode rays, which were important to the discovery of the electron…and later to the invention of the television.
  • Sherlock Holmes is Published

    Sherlock Holmes is Published
    In 1887, Doyle’s A Study in Scarlet, the first Sherlock Holmes story, was published. The fictional detective is now one of the most well-known fictional characters worldwide, along with Mickey Mouse, Superman, Dracula, and Santa Claus.
  • Toaster was Invented

    Toaster was Invented
    In 1893 in Scotland the first toaster was invented and used. Since then, toasters have become one of the most widely used—and arguably the most awesome—small kitchen appliance ever.
  • Henri Becquerel

    Henri Becquerel
    In 1896, Becquerel discovered radioactivity. While he was studying the effect of x-rays on photographic film, he realized some chemicals spontaneously decompose and give off very penetrating rays.
  • J.J. Thomson

    J.J. Thomson
    In 1897, Thomson did a series of cathode ray experiments, to try to figure out what was behind it. Using a series of ratios, he was able to determine that whatever it was, was lighter than the lightest known atom (hydrogen). He concluded that there must be something smaller than the atom: the electron.
  • Madame Curie

    Madame Curie
    In 1898, 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.
  • Max Planck

    Max Planck
    In 1900, Planck studied the light emitted from heated objects, to try to figure out why matter would “glow” in different wavelengths of light at different temperatures. He discovered that matter can gain or lose energy only in small, specific amounts called quanta. So, a quantum is the minimum amount of energy that can be gained or lost by an atom.
  • Albert Einstein

    Albert Einstein
    In 1905, Einstein proposed that electromagnetic radiation has wave-like and particle-like natures. This means that light can be thought of as a bunch of photon particles. Then Einstein calculated that a photon’s energy depends on its frequency.
  • Robert Millikan

    Robert Millikan
    In 1909, Millikan did something called an “oil drop experiment” to determine the charge of an electron, which was negative. His discovery raised another question: if matter is neutral (you don’t electrocute yourself by picking up a pencil) then how is it an atom’s electrons are negatively charged?
  • Ernest Rutherford

    Ernest Rutherford
    In 1911, Rutherford concluded that an atom is mostly empty space, with electrons bouncing around in it, and that each atom contained a nucleus, which took up most of the mass of the atom and was positively charged. He determined that nucleus contained protons, which is what balanced out the charge of the electrons.
  • Start of WWI

    Start of WWI
    In 1914, Archduke Franz Ferdinand was assassinated, leading to the start of WWI.
  • Henry Moseley

    Henry Moseley
    In 1914, using x-ray tubes, Moseley determined the charges on the nuclei of most atoms, and realized that each had a different specific charge. This means that the number of protons (known as the “atomic number) in an atom identifies it as an atom of a particular element.
  • Niels Bohr

    Niels Bohr
    In 1922, Bohr set out to figure out why matter’s emission spectrum is discontinuous (only made of certain frequencies of light). He said that the hydrogen atom has certain allowed energy states. He figured out that these different states have to do with how far from the nucleus the electrons are orbiting. The image is of Bohr and Einstein, just chillin'.
  • Louis de Broglie

    Louis de Broglie
    In 1924, de Broglie did some thinking about how light waves can sometimes behave like particles, so he wondered if electrons could behave like waves. He wrote an equation that said that all moving particles have wave characteristics.
  • Erwin Schrödinger

    Erwin Schrödinger
    In 1926, Schrödinger furthered the de Broglie’s wave-particle theory. He derived an equation that treated hydrogen atom’s electron like a wave. As it turns out, this equation applied equally to atoms of other elements too. His atomic model is known as the quantum mechanical model of the atom.
  • Werner Heisenberg

    Werner Heisenberg
    In 1927, Heisenberg did research regarding electrons. He eventually concluded that it’s not possible to make any measurement on an object without disturbing the object, so you can’t know both the position and velocity of a particle at the same time. This is now known as the Heisenberg Uncertainly Principle.
  • James Chadwick

    James Chadwick
    In 1932, Chadwick worked with Rutherford, and determined that the nucleus also contained neutrons, whose mass was similar to protons, but unlike protons, neutrons have no charge.
  • This Timeline is Completed

    This Timeline is Completed
    This amazingly epic timeline was completed on January 7th, 2015. Woohoo!