Timeline of Atomic Theory

  • Period: 700 BCE to

    Atomic Theory

  • 600 BCE

    Asharya Kanada

    Asharya Kanada
    Kanada was always pointing out things as he was always aware of new things when he was a kid. Kanada realized that atoms were indestructible particles and this theory came to him when he was walking with food in his hands, he was slowly eating his food throwing away the small particles one by one and he did this until he can no longer break down the food anymore as you would know this when nothing was left in his hands and he can just smell the food on his hands. Matter can't be divided further.
  • 500 BCE

    Alchemists

    Alchemists
    It started off by Egyptians trying different ingredients out so when someone dies, they will stop their body from decaying by trying out these ingredients. When mixing these ingredients, they succeeding in creating real world elements. The four elements they created through this process was fire, water, earth and wind. These four elements are now all present in the periodic table we use today.
  • 462 BCE

    Empodocles

    Empodocles
    He created the theory that everything in existence is made of fire, earth, water, and wind. These four pure substances were said to be indestructible. He also said that wind has weight to it as well as that the speed of light has limits.
  • 400 BCE

    Democritus

    Democritus
    His theory was that everything is composed of atoms. These atoms were small particles that were always moving. In particular, he said that the body of a human is made up of small atoms. These small atoms were pretty much invisible because of how small they were. They could not have been smaller.
  • John Dalton

    John Dalton
    He believed that all matter was made out of atoms that were indestructible/indivisible building blocks. He also stated that chemical reactions were formed from the rearrangement of reacting atoms and that compounds were formed from the combination of these atoms that made up matter.
  • Max Planck

    Max Planck
    he is a german physicist who created the quantum theory. This theory helped us better understand atomic and subatomic processes. He also contributed to many theoretical physics concepts to do with the structure of matter.
  • J.J. Thomson

    J.J. Thomson
    He proposed that atoms have charges such as negative and positive charges and said that an atom is shaped like a sphere. His model was later called the plum pudding or chocolate chip cookie. This was because the plum or the chocalate chips were considered the electrons inside and the pudding and the cookie was considered the positive medium.
  • Hantaro Nagaoka

    Hantaro Nagaoka
    He developed the quasi-planetary model. This mode suggested that the atom is very big that is a positively charged sphere surrounded by many negative charged electrons that were light in weight. These electrons were said to be bound by electrostatic forces which helped stabilize and attract the large atoms by gravitation.
  • Albert Einstein

    Albert Einstein
    Einstein proposed that light energy can be absorbed by packets called quanta, which did contradict the wave theory of light, this was created by Louis de Broglie. Einstein also created the special theory of relativity, this explained how space and time related to moving objects and when an object approaches the speed of light, the mass of object becomes infinite and will not be able to go any faster than light travels.
  • Ernest Rutherford

    Ernest Rutherford
    He is a New Zealand born physicist that said that an atom is a tiny dense positively charged core called the nucleus. He also stated that electrons were separate from the protons as these negatively charged ions would surround around these protons. An example would be how planets revolve around the sun. This model was simply called the Rutherford Model.
  • Neil Bohr

    Neil Bohr
    He proposed a theory that electrons should move around the nucleus but that can only happen if they are in orbitals. When jumping from one orbital to the other with lower energy, light quantum is produced. He determined the path of an electron. Wavelengths have helped produce light and this may have occurred because of his theory.
  • Louis de Broglie

    Louis de Broglie
    The french physicist discovered that all matter has wave properties based on his knowledge of the wave nature of electrons. He found this out when he was working in labs involving x-rays because these labs made him realize that their maybe a combination between the nature of light and even more so how particles relate to wavelengths.
  • Satyendra Nath Bose

    Satyendra Nath Bose
    Bose found a new way to add to Planck's radiation law because Planck believed that one photon of light can look the same as another of the same color. But Bose said that one photon of light will look different than another light of the same color. Due to this, there must be another way on how to count particles.
  • Werner Heisenburg

    Werner Heisenburg
    Heisenberg discovered that an electron's velocity and location can't be known at the same time. He believed that since an electron is very small, when observing it and using any type of light, the particles of the electron will move in a different direction and speed. When this electron is exposed to light, this causes the speed and direction to be different.
  • Wolfgang Pauli

    Wolfgang Pauli
    Pauli expanded on Neil Bohr's theory by saying that there can only be a maximum of 2 electrons. The number of electrons are known as quantum numbers. He also added his principle which was called the Exclusion Principle, this stated that if an electron has a specific number of quantum numbers than no other electron in the atom can have the same number of quantum numbers.
  • Erwin Schrödinger

    Erwin Schrödinger
    Schrödinger who is a Australian physicist extended everyone's knowledge by using mathematical equations to find the likelihood of spotting an electron in a specific position. The electron in his model was very unlikely to be in a dense area which made it the highest probability.
  • James Chadwick

    James Chadwick
    He discovered that neutrons exist and that they are present in the center of an atom, in the nucleus along with the protons. It was also said by Chadwick that these neutrons had a neutral charge (no charge) so did not play a role in the charge of an atom. It did indeed help us calculate what the atomic mass/ weight of an atom is as that calculation is done by adding the number of protons with the number of neutrons.
  • Irene Joliot Curie

    Irene Joliot Curie
    Currie made the discovery that radioactive elements can be produced from stable elements through a natural process. She did this by mixing aluminum foil with alpha particles. The radioactive source was then removed and this caused the aluminum to be radioactive.
  • Lise Meitner

    Lise Meitner
    She discovered that from nuclear fission, you can create large amounts of energy. She made her discovery in Sweden just a few months before she escaped Nazi Germany. She believed that nuclear energy should be used for peace. Element number 109 was named after her to acknowledge her for her theory. This element is called Meitnerium.
  • Richard F.W. Bader

    Richard F.W. Bader
    He realized that it is very important to know what the electron density of an atom is because it directly affects the behavior of the atoms in molecules. His theory also pointed out that there are no atomic orbitals that are present in the molecules. His book Atoms in Molecules: A Quantum Theory further discussed his idea.
  • Rosalind Frankilin

    Rosalind Frankilin
    She was a biophysicist that helped discover the DNA structure. She would never get credit for it because researcher Maurice Wilkins took the DNA data from Rosalind and gave this data to James Watson who was an american chemist and with this data and Watson was able to complete the correct model of DNA structure. Everyone says that Watson is the one that did it but without Rosalind's data he would not have been able to complete this difficult task.
  • Robert J. LeRoy

    Robert J. LeRoy
    LeRoy figured out how molecules and atoms behave and he also looked at in depth how they bond together and in what way. These different ways include intermolecular forces which is between molecules and intramolecular forces, this is the forces that take place within the molecule. LeRoy referred to the way molecules and atoms bond as the sex life of these atoms and molecules.
  • Ronald Gillespie

    Ronald Gillespie
    Gillespie was very interested in studying chemistry behind the bright colored solutions that include elements such as iodine, sulfur, tellurium, selenium. These elements were dissolved in sulfuric acid. He was interested in the shape of molecules so while he became more knowledgeable on this specific topic, he developed the VESPR Theory. This theory can be used to predict the shapes of molecules. Exampel, linear, cubical,this depends on the number of electron pairs on outer shell.