How the Understanding of the Atom has changed over time

By abi.sabapathy23
  • 250 BCE

    How was the Atom Invented?

    Democritus made a discovery that all matter consists of small, indestructible particles called Atoms, in 450 BC. Aristotle thought differently than Democritus; he thought that the world was made up of air, water, fire, and earth, instead of tiny particles. Aristotle also believed that there were four earthly elements that moved in straight lines. These four elements were Earth, Water, Fire, and Air.

  • Oxygen's role in Combustion

    Antoine Lavoisier discovered the role oxygen plays in combustion. He recognized and named oxygen in 1778 and hydrogen in 1783 and opposed against the phlogiston theory. Lavoisier also helped to construct the metric system and wrote the first extensive list of elements.

  • Law of Definite Proportions

    In 1794, Joseph Proust published his Law of Definite Proportions. This law states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created. Proust was the first scientist to believe the fact that chemical compounds are formed from definite proportions.

  • Atomic Theory

    In 1803, John Dalton built upon Democritus’ Atom and proposed that elements consisted of atoms that were identical and also had the same mass and that compounds were atoms from different elements combined together.

  • First model of an Atom

    The first model of an atom was developed by English Physicist, JJ Thomson in 1904. Thomson believed that atoms consisted purely of negatively charged electrons. This model was known as the plum-pudding model. This model attempted to consolidate the known properties of atoms at the time which were: Electrons are negatively-charged particles and Atoms are neutrally charged.

  • The existence of a Positive Nucleus

    This theory was later disproved by Ernest Rutherford using the Gold Foil experiment in 1911. In this experiment, Rutherford shot Alpha Particles at Gold Foil. He noticed that some Alpha Particles went through and some bounced back. Hence, implying the existence of a positive nucleus.

  • Quantum Mechanical model of an Atom

    In 1926, an Austrian physicist named Erwin Schrödinger had created a quantum mechanical model of an atom by combining the equations for the behavior of waves with the de Broglie equation to generate a mathematical model for the distribution of electrons that are located in an atom.

  • The Neutron segment of an Atom

    In 1931, James Chadwick discovered the Neutron segment of an Atomic nucleus, explaining the nuclear fission of uranium 235. This also made it possible to produce elements that were heavier than uranium in the lab. In contrast with the helium nuclei (alpha rays) which are charged, and repelled by the considerable electrical forces in the nuclei of heavy atoms, this new tool need not overcome any electric barrier and can penetrate the nuclei of even the heaviest elements.