Stem Chem Atomic Timeline

By YaBoyDKrise
  • 400 BCE

    Democritus Atomic Model

    Democritus created the first atomic model. It was simply a round sphere with no electrons, protons, or neutrons. It helped scientists understand the generic shape of an atom. Small hard particle
  • 322 BCE

    Aristotle

    Aristotle did not believe in the atomic theory, and instead believed that everything was not atoms, but of four elements. Those elements were fire, water, air, and earth.

  • Antoine Lavoisier

    Antoine Lavoisier studied the burning process. He proposed the law of conservation of mass. Mass cant be created or destroyed.

  • Joseph Proust

    Joseph Proust created a theory that states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created, called the law of constant composition, or definite proportions.

  • John Dalton

    John Dalton was the first person to propose that all matter is made of atoms, and cannot be created or destroyed. All atoms are of a given element are identical. Atoms always combine in whole number ratios. Atoms cannot be divided. atoms are rearranged separated or combined in a chemical reaction.multiple proportions.

  • J.J Thompson

    J.J. Thomson discovered the electron by experimenting with a cathode ray tube. He demonstrated that cathode rays were negatively charged. He was the first to think atoms held electrons.

  • Robert Millikan

    Robert Millikancreated an oil drop experiment, which helped to quantify the charge of an electron, which contributed greatly to our understanding of the structure of the atom and atomic theory.

  • Ernest Rutherford

    Ernest is famous for his gold foil experiment in which he demonstrated that the atom has a tiny and heavy nucleus. He designed an experiment to use the alpha particles emitted by a radioactive element as probes to the world of atomic structure.

  • Niels Bohr

    Niels Bohr created a theory for the hydrogen atom, based on the quantum theory that energy is transferred only in certain well defined quantities. He also stated that when jumping from one orbit to another with lower energy, light is emitted. electron cloud is arranged in energy levels. First 2 electrons second is 8 third is 18 and fourth is 42.

  • James Chadwick

    James Chadwick discovered the neutron by bombarding beryllium atoms with alpha particles, and an unknown radiation was produced, called a neutron.

  • Schrodinger and Heisenberg

    Schrodinger and Heisenberg improved the Bohr model by using mathematical equations to describe the likelihood of finding an electron in a certain position. It was called the quantum mechanical model of the atom, or the electron cloud.