SCIENCE Q3 Reviewer

• In 1800, John Dalton performed a series of experiments showing that matter consists of lumpy particles called Atoms. (which is believed to be indivisible)
• John Dalton proposed his model of the atom called the "Billard Ball Model" in 1803. He defined an atom to be a ball-like structure, as the concepts of atomic nucleus and electrons were unknown at the time.
• In 1897, Joseph John Thomson (J.J Thomson) discovered the electron using the cathode ray tube experiment.
• In 1904, J.J Thomson proposed the Plum Pudding Model, following the discovery of the electron. It is also similar to the "raisin bread model"
• In 1886, Eugen Goldstein discovered evidence for the existence of the Proton, however Ernest Rutherford who coined the term for the word "Proton" for the positively charged particle in an atom.
• In 1911, Ernest Rutherford and his coworkers at the University of Manchester, England, directed a narrow beam of alpha particles at a very thin sheet of gold foil called the "Gold Foil Experiment."
• In 1911, Rutherford proposed the Nuclear Model, which all the positive charge and nearly all the mass of the atom were concentrated in a very tiny region called the nucleus at the center of the atom.
• In 1913, Niels Bohr proposed the Planetary Model, in which he modified Rutherford's Model by stating that electrons travel around the nucleus of an atom in distinct circular orbits, or shells.
• In 1926, Erwin Schrodinger proposed the Quantum Mechanical Model, since there is no way to know where the electrons are located. The location of the electrons are often referred to as the "electron cloud."
• An electron cloud has Variable densities: a high density where the electron is most likely to be and a low density where the electron is least likely to be.