Unit 1: Atomic Structure Honors Physical Science Evolution of Atomic Theory

Democritus – 400 B.C. Greek Philosopher Imagined particles that were indivisible Constituents of matter Atom comes from “atomos” Opposed Aristotle

Aristotle – 350 B.C. Widely accepted theory that all matter can be continually divided. Set science back for thousands of years.

Alchemy A pseudoscience that superceded scientific discoveries. Alchemists attempted to turn metals into gold and developing the “elixir” of life (able to cause immortality and create life).

Pierre Gassendi - 1650 Reintroduced Particulate theory No experimental evidence Supported by Sir Isaac Newton

Antoine Lavoisier - 1778 Developed Law of Conservation of Mass Explained combustion

Joseph Proust - 1799 Developed “Proust’s Law” using copper oxide Later renamed, the Law of Definite Proportions Nearly discovered the Law of multiple proportions, but his data used percentages instead of weights.

John Dalton - 1802 First to develop an atomic theory. It has 4 postulates. Each element is made up of atoms Atoms of the same element are identical in mass and properties. Atoms of different elements differ in some way.

John Dalton - 1802 Compounds are made when atoms combine. If elements combine in more than one whole number ratio, the resulting compound has different properties Chemical reactions involve the reorganization of atoms.

Eugene Goldstein - 1886 Discovered the proton using a cathode ray tube.

J.J. Thomson - 1897 Determined the mass/charge ratio of the electron. 5.69 x 10-9 Used the cathode ray tube Proposed a model of the atom that was mockingly called the “plum pudding” model

Robert Millikan - 1909 Determined the charge of the electron using the famous oil-drop experiment 1.60 x 10-19 From this and Thomson’s value, the mass was calculated to be 9.11 x 10-28g

Ernest Rutherford - 1911 Performed the famous gold foil experiment Determined 3 things The atom is mostly empty space The nucleus is positively charged The nucleus is a small dense part of the atom

Gold Foil Experiment

Gold Foil Experiment

Niels Bohr - 1913 Observed spectral lines for hydrogen Proposed an orbit theory of the electron around the atom.

Bohr Model

Hydrogen Spectrum

Louis De broglie - 1924 Suggested that matter could exhibit wave properties Observed diffraction patterns in electrons

Erwin Schrödinger - 1926 Developed a wave equation. Mathematical function that described the nature of the electron

James Chadwick - 1932 Discovered the neutron