Unit 1: Atomic Structure

AP Chemistry

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Alchemy   A pseudoscience that superceded scientific discoveries.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

Robert Boyle - 1661   Studied Gases 1 st to use the term element in its current context in his book The Skeptical Chemist

George Stahl - 1717   Suggested “phlogiston” flowed from burning material A necessary ingredient of combustible material

Joseph Priestly - 1774  discovered oxygen supports combustion

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.

Amedeo Avogadro - 1811   Developed Avogadro’s Law. Equal volumes of gases have equal number of molecules at constant temperature and pressure. Expanded Dalton’s concept of atomic masses

J.J. Berzelius - 1813  Established the 1 st system of using letters to represent elements.

William Prout - 1815  Proposed that Hydrogen was the fundamental material that all other elements were made from. All atomic masses were multiples of the mass of hydrogen.

Michael Faraday - 1833  Found Faraday’s Constant. 1 mole of e = 96500 coulombs.

Alexandre Béguyer de Chancourtois 1862   1 st periodic arrangement of elements. Divided surface of a cylindrical base into 16 segments because oxygen has a mass of 16.

John Newland - 1863  Developed the law of octaves  Properties of elements repeat every eighth element.

Dimitri Mendeleev - 1869    Classification based on chemical properties. Considered the first periodic table.

Left gaps for missing elements and predicted their properties

William Crookes - 1879  Showed that cathode rays stream from the negative pole

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

William Roentgen - 1895   Discovered x-rays.

Rays were penetrating and of short wavelength

Henri Becquerel - 1896   Discovered radioactivity.

Used uranium salts

Marie Curie - 1897    Student of Becquerel Showed that radioactivity is atomic property Isolated radium and polonium

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 -28 g

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

Henry Moseley - 1913  Calculated atomic number by determining the nuclear charge of an atom.

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

Bohr Model

Hydrogen Spectrum

Gilbert Lewis - 1916   Suggested that noble gases have 8 valence electrons Atoms will gain or lose electrons to achieve 8 outer electrons.

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

Wolfgang Pauli - 1924  Pauli Exclusion Principle – 2 electrons cannot have the same 4 quantum numbers

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

James Chadwick - 1932  Discovered the neutron

Other Contributions   C.D. Anderson – 1932  Discovered the positron Enrico Fermi – 1940  Prepared more than 40 radioactive elements