Unit 1: Atomic StructureAP 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A pseudoscience that superceded scientific discoveries.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 1st 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 1st 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

1st 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 10-28g

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

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 Schrödinger - 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