The Phlogiston Theory

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2 The Phlogiston Theory metal + heat = calx of metal + Ø e.g., zinc = zinc oxide + Ø phlogiston (Ø) is lost calx + charcoal(ø) + heat = metal + (fixed air) phlogiston (Ø) is gained Problem: Georg Ernest Stahl ( ) phlogiston has a negative mass!

3 The Co-Discoverer of Oxygen Trained in the ministry Studies on the nature of air Mercurius calcinatus + heat = Mercury + dephlogisticated air HgO + heat = Hg + O Recognized the role of oxygen in the life cycle Joseph Priestley ( ) Told Lavoisier of his findings Held to the phlogiston theory until his death

4 Lavoisier and Combustion Quantitative methods Mass is conserved Combustion is not a loss of phlogiston but a gain of oxygen. Traité de Chimie Antoine-Laurent Lavoisier ( ) and His Wife (Marie- Anne-Pierrette Paulze, ), 1788 Jacques-Louis David (French, ) Dual names for salts Guillotined 1794

5 Atomic Theory 1. Elements composed of indivisible atoms 2. Elements have defined and different masses 3. Elements combine in simple numerical ratios - Law of Multiple Proportions John Dalton ( ) Hydrogen = 1 Azot = 4.2 Carbone = 4.3 Oxygen = 5.5

6 The Rule of Greatest Simplicity For Water: 1g of H / 8g of O Formula = HO But: 1g of H / 2 x 4g of O Formula = HO 2 Or: 2 x 1g of H / 16g of O Formula = H 2 O

7 "One Christmas was so much like another, in those years around the sea-town corner now and out of all sound except the distant speaking of the voices I sometimes hear a moment before sleep, that I can never remember whether it snowed for six days and six nights when I was twelve or whether it snowed for twelve days and twelve nights when I was six." "A Child's Christmas in Wales" --- Dylan Thomas

8 Electrochemical Theory Chemical analysis Modern symbols of the elements Discovers: Ce, Se, Th, Si, Zr, etc. Defines isomerism Electrochemical Theory (Dualism) Jons Jacob Berzelius ( )

9 Electrochemical Theory (Dualism) Salts Acid Base Non-metal Radical + Oxygen Metal + Oxygen

10 The Beginning of the End for Vitalism Converts ammonium cyanate CH 4 N 2 O (inorganic) into urea Friedrich Wöhler ( ) CH 4 N 2 O (organic) An example of isomers Begins the downfall of Vitalism

11 On the Preparation of Artificial Urea: I cannot, so to say, hold my chemical water and I must tell you that I can make urea without needing to have kidneys, or anyhow, an animal, be it human or dog Wöhler to Berzelius For more from the wry pen of Wöhler.

12 Radical Theory Refined chemical analysis Developed laboratory instruction Trained many of the chemists of the day Justus Liebig ( ) Proponent of Radical Theory along with Dumas

13 The Benzoyl Radical Liebig and Wöhler Benzoyl hydride C 7 H 5 O - H (Oil of bitter almond, Benzaldehyde) Benzoyl hydroxide C 7 H 5 O - OH (Benzoic acid) Benzoyl chloride Benzamide C 7 H 5 O - Cl C 7 H 5 O - NH 2

14 Dumas and Liebig Note on the Present State of Organic Chemistry In mineral chemistry the radicals are simple; in organic Chemistry the radicals are compound; that is all the difference. The laws of combination and of reaction are otherwise the same in these two branches of chemistry. Leicester and Klickstein, A Source Book of Chemistry, Harvard, 1952)

15 Substitution Theory chlorination of acetic acid C 4 H 4 O 2 + Cl 6 = C 4 HCl 3 O 2 + H 3 Cl 3 C = 6, O = 16 C 2 H 4 O 2 + 3Cl 2 = C 2 HCl 3 O 2 + 3HCl J. B. Dumas ( )

16 Type Theory The ammonia type N H H H N C 2 H 5 H H August Wilhelm von Hofmann ( ) N C 2 H 5 C 2 H 5 H N C 2 H 5 C 2 H 5 C 2 H 5

17 The Water Type O C 2 H 5 K +! C 2 H 5 I O C 4 H 9 H + KI butyl alcohol Alexander Williamson ( ) O C 2H 5 K +! C 2 H 5 I O C 2H 5 C 2 H 5 ether + KI An expanded version of the ether story

18 Valence recognizes the ability of N, P, As, and Sb to combine with 3 and 5 other elements Kekule develops the idea of valence with carbon compounds. Edward Franklin ( )

19 Quadravalence of carbon Structure of benzene Lehrbuch der Organischen Chemie Friedrich August Kekule ( ) Acetic Acid

20 Kekule's 19 formulas for acetic acid (C 2 H 4 O 2 ) from his Lehrbuch der Organischen Chemie 1867 (pg. 164 & 165)

21 1858 Acetic Acid ( ) Atoms with lines between them

22 Physicist and Chemist Diagrammatical Structural Formulae of Organic Chemistry Joseph Loschmidt ( ) Acetic Acid

23 1865 Acetic Acid Alexander Crum Brown ( ) Atom connectivity Multiple connections

24 The Arrangement of Atoms in Space Carbon is tetrahedral! Jacobus Henricus van t Hoff ( ) st Nobel Prize in Chemistry

25 Mendeleev s Periodic Table Thomson Discovers the Electron Lewis s Cubic Model of the Atom (Covalence) Gilbert N. Lewis ( ) Lewis Dot Formula

26 1902 Cl Cl Cl Cl O O

27 Failure of the Cubic Model Single bond (Cl 2 ) Edge Double bond (O 2 ) Face Triple bond (N 2 ) Cube within a cube?

28 Quantum Mechanics leads to... Resonance Hybridization Linus Pauling ( ) Molecular Orbital Theory The Nature of the Chemical Bond (1939)

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