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Early Chemical History

Early Chemical History. Early, early chemistry. Chemistry has been around since people have been around Democritus- 400 BC. Next 2000 years. 4 elements Metals to Au Robert Boyle- 1600’s Joseph Priestly- 1700’s. Real chemistry (late 1700’s). Antoine Lavoisier combustion O 2 measurement

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Early Chemical History

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  1. Early Chemical History

  2. Early, early chemistry • Chemistry has been around since people have been around • Democritus- 400 BC

  3. Next 2000 years • 4 elements • Metals to Au • Robert Boyle- 1600’s • Joseph Priestly- 1700’s

  4. Real chemistry (late 1700’s) • Antoine Lavoisier • combustion O2 • measurement • Law of Conserv of Mass

  5. Joseph Proust (early 1800’s) • A given compound always contains exactly the same proportion of elements by weight • Law of definite proportions

  6. John Dalton • Reasoned that not only the same weight per compound, but same number of atoms

  7. Exp with C and O • wt of O with 1 g C • Cmpd 1 1.33 g • Cmpd 2 2.66 g • Cmpd 2 has 2 X’s the O

  8. Law of Multiple Proportions • When 2 elements form a series of compounds, the ratios of the masses of the 2nd element that combine with 1 g of the first element can always be reduced to small, whole #’s

  9. Dalton’s Atomic Theory • 1. Each element is made of tiny particles called atoms.

  10. Dalton’s Atomic Theory • 2. The atoms of a given element are identical; the atoms of different elements are different in some fundamental way.

  11. Dalton’s Atomic Theory • 3. Chemical compounds are formed when atoms combine with each other. A given cmpd always has the same # and types of atoms.

  12. Dalton’s Atomic Theory • 4. Chemical rxns involve the reorganization of the atoms- changes in the way they are bound. The atoms are not changed.

  13. Water... • Formulas are simple • OH • mass ratio 1:8 • H = 1, O = 8 atomic mass

  14. Joseph Gay-Lussac • 1. Measured (under same T and P) volumes of gases that reacted

  15. Amadeo Avogadro • At same T and P, equal volumes of gases contain the same number of particles • DIATOMICS

  16. The Electron • JJ Thomson • studied electrical discharges in vacuum tubes called cathode ray tubes- high voltage produced negative cathode rays

  17. The Electron • Determined that ray was made of negative particles that he called electrons

  18. Model of the atom • If electrons are negative, atoms are neutral, so there must be a positive part of the atom • Plum Pudding Model

  19. Robert Millikan • Found the mass of an electron using charged oil drops • 9.11 x 10-28 g

  20. Radioactivity • Henri Becquerel found that uranium left marks on photographic plates • spontaneous emission of radiation

  21. Ernest Rutherford (early 1900’s) • Shot positive alpha particles at gold foil • If Thompson’s model was correct, the large alpha particles should crash through gold foil

  22. The Nuclear Atom • Some particles bounced back!! • Defined the nuclear atom

  23. Modern Atomic Structure • Tiny nucleus with large cloud of e- • Nucleus contains protons and neutrons

  24. Different Properties • All atoms composed of the same thing • However… different number and arrangement

  25. Neutral Nitrogen • Has 7 protons • Has 7 electrons • Neutrons can vary • ISOTOPE

  26. Notation • Mass # (A) top number • protons + neutrons • Atomic # (Z) bottom # • just protons

  27. Ions • Elements that have gained or lost an electron • changes charge

  28. Ions • CATIONS- elements lose e-’s (become positive) • ANIONS- elements gain e-’s (become negative)

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