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

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

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

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

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

23. Robert Millikan Found the mass of an electron using charged oil drops
9.11 x g

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

26. 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

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

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

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

33. Neutral Nitrogen Has 7 protons Has 7 electrons Neutrons can vary
ISOTOPE

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

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

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