1. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 The Early History of Chemistry 4 Greeks 400 B.C. - Four fundamental substances – fire, earth, water, a air. - Democritus – uses term “atomos” (atoms) to describe small, indivisible matter. No experiments to support the idea, so it is dropped. 4 Before 16th Century – Alchemy: Attempts (scientific or otherwise) to change cheap metals into gold

2. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 The Early History of Chemistry 4 17th Century –Robert Boyle: First “chemist” to perform quantitative experiments (pressure/volume) –-Incorrectly believed that the alchemist’s view that metals were not true elements and that a way would eventually be found to change one metal into another. 4 18th Century –George Stahl: Phlogiston flows out of a burning material. –Joseph Priestley: Discovers oxygen gas, “dephlogisticated air.”

3. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Law of Conservation of Mass 4 Discovered by Antoine Lavoisier 4 Mass is neither created nor destroyed 4 Combustion involves oxygen, not phlogiston

4. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Other Fundamental Chemical Laws 4 A given compound always contains exactly the same proportion of elements by mass. 4 NaCl – always 39.34% Na and 60.66% Cl (mass) 4 Carbon tetrachloride is always 1 atom carbon per 4 atoms chlorine. Law of Definite Proportion

5. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Other Fundamental Chemical Laws 4 When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers. 4 The ratio of the masses of oxygen in H 2 O and H 2 O 2 will be a small whole number (“2”). Law of Multiple Proportions

6. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Law of Multiple Proportions Mass of oxygen that combines with 1 g of Carbon Compound 1 (CO)1.33 g Compound 2 (CO 2 )2.66 g

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Dalton’s Atomic Theory (1808) ÊEach element is made up of tiny particles called atoms. ËThe atoms of a given element are identical; the atoms of different elements are different in some fundamental way or ways.

8. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Dalton’s Atomic Theory (continued) ÌChemical compounds are formed when atoms combine with each other. A given compound always has the same relative numbers and types of atoms. ÍChemical reactions involve reorganization of the atoms - changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.

9. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Dalton’s Atomic Theory (continued) 5.Atoms cannot be subdivided, created, or destroyed. 6.Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.

10. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Early Experiments to Characterize the Atom H J. J. Thomson - postulated the existence of electrons using cathode ray tubes. H Ernest Rutherford - explained the nuclear atom, containing a dense nucleus with electrons traveling around the nucleus at a large distance.

11. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Figure 2.7: A cathode-ray tube. The fast- moving electrons excite the gas in the tube, causing a glow between the electrodes.

12. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Figure 2.8: Deflection of cathode rays by an applied electric field.

13. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Figure 2.10: A schematic representation of the apparatus Millikan used to determine the charge on the electron.

14. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 The Electron H Tiny, negatively charged particle H Very light compared to the mass of an atom – 1/1837 th the mass of a H atom H Move extremely rapidly within the atom.

15. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Figure 2.9: The plum pudding model of the atom.

16. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Figure 2.12: Rutherford's experiment on  -particle bombardment of metal foil.

17. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Figure 2.13: (a) The expected results of the metal foil experiment if Thomson's model were correct. (b)Actual results.

18. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 The Modern View of Atomic Structure l Electrons electron cloud l Protons : found in the nucleus, they have a positive charge equal in magnitude to the electron’s negative charge. l Neutrons : found in the nucleus, virtually same mass as a proton but no charge. l The nucleus contains: protons and neutrons. :

19. Figure 2.14: A nuclear atom viewed in cross section. Note that this drawing is not to scale.

20. Atom is 99.9999 99..% empty space!!! !!

21. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 The Mass and Charge of the Electron, Proton, and Neutron

22. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 The Mass and Charge of the Electron, Proton, and Neutron ParticleRelative Mass Relative Charge Location Electron0Electron cloud Proton1+1Nucleus Neutron10Nucleus

23. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Atomic Number / Atomic Mass H The atomic number is equal to the number of protons. H The atomic mass is equal to the number of protons + neutrons

24. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 Atomic Number / Atomic Mass H Essentially, all of the mass of the atom is considered to reside in the nucleus. H In a neutral atom, the number of protons equals the number of electrons.

25. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 Isotopes H All atoms of an element have the same number of protons. H The number of protons = the atomic number H Atoms of an element with different numbers of neutrons are called isotopes.

26. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 Isotopes continued… H All isotopes of an element are chemically identical H Isotopes have different masses H Isotopes are identified by their mass number.

27. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 The Chemists’ Shorthand: Atomic Symbols K  Element Symbol 39 19 Mass number  Atomic number 

28. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 28 Figure 2.15: Two isotopes of sodium. Both have eleven protons and eleven electrons, but they differ in the number of neutrons in their nuclei.

29. Isotopes Copyright©2000 by Houghton Mifflin Company. All rights reserved. 29 IsotopeAtomic Number Mass Number # of Protons# of Electrons # of Neutrons U-234 Na- 24 201822 32 S 2-