1. Early Ideas about Matter

2. atom u The smallest piece of the element with all the chemical properties of the element u an old and new idea

3. Greeks u Discontinuists –Democritus u Continuists –Aristotle

4. Discontinuists u Democritus u Believed there was a smallest piece u “atomos” = indivisible

5. Continuists u Continuists thought there was no “smallest piece” u they believed a bar of gold, for example, could be cut into smaller pieces forever

6. Aristotle’s ideas u There are four elements –earth, air, fire, and water u all matter is composed of these four elements in different proportions

7. The Alchemists u Tried to turn lead into gold –put more fire into it –the “medicine stone” would “cure” the Pb u developed many lab techniques and apparatus

8. The Renaissance u A new approach to science u experiment to test if the hypothesis is true u many of Aristotle’s ideas were shown to be wrong

9. Law of Conservation of Mass u Lavoisier> France, 1790’s u Matter (or mass) is u neither created nor u destroyed in an ordinary chemical reaction

10. Law of Definite Proportions u In a given compound, elements are always combined in the same proportion by mass. u Ex: H 2 O is always 11% H, 89% O by mass.

11. Dalton’s Atomic Theory u All matter is composed of atoms –atoms are indestructible –“billiard ball” model u In a chemical reaction, atoms are rearranged –conservation of mass

12. u All atoms of the same element are identical u Atoms of one element are different from the atoms of any other element –elements could be identified and distinguished from each other

13. u Atoms combine to form compounds in small whole number ratios. –Ex: could be XY, X 2 Y, XY 2, etc, but never X 1 1 / 2 Y

14. What came next? u 49 new elements were discovered between 1801 - 1900 u new particles were discovered –alpha, beta, gamma - radiation –particles smaller than atoms

15. u 1897: JJ Thomson discovered electrons –smaller than atoms –negatively charged –problem with Dalton’s model u 1914 Rutherford’s Gold Foil Experiment –nuclear model of atom u http://www.shsu.edu/~chm_tgc/sounds/pushmovies/ http://www.shsu.edu/~chm_tgc/sounds/pushmovies/

16. Modern atom u Nucleus –in geometric center of the atom –very small and dense –nearly all of the atom’s mass –gives the atom its identity –protons (+) and neutrons

17. u Electron cloud –gives the atom its size –mostly empty space –electrons –electrons do not “orbit” like planets; more like bees/beehive

18. Summary of the subatomic particles

19. Summary of the subatomic particles particle where? Mass who?

20. Atomic Number u the number of protons in the nucleus of an atom u gives the atom it’s identity u also, equal to the number of electrons in a neutral atom

21. Mass Number u Equal to the number of protons plus the number of neutrons in the nucleus of an atom u #n o = mass # - atomic #

22. Important note! u The atomic number of an element is on the periodic table, but the mass number is usually not! u The location of the numbers on the periodic table is at the printer’s discretion

23. u The good news: –all atoms of the same element have the same atomic number u The bad news: –not all atoms of the same element have the same mass number u What is different? –The number of neutrons

24. isotopes u Atoms of the same element with different mass numbers –different numbers of neutrons u different versions of the same element u no difference in chemical properties u only fundamental difference is in mass

25. Isotope symbols u The elements symbol, plus... u the mass number is written in the upper left corner u the atomic number is written in the lower left corner

26. Examples of isotope symbols u Compare carbon-12, carbon-13, and carbon-14 u each have the same number of protons, but a different number of neutrons

27. Examples of isotope symbols u 12 C6p + 6n o 6 u 13 C6p + 7n o 6 u 14 C6p + 8n o 6

28. elements u There are ~114 known u There are 92 naturally occuring u All have unique name and symbol –1 letter = capitol –2 letters = cap w/ lower case –ex: B, C, Ca, Na