2. Atoms and Their Structure

4. Early Greek Theories 400 B.C. - Democritus crushed substances in400 B.C. - Democritus crushed substances in his mortar and pestle his mortar and pestle There eventually came a point where he couldThere eventually came a point where he could not crush the substance anymore (still kept its integrity)not crush the substance anymore (still kept its integrity) This became know as the atom. (could not be divided)This became know as the atom. (could not be divided) Name atomos - indivisible Democritus

5. Democritus’ Model solid indestructible sphere

6. John Dalton n 1800 -Dalton proposed a modern atomic model based on experimentation not on pure reason. All matter is made of atoms. Atoms of an element are identical. Each element has different atoms. Atoms of different elements combine in constant ratios to form compounds. Atoms are rearranged in reactions. His ideas account for the law of conservation of mass (atoms are neither created nor destroyed) and the law of constant composition (elements combine in fixed ratios).

7. ++ Carbon, C Oxygen, O Carbon Monoxide, CO Carbon Monoxide, CO Mass 12.0 Mass 16.0 Mass 12.0 + Mass 16.0

8. ++ == CarbonOxygen Carbon Monoxide, 1:1 == Carbon Dioxide, 1:2 ++ CarbonOxygen 11 12 Law of Constant Composition

9. John Dalton’s Model solid indestructible sphere

10. Parts of Atoms n J. J. Thomson - English physicist. 1897 n Used a piece of equipment called a cathode ray tube.

11. Thomson’s Experiment Voltage Source +- Metal Disks

12. n Passing an electric current makes a beam appear to move from the negative to the positive end Thomson’s Experiment Voltage Source +-

13. Thomson’s Experiment n By adding an electric field he found that the moving pieces were negative + -

14. Thomson’s Model n Found the electron. n Said the atom was like plum pudding. n The atom is a sphere with a positive charge, where negatively charged pieces are embedded

15. Rutherford’s Experiment n Ernest Rutherford English physicist. (1910) n Used Alpha particles - (He atom, positively charged) n Shot them at gold foil which can be made a few atoms thick.

16. Lead block Uranium Gold Foil Flourescent Screen

17. He Expected n The alpha particles to pass through. n Because… n The positive charges were spread out evenly. (atom is neutral)

18. He Expected

19. What he got……

20. + What he got…..

21. Rutherford’s Model n Atom is mostly empty. n Small dense, positive piece at center.

22. Bohr Model n Electrons move in definite orbits around the nucleus, (like planets circle the sun) n These orbits, or energy levels, are located at certain distances from the nucleus. n Energy separates one level from another.

23. Nucleus Electron Orbit Bohr’s Model

25. Modern View / Wave Model n Nucleus- protons and neutrons. n Electron cloud- region where you ‘might’ find an electron.

26. The Wave Model n It is impossible to determine the exact location of an electron. The probable location of an electron is based on how much energy the electron has.

27. The Wave Model