1. Atoms

3. Greek Atomic Model • Democritus (400 BC) • Named the atom • Atom cannot be divided

4. Dalton’s Atomic Theory • 1803 • All elements are composed of atoms (not divisible) • Atoms of same element are the same • Atoms of different elements are different

5. Thomson’s Model • 1897 • Atom has smaller parts, like electrons • Atom made of a positive pudding-like material with negatively charged electrons scattered throughout

6. Rutherford’s Model • 1911 • Positive-charged particles in the nucleus • Negative scattered around edges • Gold foil experiment

7. Rutherford’s Experiment

8. Bohr’s Model • 1913 • Electrons move in definite orbits around the nucleus (like the planets move around the sun) • Energy levels located a certain distance from the nucleus

9. Compare the Thomson to the Rutherford/Bohr

10. Wave Theory • Modern model • Electrons do not travel in definite paths • Think electron cloud

11. Atomic Structure

12. Subatomic Particles • protons = positive charge (+) • electrons = negative charge (-) • neutrons = neutral (0 charge)

13. Subatomic Particles

14. Lithium Atom • How many protons? • How many electrons? • How many neutrons?

15. Atomic Number • identifies the element on the periodic table • equals the # of protons in the nucleus

16. Atomic Mass • sum of the # of protons + # of neutrons in the nucleus • changes with isotopes

17. Isotopes • atoms of the same element • same # of protons • different # of neutrons • different atomic mass • examples = hydrogen, carbon, uranium

18. Isotopes

19. Electron Cloud • electrons move about the nucleus locked in a certain area of the electron cloud • location called energy levels

20. Electron Shells

21. # of electrons in each orbital shell • electrons with low energy are found in the energy level closest to the nucleus