Chapter 3 Atomic Theory

1. Chapter 3Atomic Theory

2. Early Theories • 4 elements

3. Democritus(460 - 370 BC) • Greek philosopher • Atomos – indivisible particles • Atoms are the smallest particle that retains the chemical identity

4. The Greeks Used Logic • The Greeks also believed in a combination of elements to make new things. • For example: Water and Earth = Mud • Mud might just seem like a nuisance to us, but back then it was a building material. • Fire and Earth made Lava. • If you are curious check out the Little Alchemy app (game) that can be found in Google Apps. It is a fun game.

5. Jabir Ibn Haiyan(700? - 803 AD) • Father of Chemistry • Practiced Alchemy • Discovered metals

6. Antoine Lavoisier(1743 - 1794) • Law of Conservation of Matter

7. Joseph Louis Proust(1754-1826) • Law of Constant Composition

8. John Dalton (1766 - 1844) • Atomic Theory • This was the true start of our modern theory of matter.

10. Dalton’s Theory • Dalton’s ideas were a good start. • However, we need to look at one of his postulates more closely. • He stated that “All atoms of the same atom are identical…” • He didn’t know about isotopes. The neutron wasn’t discovered for another 130 years.

11. Atomic Theory • Elements made of atoms • Atoms are identical of a given type of element • Atoms neither created nor destroyed • Compounds have fixed ratio of atoms

12. Ben Franklin (1706-1790) • Two types of charge positive (+) and negative (-)

13. Michael Faraday(1791-1867) • Atoms are related to electricity

14. J.J. Thomson(1856 - 1940) • Cathode Ray Tube (CRT) stream of electrons • Plum Pudding Model

15. cathode ray tube

17. Thomson’s Model • This lead directly to the idea of electrons and was a major advancement in atomic theory. • Sometimes this theory is called “Raisins in a Plum Pudding.”

18. Robert Millikan(1838-1953) • Determined charge & mass of electron

20. Henri Becquerel(1852 - 1908) • Uranium exposes film

21. Marie (1867-1934) & Pierre Curie (1859-1906) • Discovered radioactivity elements • Radioactive decay

22. Earnest Rutherford(1871 - 1937) • Discovered radioactivity particles • Discovered Nucleus • Solar system model of atom

23. Discovery of particles

24. gold foil experiment

25. Rutherford’s Gold Foil Experiment • There are animations on the website so that you can get a better visual of the experiment. • Rutherford’s experiment was truly a marvel. • It answered a lot of questions and gave a good framework for future investigations. • Remember that it was still a theory – there is a long way to go in understanding an atom.

26. Early Atomic Theory • At this point, this completes our look at the early contributors into Atomic Theory and Structure. • You were given a lot of names, but here are the ones I want you to focus on: • Democritus, Dalton, Thompson, Rutherford • When we get to other topics, we will explore a few more of them in detail such as Becquerel and the Curies.

27. Study Guide Help • To assist you in your preparation, take note that I will not be asking much if anything about the following scientists: • Ben Franklin, Joseph Proust, Michael Faraday • Robert Millikan, Jabir Ibn Haiyan, and Antoine Lavoisier might get a short question or two on a test or quiz.

28. Niels Bohr (1885 – 1962) • Electrons do not orbit like planets • Described shells or energy levels • Quantum theory

29. H.G.J. Moseley (1887 - 1915) • Discovered protons (+) in the nucleus • Rearranged periodic table

30. Sir James Chadwick (1891-1974) • Discovered neutrons (0) in the nucleus

31. Quarks, Quarks, Quarks (1950s – present) • 6 quarks have been discovered that make up protons and neutrons

33. Protons • Make up the nucleus • Charge +1.602 x 10 -19C • Mass = 1.673 x 10 -24g • Charge +1 • Mass = 1 amu

34. Neutrons • Make up the nucleus • Charge 0 • Mass = 1.675 x 10 -24g • Mass = 1 amu

36. Electrons • Occur in electron Clouds • Charge -1.602 x 10 -19C • Mass = 9.109 x 10 -28g • Charge = -1 • Mass = 0 amu

37. Atoms are small but nuclei are smaller • Diameter of a penny has 810 million copper atoms

38. Atomic Number • Number of protons in an atom • Electrically neutral atoms have the same number of electrons as protons • Ions are formed by gaining or losing electrons

39. Isotopes • Same number of Protons but different numbers of neutrons • Mass number is the sum of the protons and the neutrons • Isotopes have the same chemical properties • Violates Dalton’s atomic theory

41. Masses of Atoms • 1 amu = 1/12 mass of a 12C atom • 99% Carbon 12C • 1% Carbon 13C • Average atomic mass of C is 12.01 amu • Mass number is for one atom • Listed as a decimal on the periodic table

43. Nuclear Symbol

45. Nuclear Reactions • Nuclear reactions involve the nucleus of the atom • Radioactivity is the spontaneous emission of radiation from an atom • Nuclear reactions change elements involved

46. Alpha particle Helium nucleus with no electrons Will bounce off of paper and skin +2 charge Alpha Particle

48. Beta particle High energy electron Come from the decay of a neutrons Will penetrate skin Blocked by aluminum and Plexiglass -1 charge Beta Particle

50. Gamma Rays High energy wave No charge No mass Penetrates skin, damages cells and mutates DNA Blocked by lead Gamma Radiation