Chapter 4/25

1. Chapter 4/25 Atomic Structure Nuclear Chemistry

2. A Long, Long Time Ago… • Greek Philosophers- 4 elements are Earth, Water, Fire, and Air • Aristotle- first recorded atomic thoughts • Matter is continuous (no atoms) • Democritus (400 B.C.) - first recorded atomic theory • Atoms are smallest part of matter, each type of matter has different atoms

3. Aristotle and Democritus

4. A Long Time Ago… • Antoine Lavoisier (1782) • Used experiments in closed containers to develop the LCM • Joseph Proust (1799) • Analyzed water to develop the Law of Definite Proportions • John Dalton (1803) • Compiled past research to develop the first useful atomic theory

5. Lavoisier and Proust

6. John Dalton • Dalton’s theory had 4 major tenets • All matter is composed of atoms • Atoms are indivisible • Atoms of 1 element are alike, but different from those of other elements • Atoms combine in small, whole number ratios to form compounds

7. A Reminder • Observation, Observation, Observation • Research • Hypothesis • Experiment, Revise hypothesis lots of times • Results match….may become a theory

8. A Little While Ago… • 1897- J.J. Thomson discovers the electron using a cathode ray tube

9. Cathode Ray Tube Experimenthttp://www.aip.org/history/electron/jjappara.htm

10. The Nucleus Exists! • 1911- Ernest Rutherford uses the gold foil experiment to “discover” the nucleus

11. The Gold Foil Experiment

12. Results of Gold Foil Experiment… • http://online.cctt.org/physicslab/content/Phy1/lessonnotes/atomic/atomicmodelsandspectra.asp • http://micro.magnet.fsu.edu/electromag/java/rutherford/ • Over 98% of the particles went straight through • About 2% of the particles went through but were deflected by large angles • About 0.01% of the particles bounced off the gold foil

13. Rutherford’s Conclusion

14. Rutherford's Nuclear Model • 1. The atom contains a tiny dense center called the nucleus • the volume is about 1/10 trillionth the volume of the atom • 2. The nucleus is essentially the entire mass of the atom • 3. The nucleus is positively charged • the amount of positive charge of the nucleus balances the negative charge of the electrons • 4. The electrons move around in the empty space of the atom surrounding the nucleus • Coworker James Chadwick later adds neutrons

15. Atomic Number # of protons Element Symbol Mass Number Protons + Neutrons Understanding Periodic Blocks 19 K 39.0983

16. Can 20.0983 Neutrons Exist??? • No, 39.0983 is an average mass of all natural K atoms • All K atoms MUST have 19 protons • Some have 20 neutrons, some 19, some 21… • Average is 20.0983 neutrons • Individual isotopes are identified by the number of neutrons

17. Identifying Protons, Neutrons, and Electrons • Chlorine-35 (element-mass number) • # of protons = 17 • # electrons = # protons • # neutrons = mass number – protons • 35-17 = 18 • Why no electrons in atomic mass? • Electron has mass 1/1837 of Proton and Neutron

18. Nuclear symbol notation (nuclide symbols) • Example: 2713Al or 27Al • # protons = ______ • # neutrons = ______ • # electrons = ______ • Problems that arise • Charges and Ions: only changes the number of electrons! • Finding mass number: use symbol, # p+ and no, or periodic table IN THAT ORDER!

19. Atomic Mass Units • Carbon-12 • 6 protons • 6 neutrons • 1 amu = 1/12 mass of a C-12 atom

20. Nuclear Stability- too many neutrons or protons causes instability

21. Chemical vs. Nuclear Change • Chemical Change- produces new kinds of matter with new properties • Involves breaking and forming BONDS • Accomplished by rearrangement of ELECTRONS • Nuclear Change- produces a new nucleus that contains less energy • Involves emission or capture of nuclear particles • Accomplished by changing PROTONS and NEUTRONS in nucleus

22. Nuclear Decay • Nuclear Particles • Alpha- rapidly moving He nuclei with a (+) charge • Beta – rapidly moving electrons with a (-) charge • Gamma – rapidly moving electromagnetic radiation with no mass or charge

23. ALPHA (α) BETA (β) GAMMA (γ) Symbol 42He 0-1e 00γ Shielding Easy (skin/clothes) Medium (aluminum foil) Hard (2 cm lead) Energy High Med Low Biological Hazard High Med Low-Med Actual Hazard Low Med High

24. Other Radiation • Ionizing Radiation- has significant energy to change atoms and molecules into ions • Types: alpha, beta, gamma, x-rays • Effects to living organisms: changes in, DNA (cell death/cancer) • Nonionizing radiation- does not have significant energy to ionize atoms or molecules (types: microwaves, visible light, radiowaves)

25. Nuclear Reactions • Transmutation- Changing the nucleus of the atom to create a new element • How is a Nuclear Equation Written? • Parent nuclide- initial nucleus that undergoes changes • Daughter nuclide- nucleus resulting from decay of parent

26. Types of Nuclear Reactions • Alpha Emission- generally occurs if nucleus has too many protons and neutrons • Beta Emission- results from conversion of neutron to proton and occurs if nucleus has too many neutrons • Positron Emission- results from conversion of proton to neutron and occurs if nucleus has too few neutrons • Gamma Emission- often accompanies other decay processes

27. Example: Alpha Decay • 25299Es  ______ + 42He

28. Radioactive Decay Half-lives • Half-life is the time taken for half of the atoms of a radio-active substance to decay.

29. Half-life • Half-lives can range from a millionth of a second to millions of years

31. Radioactive Dating • Uses carbon-14 to tell age of fossils • C-14 is present constantly in atmosphere • 15.3 decays/min in living organism • decays/min decreases by ½ every 5370 years an organism is dead. • Only useful to 60,000 yrs ago

32. Tracers • Radioactive isotopes used to track pathways • Chemistry/biology- pathways of reactions • Industry and environment- path of groundwater, durability of containers • Medicine- diagnose malfunctions

33. Fission- nucleus broken into 2 smaller nuclei Fusion- smaller nuclei join to form a larger, more stable nuclei Nuclear Reactions for Energy

34. Fission- 92235U fuel used in a chain reaction Limited resource critical mass- minimum mass to sustain chain reaction Risk of runaway chain reaction Produces radioactive waste products Disposal concerns Reaction: Fusion- 12H and 13H used as fuel extracted from sea water not a chain reaction No risk of runaway reaction Nonradioactive waste: helium Problem: needs temp of 200 Million K Reaction: Reactants and Products

35. Control rods- absorb neutrons to slow the chain reaction Made of cadmium Inserted or withdrawn to keep temp of reaction steady Moderators- slow neutrons down so they DO hit uranium fuel rods Made of water, beryllium, or graphite Intended to allow neutrons to be absorbed by uranium Nuclear Power- generated by a controlled fission chain reaction

36. Cooling and Shielding • Water- acts as a coolant and transfers heat between reactor and turbines that produce electricity • Steel & concrete- surround core and protect personnel by absorbing radiation

38. Cherynobyl (Soviet Union, 1986) Runaway fission reaction from core meltdown Radiation escaped to atmosphere 31 dead, estimated 15,000 cancer deaths in next 50 years Three Mile Island (Pennsylvania, 1979) partial meltdown contained before widespread damages Nuclear Meltdowns