1. Chapter 4/25 Atomic Structure Nuclear Chemistry

2. A Long, Long Time Ago… Greek Philosophers- 4 elements are Earth, Water, Fire, and Air Greek Philosophers- 4 elements are Earth, Water, Fire, and Air Aristotle- first recorded atomic thoughts Aristotle- first recorded atomic thoughts Matter is continuous (no atoms) Matter is continuous (no atoms) Democritus (400 B.C.) - first recorded atomic theory Democritus (400 B.C.) - first recorded atomic theory Atoms are smallest part of matter, each type of matter has different atoms 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) Antoine Lavoisier (1782) –Used experiments in closed containers to develop the LCM Joseph Proust (1799) Joseph Proust (1799) –Analyzed water to develop the Law of Definite Proportions John Dalton (1803) 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 Dalton’s theory had 4 major tenets 1.All matter is composed of atoms 2.Atoms are indivisible 3.Atoms of 1 element are alike, but different from those of other elements 4.Atoms combine in small, whole number ratios to form compounds

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

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

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

10. The Nucleus Exists! 1911- Ernest Rutherford uses the gold foil experiment to “discover” the nucleus 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/lesso nnotes/atomic/atomicmodelsandspectra.asp http://online.cctt.org/physicslab/content/Phy1/lesso nnotes/atomic/atomicmodelsandspectra.asp http://online.cctt.org/physicslab/content/Phy1/lesso nnotes/atomic/atomicmodelsandspectra.asp http://online.cctt.org/physicslab/content/Phy1/lesso nnotes/atomic/atomicmodelsandspectra.asp http://micro.magnet.fsu.edu/electromag/java/ruthe rford/ http://micro.magnet.fsu.edu/electromag/java/ruthe rford/ http://micro.magnet.fsu.edu/electromag/java/ruthe rford/ http://micro.magnet.fsu.edu/electromag/java/ruthe rford/ Over 98% of the particles went straight through Over 98% of the particles went straight through About 2% of the particles went through but were deflected by large angles About 2% of the particles went through but were deflected by large angles About 0.01% of the particles bounced off the gold foil 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 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 2. The nucleus is essentially the entire mass of the atom 3. The nucleus is positively charged 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 4. The electrons move around in the empty space of the atom surrounding the nucleus Coworker James Chadwick later adds neutrons Coworker James Chadwick later adds neutrons

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

16. Can 20.0983 Neutrons Exist??? No, 39.0983 is an average mass of all natural K atoms 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) Chlorine-35 (element-mass number) # of protons = 17 # of protons = 17 # electrons = # protons # electrons = # protons # neutrons = mass number – protons # neutrons = mass number – protons –35-17 = 18 Why no electrons in atomic mass? Why no electrons in atomic mass? –Electron has mass 1/1837 of Proton and Neutron

18. Nuclear symbol notation (nuclide symbols) Nuclear symbol notation (nuclide symbols) –Example: 27 13 Al or 27 Al –# protons = ______ –# neutrons = ______ –# electrons = ______ Problems that arise Problems that arise –Charges and Ions: only changes the number of electrons! –Finding mass number: use symbol, # p+ and n o, or periodic table IN THAT ORDER!

19. Atomic Mass Units Carbon-12 Carbon-12 –6 protons –6 neutrons 1 amu = 1/12 mass of a C-12 atom 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 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 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 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. HighMedLow Actual Hazard Low-MedMedHigh Biological Hazard LowMedHighEnergy Hard (2 cm lead) Medium (aluminum foil) Easy(skin/clothes)Shielding 00γ00γ00γ00γ 0 -1 e 4 2 He Symbol GAMMA (γ) BETA (β) ALPHA (α)

24. Other Radiation Ionizing Radiation- has significant energy to change atoms and molecules into ions 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) 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 Parent nuclide- initial nucleus that undergoes changes Daughter nuclide- nucleus resulting from decay of parent 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 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 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 Positron Emission- results from conversion of proton to neutron and occurs if nucleus has too few neutrons Gamma Emission- often accompanies other decay processes Gamma Emission- often accompanies other decay processes

27. Example: Alpha Decay 252 99 Es  ______ + 4 2 He 252 99 Es  ______ + 4 2 He

28. Radioactive Decay Half-lives Half-life is the time taken for half of the atoms of a radio-active substance to decay. 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 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 Uses carbon-14 to tell age of fossils C-14 is present constantly in atmosphere C-14 is present constantly in atmosphere 15.3 decays/min in living organism 15.3 decays/min in living organism decays/min decreases by ½ every 5370 years an organism is dead. decays/min decreases by ½ every 5370 years an organism is dead. Only useful to 60,000 yrs ago Only useful to 60,000 yrs ago

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

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

34. Reactants and Products Fission- 92 235 U fuel used in a chain reaction Fission- 92 235 U 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- 1 2 H and 1 3 H used as fuel Fusion- 1 2 H and 1 3 H 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:

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

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

38. Nuclear Meltdowns Cherynobyl (Soviet Union, 1986) 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) Three Mile Island (Pennsylvania, 1979) –partial meltdown –contained before widespread damages