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RADIOACTIVITY

RADIOACTIVITY. RADIATION. Radiation are when high energy rays and particles are emitted from radioactive sources Radioactivity is the release of the high energy particles or rays. NUCLEAR SYMBOL. Chemists represent certain elements using standard atomic notation

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RADIOACTIVITY

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  1. RADIOACTIVITY

  2. RADIATION • Radiation are when high energy rays and particles are emitted from radioactive sources • Radioactivity is the release of the high energy particles or rays

  3. NUCLEAR SYMBOL • Chemists represent certain elements using standard atomic notation • The rounded mass number is on the left as a superscript • The atomic number is written on the left as a subscript Atomic mass Example: K 39 19 Atomic Number

  4. 20Ne 10 10 20 14 28 28Si 14 3 7Li 3 7 80Br 35 35 80 12 12C 6 6 15 31P 5 31

  5. Whats the difference? Which one is heavier? Group 1 Group 2 Group 3 What is the same? They are all the same color, but have DIFFERENT masses because there are a DIFFERENT number of blocks!

  6. Lets look at this.... p+ p+ p+ p+ n n n n n n Its HYDROGEN!!! Still hydrogen.... Still hydrogen???? Because hydrogen’s atomic number is 1 = 1 proton = 1 electron These are all hydrogen.... But have different number of protons??

  7. ISOTOPES • Isotopes are elements with different number of neutrons • If they have a different number of neutrons, they have a different atomic mass! • But, they still have the same number of protons and electrons p+ p+ p+ n n n n n n

  8. REPRESENTING ISOTOPES • Nuclear symbols are used to represent isotopes • Mass number = superscript • Atomic number = subscript • Naming isotopes only consists of the “name” – “atomic mass” • Examples: • potassium – 40 • carbon - 14

  9. MASS NUMBER • Mass number is a number that represents the total number of protons and neutrons in an atom • Mass number: • Mass # = atomic # + # of neutrons • Number of neutrons: • # of neutrons = mass # - atomic # • Number of protons: • # of protons = mass # - # of neutrons

  10. Examples of isotopes: 14C 6 14 6 8 Atomic mass!!!!!

  11. Example 2 41K 19 41 Potassium -41 19 22 Atomic mass!!!!!

  12. Example 3 8Li 3 8 Lithium - 8 3 5

  13. CHEMICAL REACTIONS • Chemical reactions occur because atom’s DON’T have a valence shell. • Therefore, they are unstable!!! • So they interact with each other by creating ionic bonds or covalent bonds • But ONLY the electron arrangements (configurations) change, NOT THE PROTONS OR NEUTRONS • ... Nuclear reactions are different...

  14. RADIOACTIVE DECAY • Radioactive decay is the process in which the unstable nucleus (protons and neutrons) become stable by emitting radiation • By emitting radiation, the atom changes into another element.... • Isotopes that are capable of radioactive decay are called radioisotopes

  15. ERNEST RUTHERFORD

  16. REVIEW • NUCLEAR SYMBOL • Atomic mass = • Atomic number = Superscript – up high Subscript – down low

  17. THREE TYPES OF RADIATION • Alpha radiation • Stream of positive alpha particles emitted from the nucleus • Beta Radiation • Stream of negative beta particles emitted from the nucleus • Gamma Radiation • Stream of neutral gamma particles emitted from the nucleus

  18. Another Way to Remember ALPHA BETA PROTON ELECTRON

  19. ALPHA RADIATION • A stream of alpha particles emitted from the nucleus • Alpha particles are massive and positively charged • Because their massive, they are slow moving and don’t penetrate materials as much • Alpha particles are essentially the same as helium atoms Symbol:

  20. ALPHA RADIATION • An alpha particle is emitted in a process called alpha decay • Then the atomic mass will decrease by 4 • The atomic number will decrease by 2 • And a new atom will be formed!

  21. Another Example: 201Hg  80 197Pt + 78 4He 2 4He 2 231Pa  91 227Ac + 89

  22. Complete the following: 204Pb 82 227Ac 89 225Ac 89 196Au 79 211Fr 87

  23. BETA RADIATION • Beta particle is an electron and is negatively charged • They are light weight • Fast moving • Greater penetrating power SYMBOL Atomic Mass Electrical charge

  24. BETA DECAY • First a neutron changes into a proton and an electron p+ n e- • Then the proton remains in the nucleus while the electron shoots out with a lot of energy p+ n e- e- • The emission of this electron, or beta particle is called beta decay

  25. Beta Decay • If a beta particle has been emitted • Then the atomic mass will remain the same • But, the atomic number will increase by 1 • And a new atom is formed!! Example:

  26. Another Example 0e -1 24Na  11 24 Mg + 12 201Hg  80 201Tl + 81 0e -1

  27. Complete the following: 201Au 69 14N 7 52Fe 26 6Li 3 24Mg 12 42K 19

  28. GAMMA RADIATION • Gamma radiation consists of rays of high energy, short-wavelength radiation. • The gamma particle emitted during gamma decay has no mass and no charge • Greatest penetrating power • SYMBOL

  29. Gamma Decay • Gamma decay results from the emission of gamma particles • Energy within the nucleus falls from a higher energy state to a lower energy state • It does not change the atomic number or he atomic mass • LOOK FOR *

  30. 7.2 HALF LIFE

  31. Carbon Dating • All organisms on earth contain carbon • Carbon’s isotopes include: • Carbon-12 • Carbon-14 • When an organism is alive • Carbon -12 = Carbon -14 • When an organism dies, carbon-14 atoms start to decrease or decay • Radiocarbon Dating measures the left over carbon-14 to determine age

  32. Radiocarbon Dating...

  33. Half Life Examples • Today you have 100 bucks. After 3 days of spending... You only have 50 dollars left  • How long did it take you to use up HALF of your money? • 3 days • Today you have 10 g of strontium-90. After 29 years of decay, there is only 5 g left! • How long did it take for HALF of the sample to decay?  THAT IS THE HALF LIFE OF YOUR MONEY!!! 29 YEARS!!!!  THAT IS THE HALF LIFE OF YOUR SAMPLE

  34. HALF- LIFE • Half life is the length of time it takes for HALF of the isotope to decay • We compare the rate of radioactive decay by comparing the half life of different isotopes

  35. Decay curve • When we graph the rate of radioactivity, it produces a decay curve • The decay curve for all isotopes look the same • ONLY DIFFERENCE is the length of time it takes for the sample to decay

  36. CALCULATING HALF LIVES

  37. Two Types of Isotopes • The isotope that DECAYS is called the parent isotope • The product AFTER DECAY is called the daughter isotope Parent Isotope Daughter Isotope

  38. As Parent Isotope decays and decreases • Daughter Isotope increases

  39. Parent Isotope + Daughter Isotope = Total Initial mass A parent isotope has an initial mass of 100 g. Its half life is 5 years. Complete the following table: 100 g 0 years 100 g 0 g 50 g 50 g 100 g 5 years 10 years 25 g 100 g 75g 15 years 12.5 g 87.5 g 100 g 20 years 6.25 g 93.75 g 100g

  40. Parent Isotope + Daughter Isotope = Total Initial mass • If this initial mass of the parent isotope is 400 g and it has a half life of 3 years. Complete the following table:

  41. The Half Life Triangle of Time This line is divide TOTAL TIME ALWAYS NEED AT LEAST 2 OF THESE VARIABLES Number of Half Lives HALF LIFE This line means multiply

  42. Examples • If a sample has a half life of 3 years and it has been decaying for a total of 12 years. What is the number of half lives it has gone through? Number of Half Lives Total Time TOTAL TIME Half Life 12 years 3 years Number of Half Lives HALF LIFE Number of Half Lives 4 years

  43. Examples • If a sample has gone through 5 half lives in a total of 25 years. What is the half life of the sample? Total Time Half Life Number of half lives TOTAL TIME 25 years 5 half lives Number of Half Lives HALF LIFE Number of Half Lives 5 years

  44. If mass is given, draw a half life table! • The initial mass of a sample is 100g. After several half lives, the final mass is 12.5g. How many half lives did the sample go through? 0 100g ÷2 1 50g ÷2 2 25g ÷2 3 12.5g Number of half Life = 3!!!!

  45. Mass Table • How many half lives did a sample go through if the final mass is ¼? See a fraction??? CONVERT TO PERCENTAGE!!!!! • Final mass= • ¼ x 100% • = 25% • Initial Mass= • 100% 0 100% ÷2 1 50% ÷2 2 25% Number of half Life = 2!!!! ÷2

  46. Steps to Calculating Half Life!!! LIST ALL VARIABLES Initial mass # of Half Life Final mass Half Lives Total Time Draw Mass Table Triangle of Time Solve for Number of Half Lives Solve for variable of interest

  47. Example 1: Thallium-208 has a half life of 3 minutes. How long does it take for 120 g to decay to 7.50 g? List Variables: Initial mass: Final Mass: 120g # of half lives Half Life: Total Time: 3 min ???? 7.5g ????? TOTAL TIME 0 120g 0g # of half life? 4!!!!! # of ½ life 1 60g 60g ½ Life 2 30g 90g # of ½ lives Total time = ½ life x 3 15g 105g = 3 min X 4 4 7.5 g 112.5g = 12 minutes!

  48. Example 1: Gold-198 has a half life of 3 days. How much of a 96g sample of gold will be left after 9 days? List Variables: Initial mass: Final Mass: 96g # of half lives Half Life: Total Time: 3 days ???? ???? 9 days TOTAL TIME 0 96g 0g # of half life? 3!!!! 1 48g 48g # of ½ life ½ Life 2 24g 72g Total Time 9 days = # of ½ life = 3 ½ life 3 days 12g 84g = 3!!!!

  49. 7.3 NUCLEAR REACTIONS

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