Nuclear Chemistry

1. Nuclear Chemistry

2. 23.1

3. Nuclear Reactions vs. Normal Chemical Changes • Nuclear reactions involve the nucleus • The nucleus opens, and protons and neutrons are rearranged • The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy • “Normal” Chemical Reactions involve electrons, not protons and neutrons

4. I. Nuclear Chemistry A. Wilhem Rontgen - discovered x-rays in 1895 B. Antoine Henri Becquerl - discovered radioactivity 1. photographic plates and rocks C. Marie and Pierre Curie - discovered other radioactiveelements 1. Marie first person to win the Nobel peace prize twice

5. 2. husband run over by wagon when he was crossing the street 3. Marie and her children died of radiation poisoning

6. Radioactivity • One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work ofMarie Curie(1876-1934). • She discoveredradioactivity, the spontaneous disintegration of some elements into smaller pieces.

7. II. Radioactivity A. Spontaneous break down of an unstable nucleus withthe release of particles and rays B. Mass defect and nuclear stability 1. the sum of the particles(protons, neutrons andelectrons) that make up an atom but does not add upto the mass of an atom 2. the difference between the sum of the masses andthe atomic mass is know as the mass defect

8. Mass Defect • Some of the mass can be converted into energy • Shown by a very famous equation! E=mc2 Energy Mass Speed of light

9. C. Nuclear binding energy 1. The energy released when a nucleus is formed from nucleons (protons and neutrons)

10. III Properties of Radioactive elements 1. They affect photographic film 2. They produce electric charges in the surrounding air 3. They produce fluorescence with certain compounds a. fluorescence - makes thing glow

11. 4. Their radiation’s have special physiological effects a. causes mutations in cells - changes in the DNA of cells causing rapid growth and a change in their function 5. They undergo radioactive decay a. Radioactive decay - they emit particles from the nucleus making simpler atoms i. half-life - the time it takes 1/2 a given amount to decay ii. Half-lives can be from a few seconds to millions of years

12. Half-Life • HALF-LIFE is the time that it takes for 1/2 a sample to decompose. • The rate of a nuclear transformation depends only on the “reactant” concentration.

13. Kinetics of Radioactive Decay For each duration (half-life), one half of the substance decomposes. For example: Ra-234 has a half-life of 3.6 daysIf you start with 50 grams of Ra-234 After 3.6 days > 25 grams After 7.2 days > 12.5 grams After 10.8 days > 6.25 grams

14. Half-Life Decay of 20.0 mg of 15O. What remains after 3 half-lives? After 5 half-lives?

15. e.g. The half-life of Plutonium -239 is 24110 years. Of an original mass of 100. g, how much remains after 96440 years first find the number of half-life's # Half-lifes = 96440 years 24110 Years = 4 now divide the gram sample in 1/2 four times 100 ===> 50 ===> 25 ===>12.5 ===> 6.25 4 3 2 1

16. The half-life of thorium -227 is 18.72 days. How many days are required for 3/4 of a given amount to decay 18.72 days 18.72 days 1 ===> 1/2 ===> 1/4 This tells you that you have 1/4 of the original amount left - therefore - 3/4 of a given amount has decayed you must multiply 18.72 days by 2 == 37.44 days

17. e.g Exactly 1/16 of a given amount of protactinium-234 remains after 26.76 hours. What is the half-life of protactinium - 234 First find the number of half-life's 1 ==> 1/2 ===> 1/4 ===> 1/8 ===> 1/16 You must pass threw 4 half life’s 26.76 hours 4 half-life’s = 6.69 hours/half-life

18. The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 78 hours?

19. Nuclear Stability • Certain numbers of neutrons and protons are extra stable • n or p = 2, 8, 20, 50, 82 and 126 • Like extra stable numbers of electrons in noble gases (e- = 2, 10, 18, 36, 54 and 86) • Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons • All isotopes of the elements with atomic numbers higher than 83 are radioactive • All isotopes of Tc and Pm are radioactive 23.2

20. When the number of protons in a stable nuclei is plotted against the number of neutrons Band of Stability and Radioactive Decay

21. 3115P 21H, 63Li, 105B, 147N, 18073Ta 199F Stability of Nuclei • Out of > 300 stable isotopes: N Even Odd Z 157 52 Even Odd 50 5

22. Radioactive decay 1. types of particles a. alpha particles, a, contain two protons and two neutrons - can be stopped by a piece of paper - have low penetrating power - may cause burns to the flesh b. beta particles, b, high speed electrons, travel at close to the speed of light, c, which is equal to 3 x 108 m/sec or 186,000 miles asec c. gamma rays, g, are high energyelectromagnetic waves. Most penetrating

23. Types of Radiation • Alpha – a positively charged (+2) helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons • Beta – an electron • Gamma – pure energy; called a ray rather than a particle

24. Other Nuclear Particles • Neutron • Positron – a positive electron • Proton – usually referred to as hydrogen-1 • Any other elemental isotope

25. Penetrating Ability

26. A X Mass Number Element Symbol Z Atomic Number a particle proton neutron electron positron or or 1H 1p 0b 0e or 1 1 +1 1n 0e +1 0b 0 -1 -1 4a 4He or 2 2 Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons A 1 1 0 0 4 1 0 -1 +1 2 Z 23.1

27. 3. radioactive decay sequence 238U92 ---->a+ 234Th90 daughter parent when you have an alpha ejection - you lose 2 protons and 2 neutron The 92 of uranium is the number of protons andwill go to 90 with an alpha ejection - the numberof protons in you nucleus determines the element.

29. therefore - U turns into Th The 238 of U is the total number of particles in the nucleus = number of protons and neutrons - with an alpha ejection - you lose 2 protons and 2 neutrons your mass goes down by 4 or become234 226Ra88----> a+ 222Rn86

30. When you have a beta ejection - you have a neutron change to a protons thus causing your number of protons to go up by one.The total number of particles in the nucleus doesnot change 234Pa91----> 234U92+ beta particle 234Th90---->234Pa91+ b

32. On page 724 do problems 33,34,35,40,41,42,43

33. or alpha particle - 212Po 4He + AX 2 Z 84 212Po 4He + 208Pb 2 82 84 4a 4He 2 2 212Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212Po. 212 = 4 + A A = 208 84 = 2 + Z Z = 82 23.1

34. 14C 14N + 0b + n 6 7 -1 40K 40Ca + 0b + n 19 20 -1 1n 1p + 0b + n 0 1 -1 11C 11B + 0b + n 6 5 +1 38K 38Ar + 0b + n 19 18 +1 1p 1n + 0b + n 1 0 +1 n and n have A = 0 and Z = 0 Nuclear Stability and Radioactive Decay Beta decay Decrease # of neutrons by 1 Increase # of protons by 1 Positron decay Increase # of neutrons by 1 Decrease # of protons by 1 23.2

35. 37Ar + 0e 37Cl + n 18 17 -1 55Fe + 0e 55Mn + n 26 25 -1 1p + 0e 1n + n 1 0 -1 212Po 4He + 208Pb 2 82 84 252Cf 2125In + 21n 98 49 0 Nuclear Stability and Radioactive Decay Electron capture decay Increase # of neutrons by 1 Decrease # of protons by 1 Alpha decay Decrease # of neutrons by 2 Decrease # of protons by 2 Spontaneous fission 23.2

36. What radioactive isotope is produced in the following bombardment of boron? 10B + 4He ? + 1n 5 2 0

37. What radioactive isotope is produced in the following bombardment of boron? 10B + 4He 13N + 1n 5 2 7 0

38. Write Nuclear Equations! Write the nuclear equation for the beta emitter Co-60. 60Co 0e + 60Ni27 -1 28

39. Positron emission -conversion of a proton to a neutron by the emission of a positron 1. Positron - particle that has the same mass as an electron, but has a positive charge Gamma radiation - does not change the identity of the element but makes the atom more stable Transmutation - changing the identity of an element through the release of radioactive particles Isotopes - atoms of the same element that have different number of neutrons

40. Geiger-Müller Counter 23.7

41. Geiger Counter • Used to detect radioactive substances

42. Artificial Nuclear Reactions New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4He and 11B. Reactions using neutrons are called g reactions because a g ray is usually emitted. Radioisotopes used in medicine are often made by g reactions.

43. Artificial Nuclear Reactions Example of a g reaction is production of radioactive 31P for use in studies of P uptake in the body. 3115P + 10n ---> 3215P + g

44. Transuranium Elements Elements beyond 92 (transuranium) made starting with an g reaction 23892U + 10n ---> 23992U + g 23992U ---> 23993Np + 0-1b 23993Np ---> 23994Pu + 0-1b

45. Biological Effects of Radiation Radiation absorbed dose (rad) 1 rad = 1 x 10-5 J/g of material Roentgen equivalent for man (rem) 1 rem = 1 rad x Q Quality Factor g-ray = 1 b = 1 a = 20 23.8

46. Effects of Radiation

47. Nuclear Fission Fission is the splitting of atoms These are usually very large, so that they are not as stable Fission chain has three general steps: 1. Initiation. Reaction of a single atom starts the chain (e.g., 235U + neutron) 2. Propagation. 236U fission releases neutrons that initiate other fissions 3. Termination.

48. Nuclear Fission

49. 235U + 1n 90Sr + 143Xe + 31n + Energy 0 38 0 54 92 Nuclear Fission Energy = 3.3 x 10-11J per 235U = 2.0 x 1013 J per mole 235U = 235 grams = 0.5 lbs Combustion of 1 ton of coal = 5 x 107 J 23.5

50. Representation of a fission process.