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Nuclear Chemistry

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Published in: Chemistry
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Nuclear Chemistry

Sachin S / Pune

14 years of teaching experience

Qualification: M.Sc (Pune University - 2008), B.Sc (Yashwant College - 2006)

Teaches: Chemistry, AIEEE, BITSAT, CET, IIT JEE Advanced, IIT JEE Mains, AIPMT, Medical Entrance Exams, NEET

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  1. Chapter 18 Nuclear Chemistry—- An Introduction to Chemistry by Prof.Sachin Sabne Contact: 8888483015
  2. Chapter Map of t ato 2.4) of stabili . atomic and mass number Writing equal 1m' S (Section 7.1) net ic and polential ener Stabiliry. and
  3. Nuclides • Nuclide = a particular type of nucleus, characterized by a specific number of protons and neutrons and etherefore a specific atomic number and nucleon number. Nucleon number or mass number = the number of nucleons (protons and neutrons) in the nucleus of a nuclide.
  4. Symbolism Mass number (nucleon number Åtomic number Element symbol
  5. Radioactive Iodine One of the products of the fission reaction of uranium atoms with 92 protons and 143 neutrons is iodine atoms with 53 protons and 78 neutrons. 235 92 131 531 235 U 131 1 U-235 1-131 uranium-235 iodine- 131
  6. Two Forces in Nucleus Electromagnetic force = the force that causes opposite electrical charges to attract each other and like charges to repel each other. Strong force = the attractive force between nucleons (protons and neutrons).
  7. Formation Of Helium • Helium-2 with just two protons nucleus is unstable. 2He2 The shorter the distance between the protons is, the stronger the electromagnetic repulsion between them. When they are close enough to form a helium nucleus, the strong force is not strong enough to overcome the electromagnetic repulsion, so the protons are pushed apart.
  8. Nuclear Stability Neutrons increase the attraction from the strong force without increasing electromagnetic repulsion between nucleons. Combining two neutrons with two protons increases the strong force enough to overcome the electromagnetic repulsion, making a stable helium nucleus. 2 He2+
  9. 220 nd 0 staff icy 2 ( ) 0 18 ( ) 16 ( ) : 140 120 Ban of s bili ne 0 on 60 eu n 0 roto ratl 40 20 0 10 20 30 40 50 60 70 80 90 100 1 10 120 Number of protons
  10. z 220 200 180 160 140 120 100 80 60 40 20 Too many protons Alpha emission (alpha decay) Too many neutrons (neutron rich) Beta emission (beta decay) Too few neutrons Positron emission (positron decay) or electron capture 0 10 20 30 40 50 60 70 80 90 100 110 120 Number of protons
  11. Alpha Emission 238 92 Two protons and two neutrons lost 234 // Ihe protons and neutrons leave as an alpha particle.
  12. Beta Emission 131 53 131 A neutron becomes a proto (w ch ys in the nucleus) and an electron (which is ejected from the atom
  13. Positron Emission 40 19K —5 41%Ar A proton becomes a neutron (which stays in the nucleus) and a positron (which is ejected from the atom). Ene
  14. Electron Capture 125 + 53 125 An electron combines wi a proton to forpya neutron. ElQrc
  15. Gamma Emission 137 55 137 * 56 B a ted State 56 Ba + 'I-photon Beta emission Gamma photon
  16. N u Clear Reactions • Nuclear reactions involve changes in the nucleus, whereas chemical reactions involve the loss, gain, and sharing of electrons. Different isotopes of the same element may undergo very different nuclear reactions, even though an element' s isotopes all share the same chemical characteristics.
  17. N UClear Reactions (2) Unlike chemical reactions, the rates of nuclear reactions are unaffected by temperature„ pressure, and the presence of other atoms to which the radioactive atom may be bonded. • Nuclear reactions, in general, give off much more energy than chemical reactions.
  18. Nuclear Equations Alpha emission mass number atomic number Beta emission mass number 238 238 92 U 92 131 131 53 atomic num 53 Positron emissio masGumber 40 40 atomic number 19 Electron capture mass number atomic number 234 234 90 90 131 54 40 40 18 125 52 -F 238 92 131 53 40 19 125 125 53 53 125 125 52 52
  19. General Equations Alpha emission Beta emission Positron emission Electron capture He e
  20. 100 90 80 70 60 50 -g 40 30 20 10 3.1 50% re 5% remai Half-life = the time it takes for one-half of a sample to disappear aining afte one half-li e 25% re aining aft r two half- ives 2.5% rem ining after three half-I • es 6.250 remainin after ur half-liv s ing after fi e half-lives Half-lives
  21. Radioactive Decay Series 238 234 230 226 222 218 214 210 206 81 82 83 218 84 84 85 226 88 86 87 88 Atomic number 89 30 90 91 238 92
  22. Ionization by Alpha Particles 3. The high-velocity alpha particle continues on and can create many ions. 2. The electron can 1. A positively charge combine with alpha particle attracts another uncharged q electrons enough to atom or molecule drag an electron off of to form an anion . an uncharged atom or molecule to form a cation.
  23. Ionization by Beta Particles 3. The high-velocity beta particle continues on and can create many ions. 2. The electron can 1. A negatively charged combine with beta particle repels another uncharged lectrons enough to atom or molecule push an electron off of to form an anion. an uncharged atom or molecule to form a cation.
  24. Ionization by Gamma Rays 2. The electron released might be moving fast enough to push electrons off other atoms and molecules to form many ions. I-ray 1. When a gamma ray collides with an uncharged atom or c molecule, it excites an lectron to such a high energy level that it is removed completely to form a cation. . The electron released can combine with another uncharged atom or molecule to form an anion.
  25. Radiation on Body As the radioactive emissions ionize atoms and molecules, such as water molecules, they also form highly reactive free radicals, which are particles with unpaired electrons. H 20.+ + e- + H 20 H 30+ + OOH H 20 + + OH These reactive particles react with important substances in the body, leading to immediate damage and delayed problems, such as cancer.
  26. Penetration Radioactive Emissions There is an animation that will provide a review of radioactivity at the following web address. • A portion of this animation describes the relative penetrating ability of alpha particles, beta particles, and gamma photons. https://preparatorychemistry.com/radioactivity_Canvas.html
  27. Uses for Radioactive Nuclides Cancer radiation treatment • Computer imaging techniques Radiocarbon dating • Smoke detectors Food irradiation Radioactive tracers
  28. MRI Imaging Protons act like tiny magnets. When patients are put in the strong magnetic field, the proton magnets in their hydrogen atoms line up either with or against the field (called parallel and anti- parallel). parallel + radio wave photons —+ anti-parallel anti-parallel —+ parallel + emitted energy Emitted energy is detected by scanners placed around the patient' s body.
  29. MRI I maging (2) Soft tissues contain a lot of water (with a lot of hydrogen atoms) and bones do not, so the MRI process is especially useful for creating images of the soft tissues of (the body. • Hydrogen atoms absorb and re-emit radio wave photons in different ways depending on their environment, so the computer analysis of the data yields images of the soft tissues.
  30. PET Scan A solution containing a positron-emitting substance is introduced into the body. The positrons collide with electrons, and the two species annihilate each other, creating two gamma photons that move apart in opposite directions. Positron-electron collision followed by the creation of two gamma-ray photons
  31. PET Scan (2) • The gamma photons are detected and the data analyzed by a computer to yield images. Different nuclides are used to study different parts of the body. — Fluorine-18 for bones — Glucose with carbon-Il for the brain
  32. Dating [J not or radiocarbon dating,] we wouCdstiCC be Coun eying in a sea o imprecisions sometimes bred of inspired guesswor but more often of imaginative speculations. Desmond Clark, Anthropologist • Dating to about 50,000 years Natural carbon is 98.89% carbon-12, 1.11% carbon-13, and 0.00000000010% carbon- 14, which come from 14 14
  33. Dating (2) Carbon-14 is oxidized to C02, which is then converted into substances In plants, which are then eaten by animals. Carbon-14 is a beta emitter with a half-life of 5730 years (±40 years), so as soon as it becomes part of a plant or animal, it begins to disappear. 14 14 6C 7N + _le
  34. Dating (3) When alive, intake of 14C balances the decay, so ratio of 14C to 12C remains constant at about in 1,000,000,000,000. When the plant or animal dies, it stops taking in fresh carbon, but the 14C it contains continues to decay. Thus the ratio of 14C to 12C drops steadily. The 14C/12C ratio in the sample is used to calculate its age.
  35. Radiocarbon Dating (4) Assuming that the 14C/12C ratio has been constant over time, if the 14C/12C ratio in a sample is one-half of the ratio found in the air today, the object would be about 5730 years old, A 14C/12C ratio of one-fourth of the ratio found in the air today would date it as 11 ,460 years old (2 half-lives), etc. • It' s not that simple...the percentage of 14C in the air varies due to factors such as volcanoes and natural variations in cosmic radiation.
  36. Dating (5) Tree rings show that the 14C/12C ratio has varied by about ±5% over the last 1500 years. Very old trees, such as the bristlecone pines in California, yield calibration curves for radiocarbon dating to about 10,000 years. These calibration curves are now used to get more precise dates for objects.
  37. Nuclear Stability and Binding Energy Binding energy = the amount of energy released when a nucleus is formed. When two protons and two neutrons combine to form a helium nucleus, energy is released.Ähis is the total binding energy for the helium nucleus. + n 4 11 p
  38. Nuclear Energy The binding energy per nucleon, which is the total binding energy divided by the number of nucleons (protons and neutrons), is a good indication of nuclear stability. • For example, because a uranium-235 atom has many more nucleons than an iron-56 atom, it has a much larger total binding energy, but an iron-56 atom is significantly more stable than a uranium-235 atom. This is reflected in the higher binding energy per nucleon for iron-56. Binding energy per nucleon generally increases from small atoms to atoms with a mass number around 56. Binding energy per nucleon generally decreases from atoms with a mass number around 56 to larger atoms.
  39. 10 20 IONe 16 2He Moreo Stable (Fusion) 56 26 Fe 36 144 138 56 More Stable (Fission) 39 94 Pu o 20 40 60 in ing n rg erN cl o 80 100 120 140 160 180 200 220 240 260 Mass number (A)
  40. Nuclear Energy Because binding energy per nucleon generally increases from small atoms to atoms with a mass number around 56, fusing small atoms to form larger atoms (nuclear fusion) releases energy. Because binding energy per nucleon generally decreases from atoms with a mass number around 56 to larger atoms, splitting large atoms to form medium-sized atoms (nuclear fission) also releases energy.
  41. Nuclear Fusion Deuterium + Tritium Helium + Neutron Products are much more stable than reactants, so products have much lower PE, and a lot of energy is released.
  42. Nuclear Fusion 2 Deuterium + Tritium 2He + on elium + Neutron Requires a very high temperature (about 106 oc) to initiate the fusion. electromagnetic repulsion between the positive nuclei is felt at a relatively long range. — The strong force attraction is only significant when the nuclei are very close. — Therefore, unless the nuclei are rushing together at a very high velocity (very high temperature), the +1+ repulsion slows the nuclei down, stops them, and accelerates them away from each other before they are close enough for the strong force to play a role.
  43. Nuclear Powers the Sun-*—.-— O O
  44. Nuclear Fission rgy 235 92 236 92 56 a 95 36 Kr
  45. Chain Reaction 235 92 products 233 235 92 fission products 235 235 92 fission products
  46. Control rods Pressure Core Nuclear Power Plant ntainment structure Steam line Steam Steam Pump Pump Steam turbine Liquid water Electric generator Cooling water Pressurized Water Reactor (PWR)
  47. Nuclear Power Plant tainment structure Control Pressure vessel Liquid ware r Steam Steam line Pump Steam turbine Liquid water Electric generator Cooling water Boiling Water Reactor (BWR)
  48. Nuclear Plant (2) To get a sustained chain reaction, the percentage of 235U must be increased to about 3%, in part because the unfissionable 238U absorbs too many neutrons. 238 239 921.1 + on 921.1 239 239 92U 93Np + _le 239 239 93Np 94 Pu + —1 e
  49. UF6 enriched in U-235 (sent to next centrafuge) UF6 depleted in U-235 Gas UF6 added More 238UF6 outside More 235UF6 in center UF6 depleted in U-235 More 238 U outside More 235UF6 in center Heater Centrifuge Rotating
  50. Nuclear Plant (3) • Fuel rods — A typical 1000-megawatt power plant will have from 90,000 to 100,000 kg of enriched fuel packed in 100 to 200 S' zirconium rods about 4 meters long. Moderator slows neutrons — 2351J atoms are more likely to absorb slow neutrons. — Can be water
  51. Plant (4) • Control Rods — Substances, such as cadmium or boron, absorb neutrons. c — Control rate of chain reaction — Dropped at first sign of trouble to stop fission reaction

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