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Nuclear Chemistry

Nuclear Chemistry. Remember the easy stuff!!. nucleus. Electrons. We don’t care about the electrons right now…. What particles make up the nucleus?. Both protons and neutrons are called NUCLEONS. protons. neutrons. 238 U. 92. Recall some stuff about the nucleus:. Mass number.

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Nuclear Chemistry

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  1. Nuclear Chemistry

  2. Remember the easy stuff!! nucleus Electrons We don’t care about the electrons right now…

  3. What particles make up the nucleus? Both protons and neutrons are called NUCLEONS protons neutrons

  4. 238U 92 Recall some stuff about the nucleus: Mass number Notation: element Atomic number Isotopes: nuclei with the same number of protons, but not necessarily the same number of neutrons

  5. Isotopes • Isotopes have the same number of protons, different number of neutrons • Another way to show an isotope is to have the mass number follow the name of the element (Carbon-14)

  6. 12C and 13C differ in their (a) number of neutrons. (b) number of protons. (c) number of electrons in orbit around the nucleus. (d) chemical behavior. (e) all of the above.

  7. What is the charge on a proton? The neutron? What is the nature of the force between the nucleons? How does the nucleus hold itself together??!!

  8. The Nucleus is a delicate balance between [1] The attractive nuclear strong force between all of the nucleons, and [2] The repulsive electromagnetic force between all of the protons

  9. It turns out that our delicate balance of forces tends to break down when nuclei get large: The electromagnetic forces eventually overcome the nuclear ones and the nucleus spontaneously breaks apart

  10. This “instability” is called radioactivity: All nuclei having atomic number larger than 83 (bismuth) are radioactive.

  11. Radioactivity • Radioactivity is the process in which an unstable atomic nucleus emits charged particles and energy • Any atom containing an unstable nucleus is called a radioactive isotope or radioisotope for short

  12. As more protons are added (the nucleus gets heavier) the proton-proton repulsion gets larger. • The heavier the nucleus, the more neutrons are required for stability. • The belt of stability deviates from a 1:1 neutron to proton ratio for high atomic mass.

  13. Ratio of neutrons to protons in nucleus determines if nuclei are stable Too many neutrons Too few neutrons nuclei with >than 83 protons all unstable

  14. Radioactive decay is how nuclei get to belt of stability

  15. sometimes an unstable nucleus goes through a series of nuclear reactions before it gains stability. This sequence is called a radioactive series

  16. 3 Types of Spontaneous Decay: 1. Alpha particle emission 2. Beta particle emission 3. Gamma ray emission High energy photon (light)

  17. A little bit of History

  18. Florescent Screen Lead block Uranium Gold Foil Remember this?

  19. This led to the discovery of the nucleus…

  20. Ernest Rutherford’s Other Experiment:

  21. No study on radiation is complete without giving credit to the Curies (Marie, Pierre and Irene)- • Their discoveries include radium, polonium and positron. • Marie-died from Overexposure To radiation

  22. Types of Nuclear Radiation • Alpha 2.Beta 3. Gamma

  23. alpha particles and alpha decay

  24. 4He 2 What is an alpha-particle? It has two protons and two neutrons

  25. 4He 2 What is alpha-decay? It is when a nucleus emits an alpha particle Alpha Decay = Alpha Particle Emission

  26. 1) mass # 2)atomic # Nuclear Equations -represent nuclear decay to become stable - they must balance. The total number of p+and n0 before a nuclear reaction must be the same as the total number of nucleons after reaction.

  27. 1. Alpha emission Nuclides that undergo alpha decay have too many protons for stability ( >83 protons and mass > 209 )

  28. Remember: This is themass number, whichis the number ofprotons plus neutrons Alpha Particles (a)- They have a mass of 4 and charge of +2 Radium Ra226 88 Radon Rn222 86 p + n n p a (4He) 88 protons 138 neutrons 86 protons 136 neutrons 2 protons 2 neutrons • The alpha-particle(a) is a Helium nucleus. • It’s the same as the element Helium, with the electrons stripped off ! • The alpha particles go in the air collide with air molecules and become Helium – not dangerous.

  29. 238U 234X 4He 92 90 2 Example: Write the nuclear equation for the alpha decay of uranium 238: + Now look at the chart to find this one: THORIUM

  30. Nuclear Equation Practice: Alpha Decay How would alpha decay equations be written for these atoms: • 23892 U  • 20984 Po 

  31. beta particles and beta decay

  32. 14C 14N 6 7 Beta Decay Electron! + electron (beta)

  33. 200link 2.Beta emission A neutron turns into a proton and an electron. The beta particle is the electron, written as 0-1 e or0-1

  34. Beta Particles (b)- are electrons, “no” mass and charge of –1. The decay of Carbon 14 Carbon C14 6 Nitrogen N14 7 e- + 0Electron -1 (beta-particle) 7 protons 7 neutrons 6 protons 8 neutrons We see that one of the neutrons from the C14 nucleus “converted” into a proton, and an electron was ejected. The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus. In symbolic notation, the following process occurred: n  p + e

  35. Write out the nuclear equations in each case and identify the daughter nuclei: Alpha decay of 222Rn: Beta decay of 3H: Beta decay of 90Sr 86 1 38

  36. Beta Decay • A beta particle is an electron emitted by an unstable nucleus • Beta particles can be stopped by a thin sheet of metal such as aluminum

  37. Nuclear Reaction Equation Practice: Beta Decay • A beta particle is written 0-1 e or 0-1 • During beta decay, the mass remains the same and the atomic number increases by one • 21482 Pb  • 21884 Po 

  38. 3890Sr is a radioactive isotope that decays by beta-decay. Its daughter nucleus is (a) 3686Kr. (b) 3788Rb. (c) 3789Rb. (d) 3989Y. (e) 3990Y.

  39. gamma rays and gamma decay

  40. Gamma decay occurs because the nucleus is at too high an energy. The nucleus falls down to a lower energy state and, in the process, emits a high energy photon known as a gamma particle. Here's a diagram of gamma decay with helium-3: Gamma decay is only energy emission, not particle emission.

  41. Gamma particles (g) In much the same way that electrons in atoms can be in an excited state, so can a nucleus. Neon Ne20 Neon Ne20 + 10 protons 10 neutrons(in excited state) 10 protons 10 neutrons(lowest energy state) gamma A gamma is a high energy light particle. It is NOT visible by your naked eye because it is not in the visible part of the EM spectrum. It has neither Charge nor mass. They are highly penetrating.

  42. Gamma decay • A gamma ray is a penetrating ray of energy emitted by an unstable nucleus • Gamma rays are energy waves that travel through space at the speed of light

  43. Gamma decay • During gamma decay, the atomic number and mass remain the same, but the energy of the nucleus decreases • Gamma rays can be stopped by several centimeters of lead or by several meters of concrete

  44. Other Types There are other types of radioactive decay we will not go into: - positron emission - neutron emission

  45. Measuring Radiation

  46. The unit of radiation exposure is called the REM (Radiation Equivalent in Man) This is a direct measure of the number of damaged cells. The average dose for one year is about 0.3 Rem Sudden dose of 1000 rems causes death in 30 days!!

  47. Exposure to ionizing radiation: All of these are IONIZING RADIATION alpha beta gamma Ionizing radiation causes cell damage that can lead to DNA damage that can lead to CANCER.

  48. Radiation Doses • Normal • 1 XRay (medical) 0.04 rem = 40 mrem • CAT Scan 3 rem • Portland  New York 1 mrem (4 hr flight) (0.001 rem) • Cosmic Rays 30 – 50 mrem/year • Food (40K, Ra) ~40 mrem/year

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