NUCLEAR CHEMISTRY Introduction to Nuclear Chemistry Nuclear chemistry is the study of the structure of and the they undergo. Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain Atoms often unchanged, although converted into atoms they may be of another element rearranged Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence May involve protons, electrons neutrons, and electrons Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons Associated with small Associated with energy changes large energy changes Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons Associated with small energy changes Associated with large energy changes Reaction rate influenced by temperature, particle size, concentration, etc. Reaction rate is not influenced by temperature, particle size, concentration, etc. The Discovery of Radioactivity (1895 – 1898): found that invisible rays were emitted when electrons bombarded the surface of certain materials. Becquerel accidently discovered that phosphorescent salts produced spontaneous emissions that darkened photographic plates Antoine Henri Becquierel Radioactive decay Discovered by Antoine Henri Becquerel in 1896 He saw that photographic plates developed bright spots when exposed to uranium metals Radioactive Decay – nucleus decays spontaneously giving off an energetic particle The Discovery of Radioactivity (1895 – 1898): isolated the components ( emitting the rays atoms) – process by which particles give off particles – the penetrating rays and by a radioactive source The Discovery of Radioactivity (1895 – 1898): identified 2 new elements, and on the basis of their radioactivity These findings Dalton’s theory of indivisible atoms. Marie Sklodowska Curie with her daughter, Irene. The Discovery of Radioactivity (1895 – 1898): – atoms of the element with different numbers of – isotopes of atoms with nuclei (too / neutrons) – when unstable nuclei energy by emitting to attain more atomic configurations ( process) Alpha radiation Composition – Alpha particles, same as helium nuclei 4 Symbol – Helium nuclei, 2He, α Charge – 2+ Mass (amu) – 4 Approximate energy – 5 MeV Penetrating power – low (0.05 mm body tissue) Shielding – paper, clothing Beta radiation Composition – Beta particles, same as an electron Symbol – e-, β Charge – 1Mass (amu) – 1/1837 (practically 0) Approximate energy – 0.05 – 1 MeV Penetrating power – moderate (4 mm body tissue) Shielding – metal foil Gamma radiation Composition – High-energy electromagnetic radiation Symbol – γ Charge – 0 Mass (amu) – 0 Approximate energy – 1 MeV Penetrating power – high (penetrates body easily) Shielding – lead, concrete Ionizing power and penetrating power: an analogy. Types of radioactive decay alpha particle emission beta emission positron emission electron capture gamma emission Alpha emission Beta Particle emisson 1 0 n p e 1 1 0 1 Review Type of Radioactive Decay Alpha Beta Gamma Particle Emitted 4 2 He 0 -1e α β γ Change in Change in Mass # Atomic # -4 0 0 -2 +1 0 Chemical Symbols A chemical symbol looks like… 14 6 C To find the number of from the , subtract the Half-Life is the required for of a radioisotope’s nuclei to decay into its products. For any radioisotope, # of ½ lives % Remaining 0 1 2 3 100% 50% 25% 12.5% 4 5 6 6.25% 3.125% 1.5625% Half-Life Half-Life 100 90 80 % Remaining 70 60 50 40 30 20 10 0 0 1 2 3 # of Half-Lives 4 5 6 7 Half-Life For example, suppose you have 10.0 grams of strontium – 90, which has a half life of 29 years. How much will be remaining after x number of # of ½ lives Time (Years) Amount years? Remaining (g) You can use a table: 0 1 2 3 4 0 29 58 87 116 10 5 2.5 1.25 0.625 Half-Life Or an equation! Half-Life Example 1: If gallium – 68 has a half-life of 68.3 minutes, how much of a 160.0 mg sample is left after 1 half life? ________ 2 half lives? __________ 3 half lives? __________ Half-Life Example 2: Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days? ______________ Nuclear Fission of a nucleus - Very heavy nucleus is split into approximately fragments reaction releases several neutrons which more nuclei - If controlled, energy is released (like in ) Reaction control depends on reducing the of the neutrons (increases the reaction rate) and extra neutrons ( creases the reaction rate). Nuclear Fission - 1st controlled nuclear reaction in December 1942. 1st uncontrolled nuclear explosion occurred July 1945. - Examples – atomic bomb, current nuclear power plants © 2003 John Wiley and Sons Publishers Courtesy David Bartruff/Corbis Images Cooling towers of a nuclear power plant. Construction of a tunnel that will be used for burial of radioactive wastes deep within Yucca Mountain, Nevada. Disposal of radioactive wastes by burial in a shallow pit. Nuclear Fusion of a nuclei nuclei combine to form a - Two heavier nucleus - Does not occur under standard conditions ( - Advantages compared to fission - repels ) , - Disadvantages - requires amount of energy to , difficult to - Examples – energy output of stars, hydrogen bomb, future nuclear power plants Applications Medicine Chemotherapy Power pacemakers Diagnostic tracers Agriculture Irradiate food Pesticide Energy Fission Fusion X-ray examination of luggage at a security station. An image of a thyroid gland obtained through the use of radioactive iodine Images of human lungs obtained from a γ-ray scan. A cancer patient receiving radiation therapy.