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Nuclear Chemistry Section 1: Basic Definitions • Nuclear Chemistry – The study of the atomic nucleus, its reactions and radioactivity • Radioactivity – Spontaneous emission of particles and/or energy during nuclear decay Section 1, continued • Nuclear Decay – Spontaneous disintegration of a nucleus – Results in a new element being formed – Occurs when particles and/or energy escape from an unstable nucleus – Releases large amounts of energy • Radiation – Can refer to either the particles or energy released during nuclear decay Section 2: Types of Radiation to Know Radiation Description Radiation Symbol • Proton 1 • Proton: H 1 – Positively charged particle in the nucleus of the atom – Hydrogen nucleus – Most cosmic rays are protons traveling at the speed of light • Neutron 1 • Neutron: n 0 – Neutral particle in the nucleus of the atom • Electron (Beta-minus particle) – Negatively charged particle that moves randomly in specific orbitals outside the nucleus of an atom • Electron: 0 e, β−1 Section 2, continued Radiation Description • Positron (Beta-positive particle) – Anti-matter electron – Same properties of an electron except it has a positive charge • Alpha Particle – Helium nucleus – 1st radioactive particle discovered by Ernest Rutherford • Gamma Radiation – High energy electromagnetic radiation Radiation Symbol 0 • Positron: e, β+ 1 4 • Alpha: He, α 2 0 • Gamma: γ 0 Section 3: Properties of Certain Types of Radiation Property Alpha Particle Beta-minus particle +2 -1 Beta-positive particle +1 Speed Largest and slowest form of radiation Faster than Speed of light alpha (same as beta-minus) Can be stopped by… Piece of paper Plastic, aluminum foil Charge Faster than alpha Plastic, aluminum foil Gamma Radiation n/a Thick lead or concrete Section 4: Isotopes • Same element, different number of neutrons • There are 2 ways to identify isotopes: – Hyphen-Notation = element – mass # • Example: oxygen – 16 – Chemical Configuration • Example: number mass 16 atomic 8 number O 2- ioniccharge Section 4, continued • Isotopes of hydrogen have special names • Deuterium and tritium are radioactive; protium is not. Section 4, continued • Why are some isotopes radioactive and others are not? – The proton : neutron ratio determines whether an isotope is radioactive • Elements with atomic # ≤ 20 prefer a 1 : 1 ratio • Elements with atomic # > 20 prefer a 1 : 1.5 ratio • Transuranium elements = – Elements with atomic # > uranium (92) – All are radioactive – In fact, all elements with atomic number > 83 are radioactive! Section 4 Example Problems 1. Write the hyphen-notation and the chemical configuration for an iron atom that has 23 electrons and 32 neutrons. Section 4 Example Problems, continued 2. Write the hyphen-notation and determine the number of protons, neutrons and 32 electrons for P. 15 Section 4 Example Problems, continued 3. Write the hyphen-notation and chemical configuration for the three isotopes of hydrogen. Assume each isotope is neutral. Section 5: Use of Carbon-14 in Radiocarbon Dating Section 6: Nuclear Reactions v Chemical Reactions Nuclear Reactions • Forms a new isotope or different element • Extremely large energy changes • Energy comes from the binding energy of the nucleus • Involves a change in the number of protons or neutrons Chemical Reactions • Forms new substances based on the elements present in the reactants • Small energy changes • Energy comes from breaking and forming chemical bonds • Involves valence electrons Section 7: Writing Nuclear Reactions Steps 1. Set up 2 equations: one using the mass (top) numbers and the other using the atomic (bottom) numbers. 2. Calculate the missing mass number. 3. Calculate the missing atomic number. 4. Use the atomic/mass #s to determine the identity of the missing particle. Example 29Mg 0e + _________ −1 12 Mass #s: 29 = 0 + _____ Atomic #s: 12 = -1 + _____ Section 8: Alpha Emission • A helium nucleus (2 p, 2 n) is emitted from the nucleus • Example: Alpha decay of 241Am Section 8: Beta Emission • A neutron is converted into a proton and electron, then the electron (β- particle) is emitted • Example: Beta decay of 14C Section 8: Positron Emission • A proton is converted into a neutron and positron, and the positron is emitted from the nucleus • Example: Positron Emission of 11C Section 8: Electron Capture • The nucleus captures an electron and combines it with a proton to form a neutron • Example: Electron capture by 7Be Section 8: Gamma Emission • Gamma rays are emitted during nuclear reactions, either alone or with other types of radiation • Gamma rays do NOT change the mass number or atomic number because they are energy not matter. 240 240 Pu* Pu 94 94 γ ray Section 9: Decay Series A series of nuclear reactions that occur until a stable nucleus is formed The first 4 nuclear reactions in the uranium-238 decay series are: 238U 4 He 2 + 234Th 234Th 0 β -1 + 234Pa 234Pa 0 β -1 + 234U 4 He 2 + 230Th 234U Section 10: Fission • Definition – heavier nuclei split apart to form lighter nuclei • Occurs in… – Nuclear power plants, nuclear bombs • Chain Reaction (definition) – neutrons produced from one reaction can hit other isotopes to start a new fission reaction • Example of Fission Reaction 1n + 235U 141Ba + 92Kr + 3 1n 92 56 36 0 0 Section 11: Nuclear Power Plant Containment Structure (A) -thick layers of concrete and steel to prevent radiation leakage Control Rods (B) -controls the rate of reaction; can be used to shut reaction down Reactor (C) -where the nuclear reactions take place Steam Generator (D) -nuclear reactions produce heat energy which is used to boil water Turbine (H) -steam runs the turbine, which causes the generator (G) to produce electricity Fuel Rods (K) -usually contain uranium-235; the fuel for the nuclear fission reaction Condenser (I) -sends cool water to the cooling tower (J) and reactor; vital to keep reactor from overheating Section 11: Nuclear Power Plant • A nuclear reactor is self-sustaining due to the chain reaction. The neutrons that are produced from one reaction cause a new fission reaction to occur. Section 12: Nuclear Power (Fission) Pros and Cons Pros • No air pollution • No greenhouse gas emissions • Low cost fuel because very little is needed • Can be done at room temperature Cons • Expensive to build and maintain • Risk of accidents • Security • Thermal pollution (warm water into streams and rivers) • Disposal of nuclear waste (must be buried for possibly thousands of years) Section 13: Fusion Reaction • Definition – light nuclei combine (fuse) together to form heavier nuclei • Occurs in… – the sun and other stars; hydrogen (fusion) bomb • Example of Fusion Reaction 2H + 3H 4He + 1n 1 1 2 0 Section 14: Fusion Pros and Cons Pros • Produces even more energy per gram of fuel than fission. • Produces less nuclear waste than fission. • Fusion fuel is easy to get. (Heavy hydrogen is found in water.) Cons • Does not sustain a chain reaction. • Requires extremely high temperatures (108 - 109 °C) and pressures. • We do not have the technology to efficiently harness the energy produced by fusion or to contain a fusion reaction.