Chap19Outlines - Chapter19 Nuclear Chemistry Lecture Outline Common Student Misconceptions This is new territory for students who have not taken

Chap19Outlines - Chapter19 Nuclear Chemistry Lecture...

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Chapter19 Nuclear Chemistry Lecture Outline Common Student Misconceptions This is new territory for students who have not taken advanced courses in physics. Radioactivity When nuclei change spontaneously, emitting energy, they are said to be radioactive . Nuclear chemistry is the study of nuclear reactions and their uses. Nucleons are particles in the nucleus: p + : proton n 0 : neutron. Mass number: the number of p + + n 0 . The mass number is the total number of nucleons in the nucleus. Atomic number: the number of p + . Isotopes have the same number of p + but different numbers of n 0 Different isotopes of the same element are distinguished by their mass numbers. Different isotopes have different natural abundances. A radionuclide is a radioactive nucleus. Atoms containing these nuclei are called radioisotopes . Nuclear Equations Most nuclei are stable. Radionuclides are unstable and spontaneously emit particles and/or electromagnetic radiation. Example: Uranium-238 is radioactive. It emits alpha particles . These are helium-4 particles. When a nucleus spontaneously decomposes in this manner, we say it has decayed ( radioactive decay ). In nuclear equations, the total number of nucleons is conserved: We can represent the uranium-238 decay by the following nuclear equation: The total number of protons and neutrons before a nuclear reaction must be the same as the total number of nucleons after reaction. Types of Radioactive Decay There are three types of radiation which we will consider: α -Radiation is the loss of ( alpha particles ) from the nucleus. β -Radiation is the loss of an electron from the nucleus. These high-speed electrons are called beta particles . γ -Radiation is the loss of high-energy photons from the nucleus. Nucleons can undergo two other types of decay: Positron emission . A positron is a particle with the same mass as an electron but an opposite sign. Electron capture . The nucleus captures an electron from the electron cloud surrounding the nucleus. Representations: He Th+ U 4 2 234 90 238 92 He 4 2
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e p+ n 0 1 - 1 1 1 0 e n+ p 0 1 1 0 1 1 n e p 1 0 0 1 1 1 + - α 4 2 In nuclear chemistry to ensure conservation of nucleons we write all particles with their atomic and mass numbers: 2 4 He and represent α -radiation. Nucleons can undergo decay: ( β -emission) (positron annihilation) (positron or β + -emission) (electron capture) Patterns of Nuclear Stability Neutron-to-Proton Ratio The proton has high mass and high charge. Therefore the proton-proton repulsion is large. In the nucleus the protons are very close to each other. The cohesive forces in the nucleus are called strong nuclear forces .
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