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NUCLEAR CHEMISTRY

NUCLEAR CHEMISTRY. 11 B. 10 B. Isotopes. Same element ( Z ) but different mass number ( A ). Boron-10 has 5 p and 5 n: 10 5 B Boron-11 has 5 p and 6 n: 11 5 B. Isotopes. Except for 1 1 H the mass number is always at least 2 x atomic number.

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NUCLEAR CHEMISTRY

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  1. NUCLEAR CHEMISTRY

  2. 11B 10B Isotopes • Same element (Z) but different mass number (A). • Boron-10 has 5 p and 5 n: 105B • Boron-11 has 5 p and 6 n: 115B

  3. Isotopes • Except for 11H the mass number is always at least 2 x atomic number. • Repulsive forces between protons must be moderated by neutrons. • Hydrogen: • 11H, protium • 21H, deuterium • 31H, tritium (radioactive) • Helium, 42He • Lithium, 63Li and 73Li • Boron, 105B and 115B

  4. ATOMIC COMPOSITION • Protons • + electrical charge • mass = 1.672623 x 10-24 g • relative mass = 1.007 atomic mass units (amu) • Electrons • negative electrical charge • relative mass = 0.0005 amu • Neutrons • no electrical charge • mass = 1.009 amu

  5. Radioactivity • One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934). • She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

  6. Radioactivity • Emission of particles and/or energy due to a change in the nucleus of an atom. • Nuclear Radiation also called Ionizing radiation • Measure with Geiger Counter

  7. Geiger Counter: Radiation detection

  8. Types of NUCLEAR Radiation

  9. Nuclear Reactions • Ernest Rutherford found Ra forms Rn gas when emitting an alpha particle. • 1902—Rutherford and Soddy proposed radioactivity is the result of the natural change of the isotope of one element into an isotope of a different element.

  10. Nuclear ReactionsorTransmutations • Natural Decay • Spontaneous breakdown of unstable nuclei. • Called Radioisotopes

  11. Penetrating Ability

  12. NATURAL Decay: DECAY = Fall apart Alpha DECAY Beta DECAY Positon DECAY

  13. Nuclear Reactions • Alpha emission Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2. Nucleons are rearranged but conserved [mass number (A)] Nucleons = PROTON OR NEUTRON (particle in the nucleus)

  14. Nuclear Reactions • Beta emission Note that mass number (A) is unchanged and atomic number (Z) goes up by 1. How does this happen?

  15. 207 207 Other Types of Nuclear Reactions Positron (0+1b): a positive electron K-capture: the capture of an electron from the first or K shell An electron and proton combine to form a neutron. 0-1e + 11p --> 10n

  16. Radioactive Decay Series

  17. Writing Nuclear Reactions • Parent element = Reactant • Daughter element = Product • Radioactivity = radiation produced

  18. Writing Nuclear Reactions • Law of Conservation of Mass • L. of C. of Charge • Isotopic Notation • Mass # and Nuclear Charge 146C = 147N + 0-1e

  19. Stability of Nuclei • Heaviest naturally occurring non-radioactive isotope is 209Bi with 83 protons and 126 neutrons • There are 83 x 126 = 10,458 possible isotopes. Why so few actually exist?

  20. a emission reduces Z 24395Am --> 42a + 23993Np b emission increases Z 6027Co --> 0-1b + 6028Ni Band of Stability and Radioactive Decay Isotopes with low n/p ratio, below band of stability decay, by positron emission or electron capture

  21. 3115P 21H, 63Li, 105B, 147N, 18073Ta 199F Stability of Nuclei • Out of > 300 stable isotopes: N Even Odd Z 157 52 Even Odd 50 5

  22. Binding Energy, Eb Eb = energy required to separate the nucleus into protons and neutrons. For deuterium, 21H 21H ---> 11p + 10n Eb = 2.15 x 108 kJ/mol Eb per nucleon = Eb/2 nucleons = 1.08 x 108 kJ/mol nucleons

  23. Binding Energy/Nucleon

  24. Calculate Binding Energy For deuterium, 21H: 21H ---> 11p + 10n Mass of 21H = 2.01410 g/mol Mass of proton = 1.007825 g/mol Mass of neutron = 1/008665 g/mol ∆m = 0.00239 g/mol From Einstein’s equation: Eb = (∆m)c2 = 2.15 x 108 kJ/mol Eb per nucleon = Eb/2 nucleons = 1.08 x 108 kJ/mol nucleons

  25. Half-LifeSection 15.4 & Screen 15.8 • HALF-LIFE is the time it takes for 1/2 a sample is disappear. • The rate of a nuclear transformation depends only on the “reactant” concentration. • Concept of HALF-LIFE is especially useful for 1st order reactions.

  26. Half-Life Decay of 20.0 mg of 15O. What remains after 3 half-lives? After 5 half-lives?

  27. Kinetics of Radioactive Decay Activity (A) = Disintegrations/time = (k)(N) where N is the number of atoms Decay is first order, and so ln (A/Ao) = -kt The half-life of radioactive decay is t1/2 = 0.693/k

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