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NUCLEAR CHEMISTRY. Discovery of Radiation. Roentgen (1895). Studied fluorescent materials that glowed when hit with a beam of electrons.
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Discovery of Radiation Roentgen (1895) • Studied fluorescent materials that glowed when hit with a beam of electrons. • Discovered a mysterious form of radiation was given off even without electron beam. This radiation could pass through paper and other objects but not dense materials (lead, bone). • Called them X-rays
Becquerel (1896) • Studied fluorescent minerals containing uranium. • Discovered radioactivity by accident on a cloudy day: • Thought that an external source was needed to produce the mysterious radiation. • Found that uranium emits radiation without external source.
Pierre and Marie Curie Thought radioactivity was a property of heavy elements. During study, discovered new radioactive elements: Polonium and Radium. Wondered how small mass can give off large amount of energy: Explained by Einstein with E=mc2.
Rutherford • Studied radioactivity and named types of nuclear radiation. • Discovered that elements decay into other elements after emitting nuclear radiation. Called it Nuclear Decay. • Gold foil experiment revealed that the mass of an atom is concentrated in the nucleus (atom is mostly space)
Atomic Structure Recall: Atoms – consist of a positively charged nucleus, which has protons and neutrons. Isotope – atoms of the same chemical element that have a different number of neutrons. Each isotope of a given element is designated by the total number of its protons plus its neutrons. 42 59 101 1 1 2 6 8 14 92 146 238 83 127 210 2 2 4
Nuclear Forces • Electric repulsion – ________ charge particles repel each other same • Strong Nuclear Force – causes protons and neutrons to ________ each other attract • Stable Nuclei = strong nuclear force is ________ than repulsion force greater • Unstable Nuclei = strong nuclear force is ________ than repulsion force less • Have too many or too few neutrons in nucleus • Have more than 83 protons in nucleus • Will undergo radioactive decay to form a more stable nucleus
Nuclear Decay • Transmutation-One element becomes another. • Why nuclides decay • need stable ratio of neutrons to protons More than 83 protons means that the nuclei is unstable (radioactive)
Types of Radiation Charge Shielding 2+ paper • Alpha particle () • helium nucleus • Beta particle (-) • electron 1- lead • Positron (+) • positron 1+ concrete • Gamma () • high-energy photon 0
parent nuclide alpha particle daughter nuclide Alpha Emission occurs when the nucleus has too many protons which cause excessive repulsion. Numbers must balance!!
Alpha Emission Ex. Plutonium-239 undergoes alpha decay + = + 239 235 4 Atomic Mass: = + 92 94 2 Atomic #: Masses must be equal = Conservation of mass
Alpha Emission = + 210 A 4 - = = 206 210 4 A + = 2 Z 84 - = = 82 84 2 Z Ex. Polonium-210 undergoes alpha decay to produce this daughter nuclide + Atomic Mass: Atomic #: =
electron Beta Emission occurs when the neutron to proton ratio is too great.
Beta Emission = + 210 A 0 - = = 210 210 0 A + = -1 Z 84 + = = 85 84 1 Z Ex. Polonium-210 undergoes beta decay to produce this daughter nuclide + Atomic Mass: Atomic #: =
Positron Emission positron Occurs when the neutron to proton ratio is too small.
Positron Emission = + 210 A 0 - = = 210 210 0 A + = +1 Z 84 - = = 83 84 1 Z Ex. Polonium-210 undergoes positron emission to produce this daughter nuclide + Atomic Mass: Atomic #: =
electron Electron Capture occurs when the neutron to proton ratio in the nucleus is too small.
Electron Capture + = 210 0 A = 210 A + = -1 Z 84 = 83 Z Ex. Polonium-210 captures an electron to produce this daughter nuclide + Atomic Mass: Atomic #: =
Gamma Emission occurs when the nucleus is at too high an energy. • Emission of high energy electromagnetic wave.
Gamma Emission = + 210 A 0 = 210 A + = 0 Z 84 = 84 Z Ex. Polonium-210 undergoes gamma decay to produce this daughter nuclide + Atomic Mass: Atomic #: =
Write Nuclear Equations! Write the nuclear equation for the beta emitter Co-60.