chapter19_NuclearChemistry - 1 Chapter 19 Radioactivity and...

Unformatted text preview: 1 Chapter 19 Radioactivity and Nuclear Chemistry 2 Comparison Of Chemical and Nuclear Reactions Nuclear Reactions 1 Elements may be converted from one to another. 2 Particles within the nucleus, such as protons and neutrons, are involved in reactions. Chemical Reactions 1 No new elements can be produced, only new chemical compounds. 2 Usually only the outer most electrons participate in reactions. 3 Comparison Of Chemical and Nuclear Reactions Nuclear Reactions 3 Release or absorb immense amounts of energy, typically 1000 times more. 4 Rates of reaction are not influenced by external factors. Chemical Reactions 3 Release or absorb much smaller amounts of energy. 4 Rates of reaction depend on factors such as concentration, pressure, temperature, and catalysts. 4 The Nucleus Remember that the nucleus is comprised of the two nucleons : protons and neutrons. The number of protons is the atomic number. The number of protons and neutrons together is effectively the mass of the atom. 5 The Nucleus Terminology used in nuclear chemistry . 1. Nuclide refers to a nucleus with specific numbers of protons and neutrons. 2. Isotopes are nuclei that have the same number of protons but different neutron numbers. Isotopes are the same element. 6 Radioactivity Nuclides of many elements are unstable. They decay spontaneously, emitting subatomic particles and electromagnetic radiation. We refer to these nuclides as radioactive . 7 Neutron-Proton Ratios Any element with more than one proton (i.e., anything but hydrogen) will have repulsions between the protons in the nucleus. A strong nuclear force (Nuclear binding energy) helps keep the nucleus from flying apart. 8 Neutron-Proton Ratios Neutrons play a key role stabilizing the nucleus. Because they help attract other nucleons through strong nuclear force. They lack the repulsive forces associated with the positive charges of protons. Therefore, the ratio of neutrons to protons is an important factor in determining nuclear stability. Tro, Chemistry: A Molecular Approach 9 Valley of Stability (Belt of Stability) for Z = 1 ⇒ 20, stable N/Z ≈ 1 for Z = 20 ⇒ 40, stable N/Z approaches 1.25 for Z = 40 ⇒ 80, stable N/Z approaches 1.5 for Z > 83, there are no stable nuclei 10 Stable Nuclei Nuclei above this belt (or band, valley ) have too many neutrons. Some neutrons need to be converted to protons for the nuclei to be stable. 11 Stable Nuclei Nuclei below the belt have too many protons. Some protons need to be converted to neutrons for the nuclei to be stable. 12 Stable Nuclei There are no stable nuclei with an atomic number greater than 83, regardless of their neutron to proton ratio....
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