Nuclear Stability and Decay What determines the type of decay a radioisotope undergoes? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Interpret Data The stability of a nucleus depends on the ratio of neutrons to protons. The region of the graph in which these points are located is called the band of stability. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Interpret Data The stability of a nucleus depends on the ratio of neutrons to protons. For elements of low atomic number (below about 20), this ratio is about 1. Above atomic number 20, stable nuclei have more neutrons than protons. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Stability and Decay A nucleus may be unstable and undergo spontaneous decay for different reasons. The neutron-to-proton ratio in a radioisotope determines the type of decay that occurs. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Stability and Decay Some nuclei are unstable because they have too many neutrons relative to the number of protons. When one of these nuclei decays, a neutron emits a beta particle (fast-moving electron) from the nucleus. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Stability and Decay Some nuclei are unstable because they have too many neutrons relative to the number of protons. When one of these nuclei decays, a neutron emits a beta particle (fast-moving electron) from the nucleus. A neutron that emits an electron becomes a proton. n 1 p + e –1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Stability and Decay Some nuclei are unstable because they have too many neutrons relative to the number of protons. When one of these nuclei decays, a neutron emits a beta particle (fast-moving electron) from the nucleus. A neutron that emits an electron becomes a proton. n 1 p + e –1 This process is known as beta emission. It increases the number of protons while decreasing the number of neutrons. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Stability and Decay Radioisotopes that undergo beta emission include the following. Cu 66 29 Zn + 30 e –1 C 14 6 N + 7 e –1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Stability and Decay Other nuclei are unstable because they have too few neutrons relative to the number of protons. These nuclei increase their stability by converting a proton to a neutron. An electron is captured by the nucleus during electron capture. Co 59 27 Ni + e 28 –1 Cl 37 17 Ar + e 18 –1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Stability and Decay A positron is a particle with the mass of an electron but a positive charge. Its symbol is e. During positron emission, a proton changes to a neutron, just as in electron capture. +1 B 8 5 Be + 4 e +1 O 15 8 N + 7 e +1 When a proton is converted to a neutron, the atomic number decreases by 1 and the number of neutrons increases by 1. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Stability and Decay Nuclei that have an atomic number greater than 82 are radioactive. These nuclei have both too many neutrons and too many protons to be stable. Therefore, they undergo radioactive decay. Most of them emit alpha particles. Alpha emission increases the neutron-to-proton ratio, which tends to increase the stability of the nucleus. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Stability and Decay In alpha emission, the mass number decreases by four and the atomic number decreases by two. Ra 226 88 Rn + He 222 86 4 2 Th 232 90 Ra + He 228 88 4 2 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Nuclear Stability and Decay Conservation of mass is in chemical reactions. Mass is not conserved during nuclear reactions. Small quantity of mass is converted into energy released during radioactive decay. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

During nuclear decay, if the atomic number decreases by one but the mass number is unchanged, the radiation emitted is A. a positron. B. an alpha particle. C. a beta particle. D. a proton. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

During nuclear decay, if the atomic number decreases by one but the mass number is unchanged, the radiation emitted is A. a positron. B. an alpha particle. C. a beta particle. D. a proton. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.