1. 25.2 Nuclear Transformations > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 25 Nuclear Chemistry

2. 25.2 Nuclear Transformations > 2 Objectives: 1. Describe what happens during nuclear decay. 2. Discuss the 3 types of nuclear radiation. 3. Compare and contrast nuclear fission and fusion. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

3. 25.2 Nuclear Transformations > 3Radioactivity Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Radioactivity - the spontaneous emission of rays or particles from certain elements, such as uranium (Marie Curie). The rays and particles emitted from a radioactive source are called nuclear radiation.

4. 25.2 Nuclear Transformations > 4Radioactivity Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Radioactivity = Radioactive decay = Nuclear reaction. Nuclear reactions begin with unstable isotopes, or radioisotopes. Atoms of these isotopes become more stable when changes occur in their nuclei. The changes are always accompanied by the emission of large amounts of energy.

5. 25.2 Nuclear Transformations > 5Radioactivity Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Radioactive decay is a spontaneous process that does not require an input of energy. If the product of a nuclear reaction is unstable, it will decay too. The process continues until unstable isotopes of one element are changed, or transformed, into stable isotopes of a different element. These stable isotopes are not radioactive.

6. 25.2 Nuclear Transformations > 6 Types of Radiation Radiation is emitted during radioactive decay. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Three types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation. Types of Radiation

7. 25.2 Nuclear Transformations > 7 Characteristics of Some Types of Radiation TypeConsists ofSymbolCharge Mass (amu) Common source Penetrating power Alpha radiation Alpha particles (helium nuclei) ,, 2+4 Radium- 226 Low (0.05 mm body tissue) Beta radiation Beta particles (electrons) ,, 1–1–1/1837 Carbon- 14 Moderate (4 mm body tissue) Gamma radiation High-energy electromagnetic radiation  00Cobalt-60 Very high (penetrates body easily) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. He 4242 e 0 –1 Interpret Data

8. 25.2 Nuclear Transformations > 8 Types of Radiation Alpha Radiation Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Some radioactive sources emit helium nuclei, which are also called alpha particles. Each alpha particle contains two protons and two neutrons and has a double positive charge. An alpha particle is written He or . 4242

9. 25.2 Nuclear Transformations > 9 Types of Radiation Beta Radiation Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. An electron resulting from the breaking apart of a neutron in an atom is called a beta particle. The neutron breaks apart into a proton, which remains in the nucleus, and a fast-moving electron, which is released. n 1010 Neutron p + 1111 Proton e 0 –1 Electron (beta particle) →

10. 25.2 Nuclear Transformations > 10 Types of Radiation Gamma Radiation Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. A high-energy photon emitted by a radioisotope is called a gamma ray. The high-energy photons are a form of electromagnetic radiation. Nuclei often emit gamma rays along with alpha or beta particles during radioactive decay. Ra + 226 88 Radium-226 Th 230 90 Thorium-230 He +  4242 Alpha particle Gamma ray → Pa + 234 91 Protactinium -234 Th 234 90 Thorium-234 e +  0 –1 Beta particle Gamma ray →

11. 25.2 Nuclear Transformations > 11 Types of Radiation Gamma Radiation Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Gamma rays have no mass and no electrical charge. Emission of gamma radiation does not alter the atomic number or mass number of an atom. Gamma rays can be dangerous because of their penetrating power. Short wavelength and high energy electromagnetic radiation.

12. 25.2 Nuclear Transformations > 12 Nuclear Stability and Decay Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The nuclear force is an attractive force that acts between all nuclear particles that are extremely close together, such as protons and neutrons in a nucleus. At these short distances, the nuclear force dominates over electromagnetic repulsions and holds the nucleus together.

13. 25.2 Nuclear Transformations > 13 Nuclear Stability and Decay Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 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. 0 +1 B 8585 Be + 8484 e 0 +1 O 15 8 N + 15 7 e 0 +1

14. 25.2 Nuclear Transformations > 14 Nuclear Stability and Decay Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What conservation of mass? mass is not conserved during nuclear reactions. An extremely small quantity of mass is converted into energy released during radioactive decay.

15. 25.2 Nuclear Transformations > 15 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 1212 A half-life (t ) is the time required for one- half of the nuclei in a radioisotope sample to decay to products. Interpret Graphs After each half- life, half of the original radioactive atoms have decayed into atoms of a new element. Half-Life

16. 25.2 Nuclear Transformations > 16Half-Life Comparing Half-Lives Half-Lives of Some Naturally Occurring Radioisotopes IsotopeHalf-lifeRadiation emitted Carbon-145.73 × 10 3 years  Potassium-401.25 × 10 9 years  Radon-2223.8 days  Radium-2261.6 × 10 3 years  Thorium-23424.1 days  Uranium-2357.0 × 10 8 years  Uranium-2384.5 × 10 9 years  Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Half-lives can be as short as a second or as long as billions of years.

17. 25.2 Nuclear Transformations > 17Half-Life Comparing Half-Lives Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Scientists use half-lives of some long-term radioisotopes to determine the age of ancient objects. Many artificially produced radioisotopes have short half-lives, which makes them useful in nuclear medicine. –Short-lived isotopes are not a long-term radiation hazard for patients.

18. 25.2 Nuclear Transformations > 18 Transmutation Reactions For thousands of years, alchemists tried to change lead into gold. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. What they wanted to achieve is transmutation, or the conversion of an atom of one element into an atom of another element. Transmutation Reactions

19. 25.2 Nuclear Transformations > 19 Transmutation Reactions Transmutation can occur by radioactive decay, or when particles bombard the nucleus of an atom. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The particles may be protons, neutrons, alpha particles, or small atoms.

20. 25.2 Nuclear Transformations > 20 Transmutation Reactions Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Ernst Rutherford performed the earliest artificial transmutation in 1919. He bombarded nitrogen gas with alpha particles. The unstable fluorine atoms quickly decay to form a stable isotope of oxygen and a proton. O + 17 8 p 1111 F 18 9 ProtonOxygen-17Fluorine-18 N + 14 7 He 4242 F 18 9 Nitrogen-14Alpha particle Fluorine-18

21. 25.2 Nuclear Transformations > 21 Nuclear Fission Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. When the nuclei of certain isotopes are bombarded with neutrons, the nuclei split into smaller fragments. This process is called fission. Nuclear Fission and Fusion

22. 25.2 Nuclear Transformations > 22 Nuclear Fission Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The figure below shows how uranium-235 breaks into two smaller fragments of roughly the same size when struck by a slow-moving neutron. More neutrons are released by the fission. These neutrons strike the nuclei of other uranium-235 atoms, which causes a chain reaction. U Uranium-235 (fissionable) 235 92 U Uranium-236 (very unstable) 236 92 Ba Barium-142 142 56 Kr Krypton-91 91 36 3 n 1010 Neutron

23. 25.2 Nuclear Transformations > 23 Nuclear Fusion Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. The energy emitted by the sun results from nuclear fusion. Fusion occurs when nuclei combine to produce a nucleus of greater mass. In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei. The reaction also produces two positrons.

24. 25.2 Nuclear Transformations > 24 Detecting Radiation Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Radiation emitted by radioisotopes has enough energy to knock electrons off some atoms of a bombarded substance, producing ions. The radiation emitted by radioisotopes is called ionizing radiation.

25. 25.2 Nuclear Transformations > 25 Detecting Radiation Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. It is not possible for humans to see, hear, smell, or feel ionizing radiation. People must rely on detection devices to alert them to the presence of radiation and to monitor its level. These devices work because of the effects of the radiation when it strikes atoms or molecules in the detector. Examples: Geiger counter (gas), scintillation counter (phosphorus)