1. CHAPTER 25 Nuclear Chemistry

2. Radioactivity Marie and Pierre Curie –S–S–S–Studied uranium salts –F–F–F–Found that uranium emitted rays of particles even without the addition of outside energy Coined the term, RADIOACTIVITY

3. Pierre & Marie Curie

4. Radioactivity The process by which the nucleus of an atom emits particles and rays. Radiation The rays and particles emitted by a radioactive source.

5. Nuclear Reactions Involve the nucleus of unstable atoms Involve the nucleus of unstable atoms –This means neutrons and protons are involved! Unstable atoms are called radioisotopes Unstable atoms are called radioisotopes The changes in the nuclei of radioisotopes are accompanied by large amounts of energy. The changes in the nuclei of radioisotopes are accompanied by large amounts of energy. Cannot be slowed down or sped up by outside factors! Cannot be slowed down or sped up by outside factors!

6. The stability of an atom depends on it’s neutron-to-proton ratio!

7. Atom Builder Atom Builder

8. Nuclear reactions are different from chemical reactions!

9. Chemical Reactions Atoms gain stability by adding, losing, or sharing electrons Atoms gain stability by adding, losing, or sharing electrons Affected by temperature, pressure, or the presence of catalysts. Affected by temperature, pressure, or the presence of catalysts.

10. Characteristic Chemical Reaction Nuclear Reaction Involves Nuclei Involves Electrons Rate can be changed Emits energy How do nuclear reactions differ from chemical reactions?

11. How did Marie & Pierre’s discovery affect Dalton’s findings? They disproved Dalton’s Theory by saying that atoms are NOT indivisible. They disproved Dalton’s Theory by saying that atoms are NOT indivisible. Particles from a radioisotope are separated from the nucleus during radioactive decay. Particles from a radioisotope are separated from the nucleus during radioactive decay.

12. Let’s Review! The process by which unstable atoms give off rays of particles is called: Radioactivity!

13. What is the term for rays and particles given off by a radioactive source? Radiation

14. What’s another word for an unstable isotope? Radioisotope

15. Name three differences between a chemical reaction and a nuclear reaction: 1.2.3.

16. Radiation is emitted during radioactive decay

17. There are 3 types of radiation: Alpha Radiation Alpha Radiation Beta Radiation Beta Radiation Gamma Radiation Gamma Radiation

18. Alpha Radiation Unstable nucleus emits a Helium atom Unstable nucleus emits a Helium atom –2 protons and 2 neutrons The mass number of the The mass number of the original atom decreases by 4 The atomic number of the original atom decreases by 2 The atomic number of the original atom decreases by 2

19. An example of alpha radiation: The symbol for helium is: The symbol for helium is: He (2 protons & 2 neutrons) U Th + He

20. alpha radioactivity corresponds to the emission of a helium nucleus, a particularly stable structure consisting of two protons and two neutrons, called an a particle.

21. The Band of Stability

22. Facts about alpha particles: They are the nuclei of helium atoms They are the nuclei of helium atoms They have two protons, so they have a postitive charge They have two protons, so they have a postitive charge They can be sheilded by paper and clothing They can be sheilded by paper and clothing They are harmful if ingested They are harmful if ingested

23. Beta Radiation The weak nuclear force is overcome and nuclear particles begin to break. The weak nuclear force is overcome and nuclear particles begin to break. If a neutron breaks apart = electron and a proton. If a neutron breaks apart = electron and a proton. These are the symbols you need to know: These are the symbols you need to know: Electron= e Proton = H Neutron = n Neutron = n

24. Beta Radiation Continued: When the neutron breaks, the proton stays in the nucleus When the neutron breaks, the proton stays in the nucleus The electron, which is fast moving, is released from the atom The electron, which is fast moving, is released from the atom Here’s what happens: Here’s what happens: n H + e n H + e

25. When there are too many neutrons, the atom becomes stable by splitting a neutron. How does this change the atomic number of the original atom?

26. A little more on Beta radiation: Look what happens to carbon-14: Look what happens to carbon-14: C N + e C N + e When a neutron in carbon splits, a proton is gained, changing carbon’s atomic # to 7—which means it’s not Carbon, anymore! It’s changed to Nitrogen. When a neutron in carbon splits, a proton is gained, changing carbon’s atomic # to 7—which means it’s not Carbon, anymore! It’s changed to Nitrogen. The left-over electron is released from the atom! The left-over electron is released from the atom! This happens when there are too many neutrons! This happens when there are too many neutrons!

27. Positrons (still a part of Beta radiation) A positron occurs when a proton is converted into a neutron. A positron occurs when a proton is converted into a neutron. This occurs when the nucleus of a radioisotope has too many protons for the number of neutrons! This occurs when the nucleus of a radioisotope has too many protons for the number of neutrons! Cl S + Cl S +

28. So when there are too many protons, a proton splits and a positron is emitted. What does losing a proton do to the atomic # of the original atom?

29. Facts about Beta particles: They have less charge than alpha particles. They have less charge than alpha particles. They have less mass, so they’re more penetrating. They have less mass, so they’re more penetrating. –They can pass through paper but can be stopped by aluminum foil or wood. They can be electrons (β-) or positrons (β+) They can be electrons (β-) or positrons (β+)

30. A proton changed into a neutron, beta+ radioactivity, characterized by the emission of positron.

31. The Band of Stability

32. Transformation of a neutron into a proton, beta- radioactivity, characterized by the emission of an electron.

33. The Band of Stability

34. Gamma Radiation Gamma rays are high-energy photons Gamma rays are high-energy photons They are electromagnetic They are electromagnetic Have no mass Have no mass Have no charge Have no charge Are extremely penetrating & harmful Are extremely penetrating & harmful Can be stopped by several meters of concrete or centimeters of lead Can be stopped by several meters of concrete or centimeters of lead

35. Gamma Rays cont’d. Nuclei often emit alpha or beta particles along with gamma rays: Nuclei often emit alpha or beta particles along with gamma rays: Th Ra + He + γ

36. gamma radioactivity is not related to a transmutation of the nucleus. It results in the emission, by the nucleus, of an electromagnetic radiation, like visible light or X-rays, but more energetic. gamma radioactivity can occur by itself or together with alpha or beta radioactivity.