2. Unstable Nuclei & Radioactive Decay Standard: 11d, 11e Article: 105 Mastering Concepts: 112(53-58) Terms: 105 Homework: Cornell Notes: 4.4 Section Assessment: 107(23-26) 7 Stamps

3. Section 4-4 Section 4.4 Unstable Nuclei and Radioactive Decay Explain the relationship between unstable nuclei and radioactive decay. Characterize alpha, beta, and gamma radiation in terms of mass and charge.

4. element: a pure substance that cannot be broken down into simpler substances by physical or chemical means

5. radioactivity radiation nuclear reaction radioactive decay alpha radiation Unstable atoms emit radiation to gain stability. alpha particle nuclear equation beta radiation beta particle gamma rays

6. Section 4-4 Radioactivity Nuclear reactions can change one element into another element.

7. In the late 1890s, scientists noticed some substances spontaneously emitted radiation, a process they called radioactivity.radioactivity The rays and particles emitted are called radiation. radiation A reaction that involves a change in an atom's nucleus is called a nuclear reaction.nuclear reaction

8. Section 4-4 Radioactive Decay Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay. radioactive decay

9. Unstable radioactive elements undergo radioactive decay thus forming stable nonradioactive elements.

10. Section 4-4 Radioactive Decay (cont.) Alpha radiation is made up of positively charged particles called alpha particles.Alpha radiationalpha particles Each alpha particle contains two protons and two neutrons and has a 2 + charge.

11. Section 4-4 Radioactive Decay (cont.) The figure shown below is a nuclear equation showing the radioactive decay of radium-226 to radon-222.nuclear equation The mass is conserved in nuclear equations.

12. Section 4-4 Radioactive Decay (cont.) Beta radiation is radiation that has a negative charge and emits beta particles.Beta radiation Each beta particle is an electron with a 1– charge.beta particle

13. Section 4-4 Radioactive Decay (cont.)

14. Section 4-4 Radioactive Decay (cont.) Gamma rays are high-energy radiation with no mass and are neutral.Gamma rays Gamma rays account for most of the energy lost during radioactive decay.

16. Section 4-4 Radioactive Decay (cont.) Atoms that contain too many or two few neutrons are unstable and lose energy through radioactive decay to form a stable nucleus. Few exist in nature—most have already decayed to stable forms.

17. Mastering Concept 112 (53-58)

18. 53. What type of reaction involves changes in the nucleus of an atom? (4.4) 53. nuclear reaction

19. 54. Explain how energy loss and nuclear stability are related to radioactive decay. (4.4) 54. Radioactivity results when unstable nuclei emit energy in order to gain stability.

20. 55. Explain what must occur before a radioactive atom ceases to undergo further radioactive decay. (4.4) 55. A stable, nonradioactive atom must be formed.

21. 56. Write the symbols used to denote alpha, beta, and gamma radiation and give their mass and charge. (4.4) ParticleSymbolMass (amu)Charge α 4 2 He ’ 4+2 β -1 β1/1840 γ 0γ0γ00

22. 57. What change in mass number occurs when a radioactive atom emits an alpha particle? A beta particle? A gamma particle? (4.4) α, mass number decreases by 4; Β, no change in mass number; γ, no change in mass number

23. 58. What is the primary factor determining whether or not an atom is stable or unstable? (4.4) the neutron-to-proton ratio

24. Practice Quiz (872-873) Section 4-3 23

25. Section 4.4 24