Unit 1.3 Nuclear Chemistry

1. Unit 1.3Nuclear Chemistry 1.3-1 Types of Radioactivity

2. Learning Objectives • By the end of this section you will be able to: • Observe nuclear changes and explain how they change an element. • Express alpha and beta decay in nuclear equations. • Model the half life of an isotope. • Explain how half life is used to date materials.

3. Important Terms • Radioactivity • Alpha Particle • Beta Particle • Alpha Decay • Beta Decay • Gamma Decay • Half life • Radioactive Dating • Radioactive Decay

4. Discovery of Radioactivity • Radioactivity is the spontaneous emission of radiation by an unstable atomic nucleus.

6. Nuclear Reactions • Nuclear reactions involve the protons and neutrons found in the nucleus • During nuclear reactions a nucleus can gain or lose protons and neutrons.

7. Nuclear Reactions • Remember that the number of protons determines the identity of an element. • Changing the number of protons changed the element into another element. • During nuclear reactions atoms of one element are changed into atoms of another element

8. Nuclear Notation • Different isotopes of atoms can be represented using nuclear notation.

9. Review of Nuclear Notation • In your notebook write the following isotopes in nuclear notation. • Hydrogen-1 • Hydrogen-2 • Hydrogen-3

10. Radiation causes Radioactive Decay • Radioactive decay is the release of radiation by radioactive isotopes. • Not all radioactive isotopes decay in the same way. • Different types of decay change the nucleus in different ways. • The three types of decay are: • Alpha • Beta • Gamma decay

11. Radioactive ALPHA Decay • Alpha decay is the release of alpha particles (2 protons and 2 neutrons). • Alpha particles are helium nuclei consisting of two protons and two neutrons. • Alpha particles are represented as or α.

12. Radioactive ALPHA Decay • Alpha particles, which are large in size, collide with objects around them. • Do not penetrate very deeply • Are easily stopped by a thin layer of material.

13. Radioactive ALPHA Decay • Alpha decay causes the decaying nucleus to lose 2 protons and 2 neutrons. • This means: • the mass # decreases by 4 (2P and 2N) • The atomic # decreases by 2 • Examples • ParentDaughter alpha particle

14. Equation for Radioactive ALPHA Decay • The parent element turns into a daughter element with a mass number 4 less and an atomic number 2 less than the parent! • Does this reaction demonstrate the law of conservation of matter? • How can we check it? Explain

15. ALPHA Emission Two protons and neutrons are lost The protons and neutrons leave as an alpha particle. + Energy!

16. Radioactive Alpha Decay • Write the equation for alpha decay for the following particle in your notebook. • Thorium-230

17. Radioactive BETA Decay • Beta decay is the release of beta particles from a decaying nucleus. • A beta particle is a high energy electron with a 1- charge. • Beta particles are written as β- or • Beta particles pass more easily through matter than alpha particles and require sheets of metal, blocks of wood or specialized clothing to be stopped.

18. Radioactive BETA Decay • The electron released during beta decay is not one of the original electronsthat existed outside the nucleus. • The beta particle (electron) is produced by the change of a neutron into a proton and an electron. Mass# is same! • Parent Daughter Beta (add P+) (sub e-)

19. Equation for Radioactive BETA Decay • The parent nucleus turns into a daughter with an atomic number 1 greater. • The mass number stays the same.

20. BETA Emission • A neutron becomes a proton (which stays in the nucleus) and electron (which is ejected from the atom). • ADD A PROTON and LOSE an ELECTRON + ENERGY

21. Radioactive BETA Decay • Write the equations for beta decay for the following particles. • Magnesuim-27 • Sulfur-35

22. Radioactive Gamma Decay • Gamma decay is the release of gamma rays from a nucleus. • A gamma ray is a high energy form of electromagnetic radiation with out a change in mass or charge.

23. Radioactive GAMMA Decay • Gamma rays have high penetrating ability and are very dangerous to living cells. • To stop gamma rays thick blocks of lead or concrete are needed.

24. Radioactive GAMMA Decay • During gamma decayonly energy is released! • Gamma decay does not generally occur alone, it occurs with other modes of decay. (alpha or beta)

25. Equation for Radioactive GAMMA Decay with Beta or Alpha Decay • When gamma decay is expressed in an equation it is expressed as γ. • Electron from beta decay is captured to cause gamma particle to emit. • The following equation shows both gamma and alpha decay occurring.

26. GAMMA Emission with Beta decay Beta emission Co-60  Ni-60 + Beta e-  Ni-60 + gamma photon (particle of radiation) (excited state)

27. Quiz!! PLEASE DO NOT WRITE THE QUESTIONS! Each correctly answered question is worth 1 point! • What are the three types of decay? • Explain what occurs to the element in each type of decay, be specific. • A. B. C. • Which type of decay is least harmful to living cells. • Which is most harmful? • If Uranium-238 alpha decays, what would the decay equation be?

28. Answers to quiz questions • Alpha, beta and gamma • Alpha- gives off alpha particle which is 2 protons and 2 neutrons. It reduces the atomic number by 2 and the mass by 4 so becomes a new element Beta- a neutron becomes a proton and an electron and gives off the electron, it adds 1 to the atomic number but leaves the mass number the same so a new element is formed Gamma- just a gamma ray, pure electromagnetic radiation (energy) 3. Alpha 4.Gamma 5 238 U -> 234 Th + 4 He 92 90 2

29. Nuclear Equations: What type of decay is Represented? Fill in the blanks

30. Nuclear Equations: try these!

31. Radioactive Decay • Radiation can be detected with Geiger counters and scintillation counters. • Geiger counters detect ionizing radiation. • Scintillation counters register the intensity of radiation by detecting light.

32. Rate of Radioactive Decay • It is impossible to predict when a specific nucleus in a sample of radioactive material will undergo decay. • The rate of overall decay is constant so that it is possible to predict when a given fraction of a sample will have decayed.

33. Half-Life • Half-life is a term used to describe the time it takes for half of a given amount of a radioactive isotope to decay. • Half-life varies greatly depending on the isotope

35. Half-life: How long is it?

36. Half-Life and Radioisotope Dating • Radioactive decay has provided scientists with a technique for determining the age of fossils, geological formations and human artifacts. • Four isotopes are commonly used for dating objects • Carbon-14 • Uranium-238 • Rubidium-87 • Potassium-40

37. Half-Life and Radioisotope Dating;C-14 • Carbon-14 Dating • All organisms take in carbon during their lifetime. • When organisms die they stop taking in carbon. • Most carbon that organisms take in is stable (Carbon-12 or Carbon-13). • About one atom in a million is Carbon-14. • While the organism is alive the amount of Carbon-14 in its tissues remains constant. • After the organism dies no more Carbon-14 is taken in and the amount begins to decline at a predictable pace. (half-life of C-14=5730 years)

38. Half-Life of Carbon-14

39. Half-Life and Radioisotope Dating • The half-life of Carbon-14 is 5730 years. • Objects greater than 60,000 years old cannot be dated using this method because the amount of Carbon-14 that remains is too small to be detected. • Objects greater than 60,000 years old are dated using: • Uranium-238 (t½ = 4.5 billion years) • Rubidium-87 (t½ = 48 billion years) • Potassium-40 (t½ = 1.25 billion years)

40. Radioactive Decay Series: U-238