Chemistry 25.2

1. Chemistry 25.2

2. 25.2 Nuclear Transformations • Radon-222 is a radioactive isotope that is present naturally in the soil in some areas. It has a constant rate of decay. You will learn about decay rates of radioactive substances.

3. 25.2 Nuclear Stability and Decay • Nuclear Stability and Decay • What determines the type of decay a radioisotope undergoes?

4. 25.2 Nuclear Stability and Decay • 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 hold the nucleus together.

5. 25.2 Nuclear Stability and Decay • More than 1,500 different nuclei are known. Of those, only 264 are stable and do not decay or change with time. These nuclei are in a region called the band of stability.

6. 25.2 Nuclear Stability and Decay

7. 25.2 Nuclear Stability and Decay • The neutron-to-proton ratio determines the type of decay that occurs. • A positron is a particle with the mass of an electron but a positive charge. During positron emission, a proton changes to a neutron.

8. 25.2 Nuclear Stability and Decay

9. 25.2 Half-Life • Half-Life • How much of a sample of a radioisotope remains after each half-life?

10. 25.2 Half-Life • A half-life (t1/2) is the time required for one-half of the nuclei of a radioisotope sample to decay to products. • After each half-life, half of the existing radioactive atoms have decayed into atoms of a new element.

11. 25.2 Half-Life

12. 25.2 Half-Life

13. Half-Life • Simulation 30 Simulate the decay of several isotopes.

14. 25.2 Half-Life Stable Isotope

15. 25.2 Half-Life • The ratio of Carbon-14 to stable carbon in the remains of an organism changes in a predictable way that enables the archaeologist to obtain an estimate of its age.

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17. 25.1

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20. for Sample Problem 25.1 Problem Solving 25.7 Solve Problem 7 with the help of an interactive guided tutorial.

21. 25.2 Transmutation Reactions • Transmutation Reactions • What are two ways that transmutation can occur?

22. 25.2 Transmutation Reactions • The conversion of an atom of one element to an atom of another element is called transmutation. • Transmutation can occur by radioactive decay. Transmutation can also occur when particles bombard the nucleus of an atom.

23. 25.2 Transmutation Reactions • The first artificial transmutation reaction involved bombarding nitrogen gas with alpha particles.

24. 25.2 Transmutation Reactions • The elements in the periodic table with atomic numbers above 92, the atomic number of uranium, are called the transuranium elements. • All transuranium elements undergo transmutation. • None of the transuranium elements occur in nature, and all of them are radioactive.

25. 25.2 Transmutation Reactions • Transuranium elements are synthesized in nuclear reactors and nuclear accelerators.

26. 25.2 Section Quiz. • 25.2.

27. 25.2 Section Quiz. • 1. During nuclear decay, if the atomic number decreases by one but the mass number is unchanged, the radiation emitted is • a positron. • an alpha particle. • a neutron. • a proton.

28. 25.2 Section Quiz. • 2. When potassium-40 (atomic number 19) decays into calcium-40 (atomic number 20), the process can be described as • positron emission. • alpha emission. • beta emission. • electron capture.

29. 25.2 Section Quiz. • 3. If there were 128 grams of radioactive material initially, what mass remains after four half-lives? • 4 grams • 32 grams • 16 grams • 8 grams

30. 25.2 Section Quiz. • 4. When transmutation occurs, the ________ always changes. • number of electrons • mass number • atomic number • number of neutrons

31. 25.2 Section Quiz • 5. Transmutation occurs by radioactive decay and also by • extreme heating. • chemical reaction. • high intensity electrical discharge. • particle bombardment of the nucleus.

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