2. 1 Chapter 22 - Nuclear Chemistry

3. 2 Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934).One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934). She discovered radioactive decay, the spontaneous decay of some elements into smaller pieces.She discovered radioactive decay, the spontaneous decay of some elements into smaller pieces. This is when an unstable nucleus loses energy by emitting radiationThis is when an unstable nucleus loses energy by emitting radiation

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5. 4 Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve the nucleusNuclear reactions involve the nucleus The protons and neutrons are rearrangedThe protons and neutrons are rearranged This releases a tremendous amount of energyThis releases a tremendous amount of energy This is where Dalton was wrong when he said atoms are indivisible.This is where Dalton was wrong when he said atoms are indivisible. This energy was used to hold the nucleus together and is called binding energyThis energy was used to hold the nucleus together and is called binding energy “Normal” Chemical Reactions involve electrons, not protons and neutrons“Normal” Chemical Reactions involve electrons, not protons and neutrons

6. 5 Types of Radiation Alpha Particle (α) – helium nuclei that have been emitted from a radioactive source. Two protons and two neutrons – with a charge of 2 + Alpha Particle (α) – helium nuclei that have been emitted from a radioactive source. Two protons and two neutrons – with a charge of 2 + 238 92 U → 234 90 Th + 4 2 He 238 92 U → 234 90 Th + 4 2 He Because of their large mass and charge, they do not tend to travel very far and are not very penetrating.

7. 6 Types of Radiation Beta Particle (β) – Fast moving ELECTRONS formed by the decomposition of a neutron in an atomBeta Particle (β) – Fast moving ELECTRONS formed by the decomposition of a neutron in an atom The neutron decomposes into a proton, which remains in the nucleus, and an electron, which is released.The neutron decomposes into a proton, which remains in the nucleus, and an electron, which is released. 14 6 C → 14 7 N+ 0 -1 e 14 6 C → 14 7 N+ 0 -1 e ( beta emission)

8. 7 Types of Radiation Gamma ray (γ) –high energy electromagnetic waves given off by a radioisotope.Gamma ray (γ) –high energy electromagnetic waves given off by a radioisotope. Often emitted with alpha or beta radiationOften emitted with alpha or beta radiation Have no mass or no electrical charge, so they do not alter the atomic # or massHave no mass or no electrical charge, so they do not alter the atomic # or mass.Gamma rays are extremely penetrating. They can be stopped, although not completely, by several centimeters of lead.

9. 8 Beta particles are more penetrating than alpha particles. Beta particles can pass through paper but are stopped by aluminum foil or wood. Gamma particles are the most penetrating. 2. Compare How do the characteristics of beta particles compare to those of alpha particles?

10. 9 Penetrating Ability

11. 10 Other Nuclear Particles Neutron Neutron Positron – a positive electron- proton changes into a neutron. You LOSE a proton Positron – a positive electron- proton changes into a neutron. You LOSE a proton 8 5 B → 8 4 Be + 0 +1 e 8 5 B → 8 4 Be + 0 +1 e

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13. 12 Balancing Nuclear Reactions In the reactants and products Atomic numbers must balance and Mass numbers must balance Use a particle or isotope to fill in the missing protons and neutrons

14. 13 Learning Check What radioactive isotope is produced in the following alpha bombardment of boron-10? 10 5 B + 4 2 He → ________ + 1 0 n

15. 14 Write Nuclear Equations! Write the nuclear equation for the beta emitter Co-60. 60 27 Co  60 28 Ni + ______

16. 15 Write Nuclear Equations! Write the nuclear equation for the beta emitter Co-60. 232 90 Th → 4 2 He + _______

17. 16 Half life The amount of time that it takes for ½ the mass of a radioactive nuclide to decay. Each nuclide has a half-life that is unique to that nuclide

18. 17 Examples of Half Life

19. 18 Carbon Dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, C-14, a radioactive isotope of carbon.

20. 19 Carbon Dating During its life, a plant or animal is exchanging carbon with its surroundings, so the carbon it contains will have the same proportion of C-14 as the atmosphere. Once it dies, it ceases to acquire C-14 but the C-14 within its biological material at that time will continue to decay, and so the ratio of C-14 to C-12 in its remains will gradually decrease. Because C-14 decays at a known rate, the proportion of radiocarbon can be used to determine how long it has been since a given sample stopped exchanging carbon – the older the sample, the less C-14 will be left

21. 20 Uranium Dating Can be used to date rocks that formed from about 1 million years to over 4.5 billion years ago. Half-lifeof 4.47 238 U decays to 206 Pb

22. 21 #2. An isotope of cesium (cesium-137) has a half-life of 30 years. If 1.0 mg of cesium-137 disintegrates over a period of 90 years, how many mg of cesium-137 would remain? Time Mass

23. 22 #5) After 42 days a 2.0 g sample of phosphorus-32 contains only 0.25g of isotope. What is the half-life of phosphorus-32? Time Mass

24. 23 The half-life of radon-222 is 3.823 days. What was the original mass if 0.050g remains after 7.646 days? Time Mass