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Chapter 7 Lesson 2

Chapter 7 Lesson 2. Isotopes and Radioactivity. Left. What ’ s the difference between the two atoms in Figure 12?. Isotopes – Different Numbers of Neutrons. What ’ s the difference between the two atoms in Figure 12?. O-17 has one extra neutron These two atoms are called Isotopes.

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Chapter 7 Lesson 2

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  1. Chapter 7 Lesson 2 Isotopes and Radioactivity

  2. Left • What’s the difference between the two atoms in Figure 12?

  3. Isotopes – Different Numbers of Neutrons • What’s the difference between the two atoms in Figure 12? • O-17 has one extra neutron • These two atoms are called Isotopes

  4. How Many Neutrons? Isotopes with more neutrons are heavier than isotopes with fewer neutrons. Lets calculate the number of neutrons in a Carbon-14 atom:

  5. Left How many neutrons? • How many neutrons are in Carbon-12 atoms? • How many neutrons are in Carbon-13 atoms?

  6. How many neutrons? • How many neutrons are in Carbon-12 atoms? • 12 – 6 = 6 neutrons • How many neutrons are in Carbon-13 atoms? • 13 – 6 = 7 neutrons

  7. What determines properties? • Chemical properties are determined by the number of valence electrons an atom has. • Valence electrons determine what type of bond an element will form. • Do isotopes have similar chemical properties??

  8. What determines properties? • Chemical properties are determined by the number of valence electrons an atom has. • Valence electrons determine what type of bond an element will form. • Do isotopes have similar chemical properties?? Yes they do, because they have the same number of electrons.

  9. What is radioactive decay? • The three isotopes of Carbon have similar properties, but C-14 is radioactive.

  10. What is radioactive decay? • When radioactive decay occurs, an unstable atomic nucleus changes into another nucleus by releasing one or more particles and energy. • Stability increases and a different element is formed. (See Figure 15 on page 303)

  11. Left Uses of Radioactive Decay • Look on page 304 at the bottom. • List 3 ways that we have found to use radioactive decay

  12. Uses of Radioactive Decay • Look on page 304 at the bottom. • List 3 ways that we have found to use radioactive decay: • Medical imaging • Detection of cancer cells • Killing of cancer cells • Preservation of food

  13. Radioactive Elements and the Periodic Table • Radioactive elements = elements that have only radioactive isotopes • Radioactive Elements are HEAVY so they are found near the bottom of the periodic table (See figure 18 below)

  14. Half-life • Isotopes decay at very different rates • Half-life= the time it takes for half of the original sample to decay • Uranium-235 has a half life of 713 million years! • How many grams would be left after another 713 million years?

  15. Left Half-life • Erbium has many isotopes: 1. How many seconds is the half-life for Er-147? 2. How much time would it take for a 100g sample of Er-145 to decay to a 25g sample? 3. How much time would it take for a 200g sample of Er-169 to decay to a 100g sample?

  16. Half-life • Erbium has many isotopes: 1. How many seconds is the half-life for Er-147? 2.5 s 2. How much time would it take for a 100g sample of Er-145 to decay to a 25g sample? (0.9 +0.9 = 1.8 s) 3. How much time would it take for a 200g sample of Er-169 to decay to a 100g sample? 9.40 days

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