Radioactivity and Nuclear Reactions

1. Radioactivity and Nuclear Reactions Chapter 18 in the Glencoe Textbook

2. What do you remember about atoms? • The nucleus contains _________& _________. • Most of the volume of the atom is _______________. • Most the mass of the atom is located in the __________. • Draw a picture of a helium atom. (Sugar grain-10m atom analogy)

3. The Nucleus • What keeps the __ protons and the ______ neutrons together in the nucleus? • The electric force between particles make them ________ each other. • The _________ force makes them attract each other. • _______ times stronger than the electric force • Only works over very _________ distances

4. The Nucleus

5. The Nucleus’ Forces • All nuclei have repulsion due to _______ force and attraction due to __________ force. Small nuclei have few protons ___________ each other, so the strong force is much ______________ than the total electric force. Large nuclei have many protons creating a large total ___________ force of repulsion. The strong nuclear force is less because the distance is ____________ in the large nucleus.

6. Radioactivity • When the strong nuclear force is able to keep the nucleus together, the atom is _________. • When the electric force of repulsion is _______ than the strong nuclear force, the atom decays giving off ________ & _____. • Called radioactivity

7. Radioactivity • So which atoms would you expect to be radioactive? • All with atomic number above 83 • Atomic number above 92 are so unstable that they don’t exist in nature! • Some small nuclei can also be radioactive, and isotopes can be stable or unstable. • What do you remember about isotopes?

8. Radioactive Isotopes • When the number of protons and neutrons are almost _________ in smaller atoms, the nucleus is stable. • In heavier stable atoms, the ratio of neutrons to protons is about 3:2. • When the nucleus has too ______ or too _____ neutrons compared to the # of protons, the atom is unstable/radioactive.

9. How to write nuclear symbols Mass number Symbol Atomic number Examples: C-12

10. How was this discovered? • 1896, Henri Becquerel left U salt in a desk drawer with a photographic plate • U salt darkened the plate • He thought invisible rays/radiation had darkened the plate. • 1898 Marie & Pierre Curie discovered radioactive elements Po & Ra

11. Nuclear Decay • When an unstable nucleus decays, particles and energy called nuclear _______________ are emitted from it. • Three types of nuclear radiation are • Alpha • Beta • Gamma (Named for the first 3 Greek letters of the alphabet)

12. 3 types of radiation

13. SHIELDING from radiation

14. Transmutation • Unstable atoms decay until a stable atom forms. • When alpha and beta radiation are released, the identity of the atom changes. • Called transmutation • Only happens in nuclear rxns, not ordinary chem rxns • Use the symbols for the type of radiation to determine the ID of the new element

15. Transmutation • Alpha decay • One product must be a He nucleus • Website animation • Example: U-238 • Example: Po-210

16. Transmutation • Beta decay • One product must be an electron 0-1e • Website animation • Example: C-14 • Example: I-131

17. Transmutation • Gamma radiation • DOES NOT CAUSE TRANSMUTATION • Usually accompanies alpha and beta decay • Website animation

18. Half-Life • Unstable atoms decay at different rates. • Some take seconds and some take billions of years • The time required for half of the atoms in a radioactive sample to decay is called the half-life of the isotope. (Stand/radioactive-sit/stable activity) • Link to half- life website • See activboard program for ½ life problems • Half-life experiment

19. Radioactive Dating • What did you learn from the website?