Nuclear Chemistry Chapter 21A

1. Nuclear Chemistry Chapter 21A West Valley High School General Chemistry Mr. Mata

2. Standard 11d • Students know the three most common forms of radioactive decay are alpha, beta, and gamma particles.

3. Essential Question: • What are the three main types of radiation and how do they differ from each other?

4. Nuclear Reactions • Reactions that occur in the NUCLEUS. • Differ from chemical reactions. • Cannot be slowed down, sped up, or turned off.

5. Chemical Reactions vs. Nuclear Reactions • Chemical Reactions: • Atoms gain stability by attaining stable electron configurations (loss or gain of e-’s). • Nuclear Reactions: • Unstable isotopes (radioisotopes) gain stability by making changes within their nuclei. • Not affected by pressure, temp., or catalysts. • Radioisotopes have unstable nuclei.

6. Radioactivity • Stability of the nucleus: • Ratio of neutrons to protons. • Too many or few neutrons relative to the # of protons = unstable nucleus. • Out of 1500 known nuclei, 264 are stable.

7. Radioactive Decay • The process in which an unstable nucleus loses energy by emitting radiation. • Spontaneous process. • Does not need any input of energy. • Unstable radioisotopes are eventually transformed into stable (nonradioactive) isotopes of a different element.

8. Ernest Rutherford • Used U and Th in a magnetic field. • Alpha and beta particles were deflected by a magnetic field. • Gamma rays moved through the field without being affected.

9. 3 Types of Radiation • ALPHA() radiation—could be stopped by a sheet of paper • +2 charge --helium atom 42He • BETA ()radiation—could be stopped by a sheet of aluminum • -1 charge --high-speed electron

10. Types of Radiation (cont.) • GAMMA ()radiation—could be stopped by lead • No charge --no mass

11. Penetrating Ability of Types of Radiation Insert figures 18.4, 18.5

12. Tissue Damage • Tissue damage measured in mrems. • Alpha particles have little penetrating power and are not harmful unless ingested. • Beta particles are more damaging because they can penetrate further. • Gamma rays are most penetrating and can cause the most damage.

13. Radiation Detectors • Geiger Counters • Detect ionization caused by radiation. • Recorded by electronic devices (“clicks”). • Film badges • react to radiation as film exposure to light. • greater radiation = greater film exposure.

14. Background Radiation • Cosmic rays (from outer space). • Naturally sources: • air, water, soil, rocks. • 40K, 232Th, 222Rn, 238U • Artificial sources: • X-rays, nuclear medicine. • Fallout from nuclear accidents and testing. • Average dose- 100 mrem/year.

15. Uses of Radioactivity • Non-medical • tracers determine pathways & material flow. • activation analysis (cause certain elements to become radioactive). • preserve food. • C-14 dating (used to date fossils & artifacts).

16. Medical Uses of Radiation • Medical applications: • Thyroid gland uptake of 131I to diagnose thyroid disease. • Measuring blood flow. • PET (Positron Emission Topography body scan). • Treatment of tumors (chemotherapy).

17. Half-Life • Half-life (t1/2): the time required for one-half of the atoms of a radioisotope to decay into new product(s).

18. Example: Half-life • Assume there are 2.00 g of N-13. How many grams of N-13 will exist after 3 half-lives? # of half-lives Mass of N-13 0 2.00 g 1 1.00 g 2 0.50 g 3 0.25 g

19. Transmutation Reactions • Transmutation: conversion of atom of one element to atom of another element. • Some occur naturally by decay (, ). • Some artificially made in labs. • High-energy particles bombard nucleus of an atom.

20. Transuranium Elements • Elements in the periodic table with atomic numbers above 92. • None occur in nature and all are radioactive. • Synthesized in nuclear reactors and nuclear accelerators.