1. Section 5 - pg 158 Radioactive Elements
Chapter 4
Section 5 - pg 158
Radioactive Elements

2. Pg 158
Radioactivity
In a process called radioactive decay, the atomic nuclei of unstable isotopes release fast-moving particles and energy
Isotopes: atoms with the same number of protons and different numbers of neutrons

3. Discovery of Radioactivity
Pg 159
Discovery of Radioactivity
In 1896, the French scientist Henri Becquerel discovered the effects of radioactive decay by accident while studying a mineral containing uranium
Radioactivity: a property of being able to spontaneously emit radiation

4. Pg 159
Polonium and Radium
Marie Curie noticed that some minerals containing uranium were even more radioactive than pure uranium
Minerals contained small amounts of other, highly reactive elements
Curie and husband eventually isolated two new elements, which Marie names polonium and radium

5. Types of Radioactive Decay
Pg 160
Types of Radioactive Decay
Radioactive decay can produce alpha particles, beta particles, and gamma rays
The particles and energy produced during radioactive decay are forms of nuclear radiation

6. Alpha Decay Pg 160 1st to be discovered
During Alpha decay, the radioactive nucleus loses a alpha particle (consisting of two protons and two neutrons and is positively charged = helium nucleus)
Results in a new element
Ie: thorium-232 (atomic #90) decays into radium-228 (atomic #88)

7. Beta Decay Pg 160 2nd Discovered
Atom is unstable because has too many neutrons
During beta decay, a neutron inside the nucleus of an unstable atom changes into a negatively charged beta particle and a proton
A beta particle: a fast-moving electron given off by a nucleus during radioactive decay
End result: 1 less neutron, 1 more proton
Ie : carbon-14 decays into nitrogen-14

8. Gamma Decay Pg 160 3rd discovered
Alpha and beta decay are always accompanied by gamma radiation
Gamma radiation consists of high-energy waves
Gamma radiation has no charge and does not cause a change in either the atomic mass or the atomic number

9. Effects of Nuclear Radiation
Pg 161
Effects of Nuclear Radiation
Alpha particles can be stopped by collisions with atoms (even a piece of paper will stop them)
Can cause injury to human skin similarly to a burn
Beta particles move faster, but can be blocked by an aluminum sheet 5 millimeters thick
Can travel into human body and damage cells
Gamma rays can only be stopped by a piece of lead several cm thick or a piece of concrete 1 meter thick
Can travel into human body and deliver severe damage to cells

11. Using Radioactive Isotopes
Pg 161
Using Radioactive Isotopes
Uses of radioactive isotopes include tracing the steps of chemical reactions and industrial processes, and diagnosing and treating disease
Tracers: radioactive isotopes that can be followed through the steps of a chemical reaction or an industrial process
Tracers behave the same as their nonradioactive forms
Used to find cracks in metal
Used to detect medical problems and treat some diseases

12. Chapter 4 Section 5 Homework – pg 163

13. 1A. Under what circumstances did Becquerel first notice the effects of radioactivity?

14. 1B. Look at the photo in Figure 35 (pg159)
1B. Look at the photo in Figure 35 (pg159). Explain in your own words what happened.

15. 1C. How did Becquerel’s work lead to the discovery of two new elements?

16. 2A. What are three products of radioactive decay?

17. 2B. Contrast the penetrating power of the three major types of nuclear radiation.

18. 2C. Predict the identity and mass number of the nucleus formed during the beta decay of magnesium-28

19. 3A. How can radioactive isotopes be used as tracers?

20. 3B. How is the use of radioactive isotopes in treating some forms of cancer related to certain properties of gamma radiation?