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

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

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

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

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

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)

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

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

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

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

Chapter 4 Section 5 Homework – pg 163

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

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.

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

2A. What are three products of radioactive decay?

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

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

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

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