Unstable Nuclei and Radioactive Decay

1. Unstable Nuclei and Radioactive Decay Section 4.4

2. Radioactivity • Some substances spontaneously emit radiation – radioactivity • The rays and particles emitted are called “radiation”. • Radioactive elements change their identity – they can change into another element • They do this because the nuclei are unstable • Changes to atom’s nucleus is called a nuclear reaction Something else Dalton got wrong.

3. Radioactive Decay • Radioactive elements emit energy as radiation • This is called ‘radioactive decay’ • Unstable atoms undergo radioactive decay until they form stable atoms

4. Types of Radiation • Alpha Radiation – emitting a positively charged particle - α • Beta Radiation – emitting a negatively charged particle - β • Gamma Radiation – High energy radiation with no mass - γ

5. Alpha Radiation • Alpha radiation • Made up of Alpha particles • Alpha particles have 2 protons, 2 neutrons • Alpha particles have a 2+ charge α

6. + Nuclear Equations Nuclear Equations transmutation - an element is transformed into a new element. This can occur by natural or artificial means. loss of an a particle radium is emitting an a particle

7. Beta Radiation • Beta Radiation is fast moving electrons • Attracted to positive charged items • Charge is 1-

8. Gamma Radiation • High Energy radiation with no mass • No charge • Usually accompany alpha and beta radiation • Account for most of the energy lost during radioactive decay

10. What Makes Nuclear Stability? • Biggest factor is neutron to proton ratio • Will be discussed in Chapter 25 • Atoms with either too many or too few neutrons will be radioactive

11. γ He β 4 2 0 -1 0 0 Review • Explain how unstable atoms gain stability? • Atoms gain stability by losing energy as emitted radiation. • Complete the following table: +2 4 1/1840 -1 0 0

12. γ He β 4 2 0 -1 0 0 Review

13. Review • Classify each as a chemical reaction, nuclear reaction, or neither • Thorium emits a beta particle: • Nuclear • Two atoms share electrons to form a bond: • Chemical • A sample of pure sulfur emits heat as it slowly cools: • Neither • A piece of iron rusts: • chemical