The nuclear Atom

1. The nuclear Atom Nuclear Chemistry

2. Radioactivity • Not all atoms are stable. • Unstable atoms break down and give off energy to become more stable. • These atoms are referred to as RADIOISOTOPES. • The energy and particles that are given off when radioisotopes break down are called radiation. • Radioisotopes break down in a series of nuclear reactions known as nuclear decay.

3. Nuclear Decay • 3 Types of Radiation • Alpha • Beta • Gamma • Type of radiation emitted is determined by the neutron to proton ratio. • Stable nuclei have a ratio that is found within the BAND OF STABILITY. (see graph p. 803) • Small atoms have a ratio of approx. 1 • Heavy atoms have a ratio of approx. 1.5

4. Alpha Radiation • Alpha Decay occurs when the nucleus is too big. • In alpha decay, an alpha particle or helium nucleus is emitted. (42 He) • 2 protons • 2 neutrons • 0 electrons • 22688 Ra  22286Rn + 42 He

5. Beta Radiation • Beta Decay occurs when there are too many neutrons relative to protons. • In beta decay, a neutron turns into a proton by giving off a beta particle or electron. (0-1e) • n0 p+ + e- • 6629 Cu  6630 Zn + 0-1e

6. Gamma Radiation • Gamma radiation or gamma rays are given off during alpha or beta decay. • Gamma rays have no mass and no charge. (γ) • Therefore, they do not alter the number of protons or neutrons in the nucleus. • 22688 Ra  22286Rn + 42 He + γ

7. Decay Equations Practice… Write the decay equation. • Uranium-238 undergoes α decay. • Bismuth-210 undergoes β decay. • Thorium-230 undergoes α and γ decay. • Lead-214 undergoes β and γ decay.

8. Nuclear Equation Practice • 63Cu + 2H → 21n + ____ • 44Ca + 1H → 44Sc + ____ • 9Be + 4He → 12C + ____ • 31P + 2H → 32P + ____ • 37Cl + ____ → 35S + 4He • ____ → 237Np + α • 214Pb → β + ____

9. Damage from Radiation • Alpha, beta, and gamma can ALL cause damage. • However, they differ in the degree and how easily you are protected.

10. Half-Life: rate of decay • All radioactive decay occurs at a steady rate. • The rate is measured in terms of how long it takes for ½ of the substance to decay. (half-life) • Each substance has its own half-life. • Carbon-14 5.73 x 103 years • Radon-222 3.8 days • Helium-6 0.802 seconds

11. Half-Life Problems • What is the half life of the graphed material? • What mass of radioisotope will remain after 9.0 hours? • How long will it take for only ¾ of the radioisotope to decay? • How long for only 3.125 grams to remain?

12. Half Life Practice • Initial mass = 64g 4 half lives Final mass = ? • Initial mass = 32g t = 8.0yr ½ life = 2.0yr Final mass = ? • Initial mass = 128g t = 5d ½ life = 24hr Final mass = ? • Initial mass = 400.0g Final mass = 50.0g ½ life = 13.6d t = ? • Initial mass = 1.0000g Final mass = 0.15625g ½ life = 2325yr t=?

13. Other Radioactive Reactions Fission and Fusion • Fission is the SPLITTING of atoms. • …what happens in a nuclear reactor • Fusion is the COMBINING of atoms. • …what happens on the sun • Both result in the release of large amounts of energy.

14. Fission • Fission occurs when certain nuclei are bombarded with neutrons. • When the atom splits, it releases additional neutrons which cause other atoms to split creating a chain reaction.

15. Fusion • Fusion occurs when small nuclei combine to create larger nuclei. • Fusion creates MORE energy than fission. • Neutrons, positrons, or electrons may be given off in a fusion reaction. • Deuterium (2H) + Tritium(3H)  Helium (4He) + neutron (1n)

16. Pros and Cons • Fission • Pro - relatively easy to control • Con - produce radioactive wastes • Fusion • Pro - produce little radioactive wastes • Con - difficult to initiate and control

17. Uses of Radioactivity • ???