1. Nuclear Chemistry Remember: Isotope = vary in number of neutrons, so mass of isotopes are different Written as: C-12 or 12 6 C

2. 2 Radioactivity Result of unstable nuclei Nucleons: particles in the nucleus, n 0 and p + Radioisotopes: atoms that containing radioactive nuclei (or radionuclides) Nuclear reactions or equations: express products of radioactive decay, fusion, or fission Radioactive decay: process in which a radionuclide spontaneously decomposes

3. 3 Important Scientists Henri Becquerel –F–First to discover radiation in 1896 (he passed this on to one of his graduate students = Marie Curie) Marie and Pierre Curie –A–Able to isolate and research radium from uranium (also Polonium) Ernest Rutherford –D–Discovered radioactive emissions in an electric field –H–He determined some particles were positive and others were negative –T–This came before the Gold Foil Experiment

4. 4 Most common types of radiation (Rutherford) 1.Alpha Particle = ( (( (ά) = large, positive particle known as today’s helium nuclei- least penetrable 2. Beta particles = ( (( (β) = lighter and faster negative particle (today’s electron) - about 100 times more penetrable than alpha particles 3. Gamma rays = ( (( (γ) = neutral emission, extremely high energy radiation. Unaffected be an electrical field - most penetrable

5. 5 Other Nuclear Particles (for balancing) NeutronNeutron Positron – a positive electron Positron – a positive electron Proton – usually referred to as hydrogen-1 (called protium)Proton – usually referred to as hydrogen-1 (called protium) DuetriumDuetrium TritiumTritium 2 1 H 3 1 H

6. 6 Let’s spend time looking at these emission types through nuclear chemical reactions!

7. 7 5 main types of Nuclear Reactions 1. Alpha emission 2 and 3. Beta 4. Electron Capture 5. Gamma Radiation Beta Emission Positron emission

8. 8 1. Alpha Emission TypeSymbolDescription Travels in air… Ex: alpha  or energized He nucleus He 4 2+ 2 A few cm; cannot penetrate human skin U 238 92 He 4 2 Th 234 90 +

9. 9 Alpha decay

10. 10 You try! Results that mass number (A) goes down by 4 and atomic number (Z) goes down by 2. Nucleons (nuclear particles… protons and neutrons) are rearranged but conserved 211 83 Bi  4 2 He + __________

11. 11 Beta emission : 2 Types : Positron and Beta particle (Beta emission) Let’s look at a Beta particle emission 1st –B–B–B–Beta particle have all properties of electrons (no mass, negative charge) –C–C–C–Created by the conversion of a neutron in the nucleus to a proton and an electron N0     p+ + e-

12. 12 Ex: Same as: beta  or High energy electron e 0 ~300 cm; can penetrate skin, but rarely I 131 53 Xe 131 54 e 0 + n 1 0 p 1 1 e 0 + A neutron converts to a proton and electron 2. Beta emission

13. 13 You Try! Results mass number (A) is unchanged and atomic number (Z) goes up by 1. Important: What changes? Losing a neutron but gaining a proton so mass # stays the same. Atomic # increasing because you’ve added a proton! 209 82 Pb  0 -1 e+ _________________

14. 14 Ex: Same as: positron Antimatter (positively charged) e; collides with e- and both are annihilated as gamma rays are created e 0 1 C 11 6 B 5 e 0 1 + p 1 1 n 1 0 e 0 1 + A proton converts to a positron and neutron Positron ( 0 +1 β): a positive electron 3. Positron (positron emission)

15. 15 You Try 58 29 Cu  0 +1 e+______________ So what is an antiparticle = + = a proton in the nucleus is converted into a neutron and a positron Neutron remains in nucleus and positron is ejected (product)

16. 16 Ex: Same as: Electron capture Capture of inner shell e- by nucleus Rb 81 37 Kr 81 36 + p 1 1 n 1 0 A proton and electron convert to a neutron e 0 e 0 e 0 + 4. Electron Capture

17. 17 You Try! 68 32 Ge + 0 -1 e  _____________ Notice: this is the only reaction that has the particle as a reactant! Electron Capture: E- combines with a proton to form a neutron Result: atomic # decreases by one and the mass # remains the same (element changes)

18. 18 Ex: gamma  or photon  0 0 Very far; can be stopped by ~5 cm of Pb Pu 244 94 +  0 0 Pu 244 94 * Represents energy emitted (i.e., radiation) when nucleons in an unstable radionuclide reorganize to become more stable Usually not written in a nuclear reaction. 5. Gamma Radiation

19. 19 Balancing only: A proton, neutron, or isotope of hydrogen can balance a nuclear reaction as well Example: 1 0 n + 35 17 Cl  34 16 S + _________ 2 1 H 12 6 C+ 238 92 U  246 98 Cf+ _____ 4 1 0 n

20. 20 Nuclear stability Strong nuclear force: pulls nucleons together to form nuclei (actually acts on quarks) Weak nuclear force: responsible for changes in favor of quarks Quarks = elementary particle of matter that combines to form composite particles like protons and neutrons Nuclei become unstable (radioactive) if the neutron- to-proton ratio “strays” too far from “normal range” * Nuclear shell model: when p+ and n 0 fill nuclear shells, atoms are unusually stable: “Magic numbers” 2, 8, 20, 28, 50, 82, 126

21. 21 A radionuclide will decay until a stable ratio exists: helps predict what form of radiation will occur to become stable If too many n, n will be converted to p by  emission. If too few n, p will be converted to n by positron emission or electron capture. Nuclei with p ≥ 84 undergo  emission 1 Beta emission Positron or e- capture Alpha

22. 22 Rates of Decay Half-life (t ½ ): Time for ½ a radioactive (i.e., having an unstable p/n ratio) material to decay (form 2 or more stable atoms)

23. 23 HALF-LIFE is the time that it takes for 1/2 a sample to decompose. The rate of a nuclear transformation depends only on the “reactant” concentration. Why does it go through radioactive decay? Nuclear Stability!

24. 24 Decay of 20.0 mg of 15O. What remains after 3 half- lives? After 5 half-lives?

25. 25 For each duration (half-life), one half of the substance decomposes. For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234 Geiger Counter After 3.6 days > 25 grams (50% of original 50 g) After 7.2 days > 12.5 grams (75% of original 50 g) After 10.8 days > 6.25 grams (87.5% of original 50 g)

26. 26 Key: –Y–You can solve these problems by dividing by 2 in the correct number of half-lives Ex: 50g÷2=25g 25g÷2=12.5g 12.5g ÷2=6.25g –O–Or use ½ lives, notice in the above problem 1 st half life = 25g remains(50g x ½ ), 2 nd half life = 12.5g remains (50g x ½ x ½ ), and 3 rd half life 6.25g remains (50 x ½ x ½ x ½ ), etc.. –U–Use formula: fraction x original = remains (half lives) (g) (g) –R–READ QUESTIONS CAREFULLY!

27. 27 If you start with 64 g of a material with a half-life of 10 years, how much will be left at the end of 40 years? Fraction x original = remains ( ½ x ½ x ½ x ½ ) x 64g = 4g remain 40÷10= 4 half lives The half-life of Iodine-125 is 60 days. If the original sample had a mass of 50.0g, how much is left after 360 days? (360 ÷60=6 half lives) Fraction x original = remains ( ½ x ½ x ½ x ½ x ½ x ½ ) x 50.0g =.78g

28. 28 Mass-energy relationships  E =  m c 2 (mass in kg) Mass → energy MM ass lost during radioactive decay is released as energy Energy → mass MM ass defect (  m): mass difference between a nucleus and its constituent nucleons; the nuclear bonding energy must be added to a nucleus to break it into its nucleons WW hen energy is added, the nucleons separate and gain mass

29. 29 Fission & Fusion Fission: splitting of a nucleus; some mass is lost, which results in release of energy (ex: nuclear power plants, “atomic” bombs) Ba + 139 56 Kr + 94 36 3 n + energy 1 0 U 235 92 n + 1 0

30. 30 Fusion: combination of 2 nuclei; some mass is lost, which results in release of energy (ex: stars, “H” bombs) H + 3 1 H 2 1 He + 4 2 n 1010 + energy