1. Nuclear Chemistry

2. Nuclear Reactions  Chemical reactions  What can NOT change in a chemical reaction?  Nuclear Reactions: changes that occur in the nucleus of an atom  The nucleus is unstable!!  Most atoms have unstable nuclei.

3. Why are some stable, while others are not?  Primary Reason:  ratio of the neutrons to the protons (n/p)  An atom is most stable when ratio is 1:1  The maximum ratio of stability is around 1.5 : 1

4. RadioactivityRadioactivity  An unstable nucleus emits rays and particles, called radiation, to become stable  The process is called radioactivity  Gain stability by LOSING energy  Discovery dealt a deathblow to Dalton’s theory of indivisible atoms

5. Types of Radiation  Alpha particle (  )  helium nucleus paper 2+  Beta particle (  -)  electron 1- lead  Gamma (  )  high-energy photon 0

7. 3 Radioactive Particles  1. Alpha Particle (+)  It travels about 1/10 the speed of light (slowest) It is the largest, most massive particle  It is the most dangerous if ingested  It has the least penetrating ability - paper can stop this particle

8. 3 Radioactive Particles  2. Beta Particle (-)  Fast accelerated electron  Ejected when a neutron is converted to a proton in the nucleus  Travels 1/4 the speed of light.  It is lighter and faster than the alpha particle.  Average penetrating ability - can be stopped by heavy clothing

9. 3 Radioactive Particles  3. Gamma Ray  Not a particle; it is high energy electromagnetic radiation  Has no mass and no charge.  Always accompanies either beta or alpha radiation.  Travels at the speed of light.  Highest penetrating ability - can be stopped by heavy shielding such as lead.

10. Radioactive Particles Summary

11. Nuclear Decay  Alpha Emission parent nuclide daughter nuclide alpha particle Numbers must balance!!

12. Nuclear Decay  Beta Emission  A neutron is converted in the nucleus of an atom  A new atom is formed whose atomic number is increased by 1

13. Nuclear Decay  Gamma Emission  Always accompanies alpha and beta emissions.  Transmutation  One element becomes another.

15. Half-lifeHalf-life  Half-life (t ½ )  Time required for half the atoms of a radioactive nuclide to decay.  Shorter half-life = less stable.

16. So, what does this mean?  Let’s say you have 100 g of radioactive C- 14. The half-life of C-14 is 5730 years.  How many grams are left after one half- life?  How many grams are left after two half- lives? 50 g 25 g

17. Common Radioisotopes IsotopeHalf-LifeRadiation Emitted Carbon-145,730 years  Radon-2223.8 days  Uranium-2357.0 x 10 8 years  Uranium-2384.46 x 10 9 years 

18. Half-lifeHalf-life r :final mass i :initial mass n :# of half-lives  To find the remaining amount…

19. More Half-Life Equations  Total time passed (p) = n x t 1/2  To find the half-life  t 1/2 =  To find the # of half lives that have passed…  n =

20. Half-lifeHalf-life  Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s? GIVEN: t ½ = 5.0 s i = 25 g r = ? p = 60.0 s n = 60.0s ÷ 5.0s =12 WORK : r = i (0.5 ) n r = (25 g)(0.5) 12 r = 0.0061 g

21. You try it!  If the half life element A is 3 hours and you have 90 grams of it, how many grams would be left after 9 hours?

22. F ission  splitting a nucleus into two or more smaller nuclei  1 g of 235 U = 3 tons of coal

23. F ission  chain reaction - self-propagating reaction

24. FusionFusion  combining of two nuclei to form one nucleus of larger mass  thermonuclear reaction – requires temp of 40,000,000 K to sustain  1 g of fusion fuel = 20 tons of coal  occurs naturally in stars