: When electrons bombarded surface of certain materials, invisible rays were emitted

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1 Nuclear Chemistry

2 Nuclear Reactions 1. Occur when nuclei emit particles and/or rays. 2. Atoms are often converted into atoms of another element. 3. May involve protons, neutrons, and electrons 4. Associated with large energy changes. 5. Reaction rate is not normally affected by temperature, pressure, or catalysts.

Wilhelm Roentgen 1845-1923 1895: When electrons bombarded

3 Wilhelm Roentgen : When electrons bombarded surface of certain materials, invisible rays were emitted

Henri Becquerel 1852-1908 studied minerals that when exposed to

4 Henri Becquerel studied minerals that when exposed to sunlight, emit light phosphorescence discovered uranium salts (pitchblende)

5 Marie Curie Marie & Pierre Curie isolated components emitting rays identified Po & Ra

6 MORE HISTORY Rutherford ( ) identified alpha, beta, and gamma radiation

7 TYPES OF RADIATION DECAY 1. Alpha ( ) 4 2 He, helium nuclei Blocked by paper; 6.64 x kg Slow moving due to mass and charge! 2. Beta ( ) 0-1 or 0-1e, electrons Blocked by metal foil; 9.11 x kg Fast moving Emitted from a neutron of an unstable nucleus Insignificant mass compared with mass of nucleus Greater penetrating power than alpha particles

8 TYPES OF RADIATION DECAY 3. Gamma ( ) 0 0, photons Not completely blocked by lead or concrete; 0 kg High energy electromagnetic radiation Almost always accompanies alpha and beta radiation

9 Radioactive Decay

10 NUCLEAR STABILITY Atoms go through different types of nuclear decay to become more stable. Correlated with atom s neutron-toproton ratio. < 20 atomic number most stable

11 ALPHA DECAY All nuclei with more than 83 protons decay spontaneously

12 BETA DECAY Instability of isotope due to too many neutrons relative to its number of protons.

13 POSITRON EMISSION Positron is a particle with the same mass as an electron but the opposite charge 0 1 or 0 1e During emission, a proton in the nucleus is converted to a neutron and a positron 1 1p --> 1 0n + 0 1

14 ELECTRON CAPTURE Nucleus of an atom draws in a surrounding electron Captured electron combines with a proton to form a neutron 1 1p + 0-1e --> 1 0n

15 PROBLEM What particle is formed when polonium-210 undergoes alpha decay? Po --> 4 2He +

16 PROBLEM What particle is formed when polonium-210 undergoes alpha decay? Po --> 4 2He ? How did I get ?

17 PROBLEM What particle is formed when polonium-210 undergoes alpha decay? Po --> 4 2He ? How did I get ? The numbers must add up the same on both sides of the equation (top # s =, and bottom # s =)

18 PROBLEM What particle is formed when polonium-210 undergoes alpha decay? Po --> 4 2He ? How do you determine the element? By atomic number!

19 PROBLEM What particle is formed when polonium-210 undergoes alpha decay? Po --> 4 2He Pb How do you determine the element? By atomic number!

20 PROBLEM What would the decay process of iodine- 131 into xenon-131 look like?

21 PROBLEM What would the decay process of iodine- 131 into xenon-131 look like? I --> Xe +?

22 PROBLEM What would the decay process of iodine- 131 into xenon-131 look like? I --> Xe + 0-1? What type of radiation: 0-1?

23 PROBLEM What would the decay process of iodine- 131 into xenon-131 look like? I --> Xe What type of radiation: 0-1? Beta!

24 RADIOACTIVE SERIES A series of nuclear reactions that begins with an unstable nucleus and results in the formation of a stable nucleus.

25 HALF-LIFE Time required for one-half of a radioisotope s nuclei to decay into its products. Exponential decay! Strontium-90 has a half-life of 29 years. So, if you had 10 g of this, in 29 years you would have 5 grams left.

26 HALF-LIFE Amount remaining = (initial amount)(1/2) n n is equal to the number of half lives that has passed OR Amount remaining = (initial amount)(1/2) T/t 1/2 T is equal to the elapsed time and t 1/2 is the duration of the half-life

27 RADIOCHEMICAL DATING Process of determining an age of an object by measuring the amount of a certain radioisotope remaining in that object Uranium Half-life of 4.5 c 10 9 years Meteorites; have estimated age of solar system at 4.6 x 10 9 years Carbon dating 14 6C ---> 14 7N Half-life of 5730 years Limited to accurately dating objects up to 24,000 years of age

28 Fission and Fusion of Atomic Nuclei

29 NUCLEAR FISSION Heavier atoms (mass # > 60) tend to fragment into smaller atoms to increase their stability This is accompanied by a very large release of energy Product particles will continue a chain reaction. Used in nuclear power plants.

30 NUCLEAR FUSION Binding together two light (mass # < 60) and less stable nuclei Capable of releasing very large amounts of energy Where does Fusion take place naturally.the sun! Requires temperatures of 40,000,000 K! Can achieve this by atomic explosion (not safe!) Don t have materials capable of withstanding these high temperatures

31 ATOMIC BOMB Utilizes principles of fission (uncontrolled!) Equal to effect of 20,000 tons of TNT

32 HYDROGEN BOMB Never used in warfare Explosive force 1000 X greater than atomic bomb Fission reaction triggers a fusion reaction of hydrogen isotopes (deuterium and tritium) Equal to 15 million tons of TNT

33 USES OF RADIATION Neutron activation analysis Determine quality of silicon wafers used in computers Radiotracers Trace biological pathways PET Imagery used in medical diagnoses Radiation to kill cancer cells Irradiation of meats, fruits

da u g ht er + radiation

da u g ht er + radiation RADIOACTIVITY The discovery of radioactivity can be attributed to several scientists. Wilhelm Roentgen discovered X-rays in 1895 and shortly after that Henri Becquerel observed radioactive behavior while