Nuclear Chemistry

1. Nuclear Chemistry

2. Remember when we ionize… • The ELECTRONS only get moved to change the charge on an atom. • WHY don’t the PROTONS move when we ionize?

3. When we change the number of protons, we change the element completely into another element!

4. Isotopes • Same element • Same number of protons • Same atomic number • Same number of electrons • Different number of neutrons • Different mass number

5. Isotope short-hand …it is referred to as “Carbon 12” Mass number 12 C 6 Atomic number Atomic symbol So how many neutrons in this carbon?

6. And this? 14 C 6 …is called “Carbon 14” There are 2 extra neutrons

7. A note about Atomic Mass… • atomic mass listed on the periodic table is the weighted average of mass of all the isotopes of an atom.

8. Stability • of isotopes is based on the ratio of the neutrons and protons in the atoms’ nucleus. • although most nuclei are stable, some are unstable and spontaneously decay emitting radiation

9. Transmutation • when the nucleus of an atom that converts it from one element to another • i.e. we change the PROTONS • can occur naturally or can be induced by the bombardment of the nucleus by high-energy particles. • since the # of protons (atomic #) determines the atom, we CHANGE THE ELEMENT COMPLETELY.

10. Nuclear Reactions • include • naturaltransmutation • artificial transmutation, • fission, and • fusion.

11. Natural Transmutation • describes nuclear changes due to natural radioactivity without any human intervention. • Example: Radioactive Carbon-14 will decay to stable Nitrogen- 14 without any assistance.

13. Artificial Transmutation • An artificially induced nuclear rxncaused by the bombardment of a nucleus with subatomic particles (usually neutrons) or small nuclei (Hydrogen or Helium). • In 1919 Ernest Rutherford bombarded nitrogen with alpha particles and converted it to hydrogen and oxygen, thus producing the first artificial transmutation of elements.

14. Rate of Decay • Some radioactive atoms decay at a faster rate than others. • The rate of decay is a chemical property of the atom and cannot be changed.

15. Drag Out Your Reference tables

16. Half-Lives • Because it takes so long for all of an isotope to decay, scientists use the length of time it takes for one-half of the original amount to decay. • This period is called the half life. • •Half life – the time required for one half the mass of a radioactive sample to decay.

17. Half-Life Graph

18. Nothing changes Half Life • The rate of decay for a radioactive sample is a set property of the sample. • What happens to the half-life of a sample when you; • Increase the Temperature? • Nothing changes half-life • Decrease the Temperature? • Nothing changes half-life • Increase the Surface Area? (i.e. grind it up) • Nothing changes half-life • Increase the Pressure? • Nothing changes half-life

19. Nuclear Chemistry Part II

20. Types of Decay • Alpha Decay emits an alpha particle. • The new atom's atomic number is lowered by two and its atomic mass number is reduced by four.

21. Types of Decay • Beta Decay emission of electrons from the nucleus • The new atom's atomic number is raised by one and its atomic mass stays the same.

22. Types of Decay • Positron Decay is the similar to Beta Decay except the particle released has a positive charge • The new atom's atomic number is lowered by one and its atomic mass stays the same.

23. Types of Decay • Gamma Decay is the release of stored energy from the nucleus. • No transmutation occurs. • gamma decay often occurs with alpha and beta negative decay in a disintegration series.

27. Nuclear Energy • Energy released in a nuclear reaction (fission or fusion) comes from the fractional amount of mass converted into energy. • Nuclear changes convert matter into energy. • From Einstein E=mC2 • Energy released during nuclear reactions is much greater than the energy released during chemical reactions. • There are benefits and risks associated with fission and fusion reactions.

28. Fission Rxns • occur when a large nucleus splits into two or more smaller nuclei plus some by-products. • By-products include free neutrons and photons (usually gamma rays). • Fission releases substantial amounts of energy

29. Fusion • Two or more smaller nuclei merge to form a larger nucleus, lots of energy and some by-products • Nuclei of two isotopes of hydrogen, deuterium (D) and tritium (T) react to produce a Helium (He) nucleus and a neutron (n).

30. Uses of Radioisotopes • used in medicine • industrial chemistry • radioactive dating • tracing chemical and biological processes • industrial measurement • nuclear power, • detection and treatment of diseases.

31. Geology Uses • Radiometric dating- a process in which scientists attempt to determine the ratio of parent nuclei to daughter nuclei within a given sample of a rock or fossil. • This ratio is then used to determine the absolute age of the rock or fossil. • C-14 to C-12 ratio in dating organic things • U-238 to Pb-206 ratio in dating crustal rocks

32. Risks • There are inherent risks associated with radioactivity and the use of radioactive isotopes. • Risks can include biological exposure, long-term storage and disposal, and nuclear accidents.

33. Biological exposure • All radiation can cause damage to organisms. • Most long-term damage is caused by the ionization of the atoms that make up the molecules in DNA. • If the damaged DNA are found in egg or sperm cells, the effects may be passed on for many generations (mutations)

34. Long-term storage and disposal • Fission reactions in produce radioactive wastes. • The wastes may have very long half-lives which make it difficult to dispose of them. • Some solids and liquids need to be encased in special containers and permanently stored underground. • Other materials are held until there radioactivity has lessened and are then diluted with other materials and released back into the environment.

35. Nuclear accidents • An example of nuclear accident might be one in which a reactor core is damaged such as Three Mile Island (near Harrisburg PA) or Chernobyl, Ukraine and Fukishima, Japan. • radiography accident where a worker drops the source into a river or sticks it in his pocket. • Due to government and business secrecy, it is difficult to determine with certainty the extent of some events.

36. 2012’s Questions (handout)

37. 82 [1] Allow 1 credit. Acceptable responses include, but are not limited to: • The nuclides used for fusion have smaller atomic masses than nuclides used for fission. • The nuclides used in fission are many times more massive. • Fusion particles are lighter.

38. 83 [1] Allow 1 credit for the correct number of protons and the correct number of neutrons for both • hydrogen nuclides. • Example of a 1-credit response:

39. 84 [1] Allow 1 credit for

40. 85 [1] Allow 1 credit. Acceptable responses include, but are not limited to: • Fusion produces more energy per gram of reactant. • The fusion process produces less radioactive waste. • The fusion reactant material is more readily available.