Nuclear Chemistry

1. Nuclear Chemistry DHS Chemistry Chapters 4 and 25

2. Little House on the Prarie

3. Review: Structure of an Atom

4. Structure of an Atom • An atom consists of three types of subatomic particles, protons, neutrons, and electrons.

5. Structure of an Atom • ______ and _______ are located in the nucleus • Electrons are in a cloud surrounding the nucleus. • The number of protons is equal to the ____________. Protons neutrons atomic number

6. Structure of an Atom • If the atom is neutral, the number of electrons is equal to the number of ______. • The mass number is equal to number of protons + number of neutrons. protons Mass # = p+ + no

7. Structure of an Atom • Elements with the same number of protons, but have different numbers of neutrons is called an ______. isotope

8. Structure of an Atom

9. What’s a chemical reaction?

10. Chemical Reactions

11. Why Call it Nuclear Chemistry? See unitedstreaming.com

12. Chemical VS. Nuclear • Nuclear reactions are caused from unstable nuclei becoming stable throughradioactivedecay. • Releasing particles and high-energy waves • Alters the numberof nuclear particles (neutrons and protons). • Nuclear reactions are very different from chemical reactions.

13. Chemical Reactions 1. Occur when bonds are broken and formed. 2. Atoms remain unchanged, though they may be rearranged. 3. Involve only valence electrons. 4. Associated with small energy changes. 5. Reaction rate is influenced by temperature, pressure, concentration, and catalyst.

14. Nuclear Reactions 1.Occur when nuclei emit particles and/or rays. 2. Atoms are often converted into atoms of another element. Thus their identity changes. 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.

15. What is an isotope?

16. Isotope Examples Mass Numbers Atomic # = protons Lithium - 6 Lithium - 7

17. Isotopes • Isotopes are atoms of the same element that vary in their number of neutrons, thus they have different mass numbers. • The convention for writing isotope names is first the element name dash and then the mass number.

18. For example: Carbon-14, carbon-12 carbon-13 How many protons and neutrons does each of the isotopes of carbon have? • Carbon – 14 8 neutrons, 6 protons • Carbon – 12 6 neutrons, 6 protons • Carbon – 13 7 neutrons, 6 protons Mass Number (protons + neutrons)

19. More on Isotopes • When an isotope is unstable it is called a radioisotope. • To gain a more stable configuration, the nuclei emit radiation. • The resulting stable atom is called the daughter product. • This is called radioactive decay.

20. Strong Nuclear Force • The dense nucleus has two different kinds of nuclear particles (protons + neutrons) closed packed together. • The protons are positively charged nucleons. • The neutrons are neutral nucleons. • All of the protons in the nucleus repel each other and cause an electrostatic force that pushes the nucleus apart.

21. However, there is a force holding the nucleus together. • The strong nuclear force is a force that acts only on subatomicparticles that are extremely close together. • If the strong nuclear force overcomes the electrostatic force, the nucleus stays together.

22. Neutron to Proton Ratio • The strong nuclear force is not always strong enough to overcome the electrostatic force. When this happens the nucleus breaks apart. The stability of the nucleus can be determined by the ratio of neutrons to protons.(n/p)

23. Neutron to Proton Ratio • Elements with low atomic numbers are most stable when the neutron to proton ratio is 1:1. • As the atomic number increases, more and more neutrons are needed to overcome the electrostatic force. • Thus, the stable ratio of neutron to proton increases as the atomic number increases. • 1.5:1 is the largest ratio for a stable nucleus.

24. The Band of Stability • The graph above plots the neutrons versus protons. The band created is called the band of stability. Anything that falls outside of that band is radioactive. • All elements with an atomic number greater than 83 are radioactive.

25. Stable if: Smaller than Fe ~1 1 Between Fe & Pb 1-1.5 1 Bigger than Pb 1.5 1 Nuclear StabilityNeutron : Protons

26. Extra Practice • Calculate the neutron to proton ratio, and determine if the isotope is stable. 1. 2. U- 293 2:2  1:1 stable 201:92  2.18:1 unstable

27. Example: Determine the neutron to proton ratio for Lead-206. Is it stable? Lead – 206 82 protons 124 neutrons (206 – 82) 124 = 1.51 stable 82 1 ratio

28. III. Radioactivity

29. Geiger Counter

30. Radioactive Substances • Bananas • Atomic fire ball candies • Colored gemstones (blue topaz) • Fiesta Ware • Table ware that contained unsafe amounts of radioactive Uranium • Uranium for color glaze. Up to 14% can be Uranium

31. Types of Radiation

32. Types of Decay • Nuclear reactions change an atom of one element to an atom of another element. This process is called transmutation. In a nuclear reaction there are three common types of radiation that are emitted: alpha, beta, and gamma. The first two are involved in transmutation, changing the identity of the atom.

34. The experiment

35. Emit means to give off or release

36. Alpha Particles • Alpha particles contain the same composition as a helium nucleus. Out of all of the radiation particles, alpha particles move the slowest and are the least penetrating. As a result of alpha decay, the mass number decreases by 4 and the atomic number decreases by 2. or

37. Alpha decay

38. Beta Particles • Beta particles are similar to an electron except they come from the unstable nucleus of the atom. Beta particles are formed and ejected when a neutron decays to a proton and an electron. The proton stays in the nucleus and the electron is the beta particle. Beta emission is a constant flow of quick moving electrons that can be stopped by a metal foil. As a result of beta decay the atomic number increases by one. The mass number does not change.

40. Gamma Rays • Gamma rays are short wavelengths (photons) that move the quickest of all the types of decay, and the most harmful! They are very high-energy electromagnetic radiation. These rays often are released at the same time as an alpha or beta particle. The ray is the energy lost in the reaction. Gamma emission does not affect the atomic number or the mass number of the isotope.

41. Gamma Rays Are very dangerous!! (write that down)

42. C. Gamma ( ) Emission • usually occurs along with other forms of radiation. • Gamma particle is emitted • No change in mass number • No change in atomic number

44. Practice Problems 1. Why is radiation given off? 2. What is the most penetrating particle? 3. What is a main difference between a nuclear reaction and a chemical reaction? 4. Is Carbon-14 radioactive? Why or Why not?

45. III. Balancing Nuclear Reactions

46. Mass number Mass number Atomic number Atomic number Balancing Nuclear Reactions • In nuclear reaction equations we account for all of the changes in the mass number and atomic mass that occur through the decay of the nucleus. • To verify this, we include the mass number and atomic mass of every particle or atom involved in the reaction.

47. Solving Problems • When solving/balancing a nuclear reaction, • Look to find the difference of the mass numbers and atomic numbers between the reactants and the products. • This will indicate the particle that was released or the atom that was formed. • Make sure you have the sametotal mass number and atomic number on both sides of the equation.

48. Nuclear Equations

49. Nuclear Reactions

50. Practice Fill in the blank with the proper radiation particle or isotope 1) 2) 3) 4)