Nuclear Chemistry

Aim: What is radioactivity and how do nuclear reactions differ from chemical reactions? Learning Objectives: Students should understand what causes an isotope to be radioactive, which elements are radioactive and that the process of radioactivity changes the element. Students should be able to recognize the symbols of radiation particles. Students should be able to distinguish nuclear reactions from other reactions and be able to identify the type of nuclear reaction. Students should be able to determine the missing particle in an incomplete nuclear reaction.

Introduction The ratio of protons to neutrons determines the stability of an isotope. 1:1 ratio = stable. All elements above 83 are unstable and thus all of their isotopes are radioactive. Nearly every element below 83 has at least one radioactive isotope (called radioisotope). Radioactive isotopes “decay” (change) into other elements by losing particles and energy. When particles are lost from the nucleus it results in one element becoming another. This is called transmutation.

Which isotope is radioactive? The three isotopes of hydrogen. Note the nucleons.

Some Common Forms of Radiation Missing information can be found on Table O of the Reference Tables. Particle Mass Charge Notation and Symbol Penetrating Power Alpha Low, cannot pass through paper Beta Moderate, cannot pass though skin Positron Moderate, cannot pass through skin Gamma High, can pass into body, blocked by lead

Which particle is which?

Notation Atomic# Mass Neutrons

TYPES OF NUCLEAR REACTIONS

Natural Transmutation (Look for only one reactant) Alpha Decay: alpha particle in the products Beta Decay: beta particle in the products Positron Emission: positron in the products

Alpha Decay Natural Transmutation (Spontaneous)

Beta Decay Natural Transmutation (Spontaneous)

Positron Emission Natural Transmutation (Spontaneous)

HW: Pages 219-220 Q 1-15

Artificial Transmutation An alpha particle, neutron or proton is combined with an atom to make a heavier atom.

Artificial Transmutation Distinguish artificial transmutation from natural transmutation by looking for alpha particles, protons or neutrons on the reactant side. The bombarding particle (alpha, beta or neutron) combines with the nucleus and makes one heavier atom.

Fission Used in nuclear bombs, a heavy nucleus is split by being bombarded with a neutron.

Fission Splitting of a heavy nucleus to produce lighter nuclei. Distinguish from artificial transmutation by looking for multiple atoms on the product side.

Occurs on the sun, hydrogen atoms fuse to form helium atoms. Fusion Occurs on the sun, hydrogen atoms fuse to form helium atoms.

Fusion Combining light nuclei to make heavier nuclei. http://antwrp.gsfc.nasa.gov/apod/ap051106.html

E=mc2 Fission and fusion both result in some loss of matter. Meaning the mass of the products is slightly less than the mass of the reactants. What law is being broken? How is that possible? Why might fusion reactions be a better energy source that fission reactions?

Identify the following reactions

Applying Conservation of Mass and Charge to find the missing particle.

HW: Page 221 Q 16-23 Page 223 Q 24-33

Aim: What can we learn from radioactive elements? Learning Objectives: Students should be able to calculate the fraction of a radioactive sample remaining by using the isotopes’ half-life value. Students should be able to determine the mass of a remaining radioactive sample by using half-life. Students should be able to determine the mass of the original radioactive sample by using half-life. Students should be able to determine half-life from a graph. Students should know the uses of specific radioisotopes and the dangers/drawbacks of using radiation.

Half-Life Table N Definition: The amount of time it takes for half of a sample of a radioactive substance to decay.

What is the half-life of this element?

Using Table N to Determine Radioactive Decay Question Types: What fraction of a sample remains? Which isotope on Table N will have only 1/16 of it’s original mass after 28.8 seconds? 2. How much mass remains? How much of an 80 gram sample of Radium-226 will be remaining after 8,000 years? What was the mass of the original sample? If 3.0 grams of Sr-90 in a rock sample remained in 1999, approximately how many grams of Sr-90 were present in original rock samples of 1943?

Applications Medicine: radiolabeling (short half-lives) Energy: nuclear reactor History/Science: radio dating (i.e. carbon dating, uranium dating) (longer half-lives) HW: Read Pages 226-228, Uses and Dangers of Radioisotopes and answer questions on posted worksheet.

HW: Pages 225-226 Q 34-47 Page 228 Q 48-57 CHAPTER QUESTIONS Pages 229-232 Q 1-53

Practice