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Nuclear Chemistry. Unit 2.5. Introduction to Nuclear Chemistry. Nuclear chemistry is the study of the structure of and the they undergo. atomi c nuclei. changes. Chemical vs. Nuclear Reactions.
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Nuclear Chemistry Unit 2.5
Introduction to Nuclear Chemistry • Nuclear chemistry is the study of the structure of and the they undergo. atomic nuclei changes
The Discovery of Radioactivity (1895 – 1898): Roentgen • found that invisible rays were emitted when electrons hit the surface of a fluorosent screen (discovered x-rays) • Becquerel accidently discovered that phosphorescent rock produced spots on photographic plates uranium
The Discovery of Radioactivity (1895 – 1898): Marie and Pierre Curie • isolated the components ( atoms) emitting the rays • – process by which atoms give off • – the penetrating rays and particles by a radioactive source uranium Radioactivity rays or particles Radiation emitted
The Discovery of Radioactivity (1895 – 1898): • identified 2 new elements, and on the basis of their radioactivity • These findings Dalton’s theory of indivisible atoms. Marie Curie, continued polonium radium contradicted
The Discovery of Radioactivity (1895 – 1898): Isotopes • – atoms of the same element with different numbers of • – isotopes of atoms with unstable nuclei (too many or too few neutrons) • – when unstable nuclei lose energy by emitting to become more neutrons Radioisotopes Radioactive decay radiation stable Spontaneous Reaction!
Alpha radiation • Composition – Alpha particles, same as helium nuclei • Symbol – Helium nuclei, He, α • Charge – 2+ • Mass (amu) – 4 • Approximate energy – 5 MeV • Penetrating power – low (0.05 mm body tissue) • Shielding – paper, clothing 4 2
Beta radiation • Composition – Beta particles, same as an electron • Symbol – e-, 0-1β • Charge – 1- • Mass (amu) – 1/1837 (practically 0) • Approximate energy – 0.05 – 1 MeV • Penetrating power – moderate (4 mm body tissue) • Shielding – metal foil
Gamma radiation • Composition – High-energy electromagnetic radiation • Symbol – ooγ • Charge – 0 • Mass (amu) – 0 • Approximate energy – 1 MeV • Penetrating power – high (penetrates body easily) • Shielding – lead, concrete
Chemical Symbols A chemical symbol looks like… p+ = e- = atomic # To find the number of , subtract the from the mass # 14 C atomic # 6 neutrons mass # atomic #
Nuclear Stability not • Isotope is completely stable if the nucleus will spontaneously . • Elements with atomic #s to are . • ratio of protons:neutrons ( ) • Example: Carbon – 12 has protons and neutrons decompose 1 20 very stable p+:n0 1:1 6 6
Nuclear Stability 21 83 • Elements with atomic #s to are . • ratio of protons:neutrons (p+ : n0) • Example: Mercury – 200 has protons and neutrons marginally stable 1:1.5 80 120
Nuclear Stability unstable > 83 • Elements with atomic #s are and . • Examples: and radioactive Uranium Plutonium
Alpha Decay α • Alpha decay – emission of an alpha particle ( ), denoted by the symbol , because an α has 2 protons and 2 neutrons, just like the He nucleus. Charge is because of the 2 . • Alpha decay causes the number to decrease by and the number to decrease by . • determines the element. All nuclear equations are . He 4 2 protons +2 mass 4 atomic 2 Atomic number balanced
Alpha Decay • Example 1: Write the nuclear equation for the radioactive decay of polonium – 210 by alpha emission. Step 4: Determine the other product (ensuring everything is balanced). Step 3: Write the alpha particle. Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 210 4 206 He Po Pb 84 2 82 Atomic #
Alpha Decay • Example 2: Write the nuclear equation for the radioactive decay of radium – 226 by alpha emission. Step 4: Determine the other product (ensuring everything is balanced). Step 3: Write the alpha particle. Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 226 4 222 He Ra Rn 88 2 86 Atomic #
Beta decay β • Beta decay – emission of a beta particle ( ), a fast moving , denoted by the symbol or . β has insignificant mass ( ) and the charge is because it’s an . • Beta decay causes change in number and causes the number to increase by . • A neutron is converted to a proton and a beta particle. electron e- e 0 0 -1 electron -1 no mass atomic 1
Beta Decay • Example 1: Write the nuclear equation for the radioactive decay of carbon – 14 by beta emission. Step 4: Determine the other product (ensuring everything is balanced). Step 3: Write the beta particle. Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # e 14 0 14 C N -1 6 7 Atomic #
Beta Decay • Example 2: Write the nuclear equation for the radioactive decay of zirconium – 97 by beta decay. Step 4: Determine the other product (ensuring everything is balanced). Step 3: Write the beta particle. Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # e 0 97 97 Zr Nb -1 40 41 Atomic #
Gamma decay electromagnetic • Gamma rays – high-energy radiation, denoted by the symbol . • γ has no mass ( ) and no charge ( ). Thus, it causes change in or numbers. Gamma rays almost accompany alpha and beta radiation. However, since there is effect on mass number or atomic number, they are usually from nuclear equations. γ 0 0 no mass atomic always no omitted
Transmutation Transmutation the of an atom of one element to an atom of a different element. Radioactive decay is one way that this occurs! conversion
Review 4 2 0 -1
Half-Life half Half-life time • is the required for of a radioisotope’s nuclei to decay into its products. • For any radioisotope,
Half-Life • For example, suppose you have 10.0 grams of strontium – 90, which has a half life of 29 years. How much will be remaining after x number of years? • You can use a table:
Half-Life • Or an equation! initial mass mt = m0 x (0.5)n mass remaining # of half-lives
Half-Life • Example 1: If gallium – 68 has a half-life of 68.3 minutes, how much of a 160.0 mg sample is left after 1 half life? ________ 2 half lives? __________ 3 half lives? __________
Half-Life • Example 2: Cobalt – 60, with a half-life of 5 years, is used in cancer radiation treatments. If a hospital purchases a supply of 30.0 g, how much would be left after 15 years? ______________
Half-Life • Example 3: Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days? ______________
Half-Life • Example 4: The half-life of polonium-218 is 3.0 minutes. If you start with 20.0 g, how long will it take before only 1.25 g remains? ______________
Half-Life • Example 5: A sample initially contains 150.0 mg of radon-222. After 11.4 days, the sample contains 18.75 mg of radon-222. Calculate the half-life.
Nuclear Reactions • Characteristics: • Isotopes of one element are into isotopes of another element • Contents of the change • amounts of are released changed nucleus energy Large
Types of Nuclear Reactions • decay – alpha and beta particles and gamma ray emission • Nuclear - emission of a or Radioactive disintegration proton neutron
Nuclear Fission Fission splitting • - of a nucleus • - Very heavy nucleus is split into approximately fragments • - reaction releases several neutrons which more nuclei • - If controlled, energy is released (like in ) Reaction control depends on reducing the of the neutrons (increases the reaction rate) and extra neutrons ( creases the reaction rate). two equal Chain split slowly nuclear reactors speed absorbing de
Nuclear Fission • - 1st controlled nuclear reaction in December 1942. 1st uncontrolled nuclear explosion occurred July 1945. • - Examples – atomic bomb, current nuclear power plants
Nuclear Fission • Disadvantages • Produces high level radioactive waste that must be stored for 10,000’s of years. • Meltdown causes disasters like in Japan and Chernobyl. • Advantages • Zero air pollution • Not a fossil fuel so doesn’t contribute to climate change
Nuclear Fusion • - Fusion: Combining of two nuclei • - Two light nuclei combine to form a single heavier nucleus • - Does not occur under standard conditions (positive nuclei repel each other) • - Advantages compared to fission – No radioactive waste, inexpensive , • - Disadvantages - requires large amount of energy to start, difficult to control. • - Examples – energy output of stars, hydrogen bomb, future nuclear power plants
Uses of Radiation • Radioactive dating: Carbon–14 used to determine the age of an object that was once alive. • Detection of diseases: Iodine–131 used to detect thyroid problems, technetium–99 used to detect cancerous tumors and brain disorders, phosphorus – 32 used to detect stomach cancer. • Treatment of some malignant tumors (cobalt–60 and cesium–137) cancer cells are more sensitive to radiation than normal, healthy cells
Uses of Radiation • X-rays • Radioactive tracers: used in research to tag chemicals to follow in living organisms • Everyday items: thorium–232 used in lantern mantels, plutonium–238 used in long-lasting batteries for space, and americium–241 in smoke detectors.