Nuclear Chemistry Unit 16

Introduction to Nuclear Chemistry Nuclear chemistry is the study of the structure of and the they undergo. atomic nuclei changes

Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays

Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element

Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons

Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons Associated with small energy changes Associated with large energy changes

Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons Associated with small energy changes Associated with large energy changes Reaction rate influenced by temperature, particle size, concentration, etc. Reaction rate is not influenced by temperature, particle size, concentration, etc.

The Discovery of Radioactivity (1895 – 1898): Roentgen found that invisible rays were emitted when electrons bombarded the surface of certain materials. Becquerel accidently discovered that phosphorescent salts produced spontaneous emissions that darkened photographic plates uranium

The Discovery of Radioactivity (1895 – 1898): Marie Curie isolated the components ( atoms) emitting the rays – process by which particles give off – the penetrating rays and particles by a radioactive source uranium Radioactivity rays Radiation emitted

The Discovery of Radioactivity (1895 – 1898): polonium identified 2 new elements, and on the basis of their radioactivity These findings Dalton’s theory of indivisible atoms. radium contradicted

The Discovery of Radioactivity (1895 – 1898): same Isotopes – atoms of the element with different numbers of – isotopes of atoms with nuclei (too / neutrons) – when unstable nuclei energy by emitting to attain more atomic configurations ( process) neutrons Radioisotopes unstable many few Radioactive decay radiation lose stable spontaneous

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-, β 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 – γ Charge – 0 Mass (amu) – 0 Approximate energy – 1 MeV Penetrating power – high (penetrates body easily) Shielding – lead, concrete

Review of Atomic Structure Nucleus Electrons 99.9% of the mass 1/10,000 the size of the atom 0.01% of the mass

Review of Atomic Structure Nucleus Electrons 99.9% of the mass 1/10,000 the size of the atom 0.01% of the mass Composed of protons (p+) and neutrons (n0) Composed of electrons (e-)

Review of Atomic Structure Nucleus Electrons 99.9% of the mass 1/10,000 the size of the atom 0.01% of the mass Composed of protons (p+) and neutrons (n0) Composed of electrons (e-) Positively charged Negatively charged

Review of Atomic Structure Nucleus Electrons 99.9% of the mass 1/10,000 the size of the atom 0.01% of the mass Composed of protons (p+) and neutrons (n0) Composed of electrons (e-) Positively charged Negatively charged Strong nuclear force (holds the nucleus together) Weak electrostatic force (because they are charged negatively

mass # atomic # neutrons atomic # mass # Chemical Symbols A chemical symbol looks like… To find the number of , subtract the from the mass # 14 C atomic # 6 neutrons atomic # mass #

not decompose 1 20 very stable 1:1 p+:n0 6 6 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 1:1 p+:n0 6 6

21 82 marginally stable 1:1.5 80 120 Nuclear Stability 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

> 82 unstable radioactive Uranium Plutonium Nuclear Stability > 82 unstable Elements with atomic #s are and . Examples: and radioactive Uranium Plutonium

α He protons +2 mass 4 atomic 2 Atomic number balanced 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 3: Write the alpha particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 210 Po 84 206 Pb 4 He 2 82 Atomic #

Alpha Decay Example 2: Write the nuclear equation for the radioactive decay of radium – 226 by alpha emission. Step 3: Write the alpha particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 226 Ra 88 222 Rn 4 He 2 86 Atomic #

β electron e- e -1 electron no mass atomic 1 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 . electron e- e -1 electron -1 no mass atomic 1

C e N Beta Decay 14 6 14 -1 7 Step 3: Write the beta particle. Example 1: Write the nuclear equation for the radioactive decay of carbon – 14 by beta emission. Step 3: Write the beta particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 14 C 6 14 e -1 N 7 Atomic #

Zr e Nb Beta Decay 97 40 97 -1 41 Step 3: Write the beta particle. Example 2: Write the nuclear equation for the radioactive decay of zirconium – 97 by beta decay. Step 3: Write the beta particle. Step 4: Determine the other product (ensuring everything is balanced). Step 2: Draw the arrow. Step 1: Write the element that you are starting with. Mass # 97 Zr 40 97 e -1 Nb 41 Atomic #

electromagnetic γ no mass atomic always no omitted Gamma decay 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 no mass atomic always no omitted

Transmutation conversion radioactive – the of one atom of one element to an atom of a different element ( decay is one way that this occurs!) conversion radioactive

Type of Radioactive Decay Review Type of Radioactive Decay Particle Emitted Change in Mass # Change in Atomic # Alpha α He -4 -2 Beta β e +1 Gamma γ 4 2 -1

half Half-life time Half-Life is the required for of a radioisotope’s nuclei to decay into its products. For any radioisotope, # of ½ lives % Remaining 100% 1 50% 2 25% 3 12.5% 4 6.25% 5 3.125% 6 1.5625%

Half-Life

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: # of ½ lives Time (Years) Amount Remaining (g) 10 1 29 5 2 58 2.5 3 87 1.25 4 116 0.625

initial mass mt = m0 x (0.5)n mass remaining # of half-lives 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.

changed nucleus Large energy Nuclear Reactions Characteristics: Isotopes of one element are into isotopes of another element Contents of the change amounts of are released changed nucleus Large energy

Types of Nuclear Reactions decay – alpha and beta particles and gamma ray emission Nuclear - emission of a or Radioactive disintegration proton neutron

Fission splitting two equal Chain split slowly nuclear reactors speed 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

Fusion combining light single + + no radioactive waste large start Nuclear Fusion Fusion combining - of a nuclei - Two nuclei combine to form a heavier nucleus - Does not occur under standard conditions ( repels ) - Advantages compared to fission - , - Disadvantages - requires amount of energy to , difficult to - Examples – energy output of stars, hydrogen bomb, future nuclear power plants light single + + inexpensive no radioactive waste large start control

Uses of Radiation Radioactive _______________ - Carbon - ____ used to determine the ________ of an object that was once alive. ___________________________ of diseases – Iodine – 131 used to detect _________________ problems, technetium – 99 used to detect ___________ tumors and ____________ disorders, phosphorus – 32 used to detect __________ cancer. Treatment of some _______________________ (cobalt – 60 and cesium – 137) – cancer cells are more ________________________ to radiation than normal, healthy cells

Uses of Radiation X-rays Radioactive ________________ (used in research to _______ chemicals) Everyday items – thorium – 232 used in ______________________, plutonium – 238 used in _______________________, and americium – 241 in ___________________________________