NUCLEAR CHEMISTRY

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

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

Chemical vs. Nuclear Reactions Chemical ReactionsNuclear Reactions Occur when bonds are brokenOccur 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 ReactionsNuclear Reactions Occur when bonds are brokenOccur 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 ReactionsNuclear Reactions Occur when bonds are brokenOccur 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 electronsMay involve protons, neutrons, and electrons Associated with small energy changes Associated with large energy changes

Chemical vs. Nuclear Reactions Chemical ReactionsNuclear Reactions Occur when bonds are brokenOccur 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 electronsMay involve protons, neutrons, and electrons Associated with small energy changesAssociated 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 uranium salts produced spontaneous emissions that darkened photographic plates

The Discovery of Radioactivity (1895 – 1898):  Marie Curie isolated the components (uranium atoms) emitting the rays  Identified 2 new elements, polonium and radium, on the basis of their radioactivity  These findings contradicted Dalton’s theory of indivisible atoms.  Radioactivity – process by which particles give off rays  Radiation – the penetrating rays and particles emitted by a radioactive source

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

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

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  Origin – neutron turned to a proton + 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

Beta + radiation  Composition – Beta particles, exact opposite of an electron, called a positron  Origin – proton turned to a neutron + positron  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

Nuclear Stability  Isotope is completely stable if the nucleus will not spontaneously decompose.  Elements with atomic #s 1 to 20 are very stable.  1:1 ratio of protons : neutrons (p + : n 0 )  Example: Carbon – 12 has 6 protons and 6 neutrons

Nuclear Stability  Elements with atomic #s 21 to 82 are marginally stable.  1:1.5 ratio of protons:neutrons (p + : n 0 )  Example: Mercury – 200 has 80 protons and 120 neutrons

Nuclear Stability  Elements with atomic #s >82 are unstable and radioactive.  Examples: Uranium-235 and plutonium-239

Alpha Decay  Alpha decay – emission of an alpha particle ( α ), denoted by the symbol  Alpha decay causes the mass # to decrease by 4 and the atomic # to decrease by 2.  Atomic # determines the element. All nuclear equations are balanced with respect to mass #s AND atomic #s. 4 2

Alpha Decay  Example 1: Write the nuclear equation for the radioactive decay of polonium – 210 by alpha emission. Step 1: Write the element that you are starting with. Mass # Atomic # Step 2: Draw the arrow.Step 3: Write the alpha particle.Step 4: Determine the other product (ensuring everything is balanced).

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

Beta - decay  Beta decay – emission of a beta particle ( β - ), a fast moving electron, denoted by the symbol e - or.  Beta decay causes no change in mass number and causes the atomic number to increase by 1. 0

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

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

Beta + decay  Beta+ decay – emission of a beta particle ( β + ), a fast moving positron, denoted by the symbol e + or.  Beta+ decay causes no change in mass number and causes the atomic number to decrease by

Beta + Decay  Example 1: Write the nuclear equation for the radioactive decay of calcium – 37 by positron emission. Step 1: Write the element that you are starting with. Mass # Atomic # Step 2: Draw the arrow.Step 3: Write the beta particle.Step 4: Determine the other product (ensuring everything is balanced).

Beta+ Decay  Example 2: Write the nuclear equation for the radioactive decay of potassium – 37 by beta+ decay. Step 1: Write the element that you are starting with. Mass # Atomic # Step 2: Draw the arrow.Step 3: Write the beta particle.Step 4: Determine the other product (ensuring everything is balanced).

Gamma decay  Gamma rays – high-energy electromagnetic radiation, denoted by the symbol γ.  γ has no mass (0) and no charge (0). Gamma rays almost always accompany alpha and beta radiation. However, since there is no effect on mass number or atomic number, they are usually omitted from nuclear equations.

Transmutation  Transmutation – the conversion of one atom of one element to an atom of a different element  Spontaneous radioactive decay is one way that this occurs (fission)  Nuclear fusion in the sun  Artificial transmutation by people with particle accelerators to create bigger atoms Typically involve neutrons ( n) as reactants or products 1 0

Review Type of Radioactive Decay Particle Emitted Change in Mass # Change in Atomic # Alpha α He -4-2 Beta - β - e 0+1 Beta + β + e 0 Gamma γ