Nuclear Chemistry Chapter 28
Nuclear Reactions Reactions that occur in the NUCLEUS. Cannot be slowed down, speeded up, or turned off.
Chemical Reactions vs. Nuclear Reactions Chemical Rxns: Atoms gain stability by attaining stable electron configurations Nuclear Rxns: Unstable isotopes (radioisotopes) gain stability by making changes within their nuclei Not affected by pressure, temp., or catalysts
Radioactivity Radioisotopes are radioactive because they have unstable nuclei. Stability of the nucleus: Ratio of neutrons to protons Too many or few neutrons relative to the # of protons = unstable nucleus
Radioactive Decay The process in which an unstable nucleus loses energy by emitting radiation. Spontaneous process and doesn’t need any input of energy. Unstable radioisotopes are eventually transformed into stable (nonradioactive) isotopes of a different element.
3 Types of Radiation ALPHA () radiation—could be stopped by a sheet of paper +2 charge --helium atom 42He BETA () radiation—could be stopped by a sheet of aluminum -1 charge --high-speed electron
Types of Radiation (cont.) GAMMA () radiation—could be stopped by lead No charge --no mass
Ernest Rutherford He used uranium and thorium, and put them in a magnetic field Alpha and beta particles are deflected by a magnetic field. Gamma rays moved through the field without being affected.
Nuclear Stability Stable nuclei do not decay or change with time Stability depends on its neutron-to-proton ratio Out of the 1500 known nuclei, 264 of them are stable
Half-Life Half-life (t1/2): the time required for one-half of the atoms of a radioisotope to emit radiation and to decay to products
Example: Half-life Assume there are 2.00 g of N-13. How many grams of N-13 will exist after 3 half-lives? # of half-lives Mass of N-13 0 2.00 g 1 1.00 g 2 0.50 g 3 0.25 g
Uses For Radioisotopes C-14 Used to date fossils and artifacts Many artificially produced radioisotopes have very short half-lives Great advantage in nuclear medicine (Co, I) U-238 (half-life of 4.5 x 109 years) Used to date rocks as old as our solar system
Transmutation Reactions Transmutation: the conversion of an atom of one element to an atom of another element Some transmutations occur naturally through radioactive decay (, ) All other transmutations are artificially done in laboratories High-energy particles bombard the nucleus of an atom
Transuranium Elements Elements in the periodic table with atomic numbers above 92 None occur in nature and all are radioactive Synthesized in nuclear reactors and nuclear accelerators
Nuclear Fission and Fusion Fusion: Two nuclei combine to produce a nucleus of heavier mass. Fission: Splitting of a nucleus into smaller fragments. Nuclei of certain isotopes are bombarded with neutrons 9
Fission
Fission Produces a Chain Reaction
Nuclear Fission Enormous amounts of energy released 1 kg of U-235 releases an amount of energy equal to that generated in an explosion of 20,000 tons of dynamite Atomic bombs are devices that start uncontrolled nuclear chain reactions
Nuclear Fission (cont.) Fission can be controlled so that energy is released more slowly Nuclear reactors—heat removed from the reactant core by a coolant fluid (water) Control rods used to control neutron absorption
Nuclear Fusion Thermonuclear rxn Energy released from the sun Fusion rxns release more energy than fission rxns Takes place only at very high temperatures—in excess of 40,000,000C Fusion products usually not radioactive
Nuclear Fusion (cont.) Hydrogen Bomb Matter exists as a plasma High temps required to initiate fusion rxns Atomic bomb—used as a triggering device to set off the H-bomb Matter exists as a plasma