NUCLEAR CHEMISTRY!!! Boom, goes the nucleus RADIATION • Radiation is penetrating rays and/or particles released by a radioactive source. • A good example of radiation is UV rays from the sun. • As you know, these uv rays penetrate your skin to tan, burn, or even cause cells to malfunction and produce cancer cells RADIOISOTOPES • Radioisotopes are isotopes that have an unstable nucleus and, thus, undergo radioactive decay. • The reason a nucleus would be unstable is because it either does not have enough neutrons or has too many. • A nucleus has protons in it. If they were there by themselves, then what would happen? • So neutrons are kind of the glue holding all those protons together. • If there is not the correct ratio of protons to neutrons, then the nucleus will be unstable. RADIOACTIVE DECAY • An unstable nucleus will cause an atom of an element to decay, or fall apart, and form new elements. • For instance Carbon-14 falls apart or decays to form Nitrogen-14. • These unstable radioisotopes fall apart at a uniform (consistent) rate measured in half-lives. • Scientists can use the half-lives to figure out the age of substances containing these unstable radioisotopes. HALF- LIVES • A half life is the amount of time it takes for a substance to decay half way. • So the substance loses half of what it has each half life. This is easier understood by seeing it. Half lives Amount of substance Beginning amount 96 grams After 1st half life 48 grams After 2nd half life 24 grams After 3rd half life 12 grams After 4th half life 6 grams • Different substances have different half-lives: • Carbon-14 = 5730 years • Uranium-235 = 703.8 million years • Iodine-131 = 8 days HALF LIVE PROBLEMS • A substance has a half-life of 30 years: • If we started with 32 grams and now only have 2 grams left, how old is the substance? • 32/2= 16 16/2=8 8/2=4 4/2=2, so that’s four half lives • 4 half-lives x 30 years = 120 years • If we start with 96 grams, how many grams are left after 210 years? • 210 years/30 years in a half-life = 7 half-lives • 96/2=48 48/2=24 24/2=12 12/2=6 6/2=3 3/2=1.5 1.5/2=0.75g MORE HALF-LIFE PROBLEMS • What is the half-life of H2O2? • You start at about 230, so half is 115. Draw a line straight to the surve from 115. • Draw a line straight down from where you hit the curve, and that will tell you the half life. • In this case, the half-life is about 27 seconds. MORE HALF-LIFE PROBLEMS • If 20% of the original H2O2 remains, how much time has gone by? • You start at about 230, so 20% is 46. Draw a line straight to the curve from 46. • Draw a line straight down from where you hit the curve, and that will tell you how much time has gone by. • In this case, the time gone by is about 60 seconds. ALPHA PARTICLES • Alpha particles are released from radioactive nuclei. • The alpha particle is identical to a helium atom nucleus, having two protons and two neutrons • The alpha particle can be symbolized by the greek letter alpha: α • Or it can be symbolized by the notation for a helium nucleus: • Alpha particles have comparatively little energy and cannot even penetrate a piece of paper BETA PARTICLES • Beta particles result from breaking apart neutrons in an atom. • Beta particles are electrons released when a neutron breaks apart. The beta particle (electron) escapes while the other part of the neutron now forms a proton that stays in the nucleus • Beta particles can be symbolized by an electron: • Or they can be symbolized with the greek letter beta: • Beta particles (electrons) are much smaller than alpha particles so they can penetrate further with higher energy, but can still be stopped by aluminum foil or wood. GAMMA RAYS • Gamma rays are often released during radioactive decay. • Gamma rays have no mass: They are pure energy. • Though we say mass is conserved in nuclear reactions, on a very, very, very, very small scale some mass is lost. • This very small amount of mass is converted into energy. • Ever seen this before? • E = mc2 • The very small mass “lost” is converted into lots of energy in the form of gamma rays. • The symbol for gamma rays is the greek letter gamma: ϒ • Gamma rays are extremely high energy and can penetrate most anything. ATOMIC REACTIONS • Nuclear bomb video • And another STRONG NUCLEAR FORCE • This is the force, helped by the neutrons, that is holding the nucleus together • Remember that the protons are repelled by each other due to them all being positively charged. • The strong nuclear force is stronger than the repelling force so it holds the nucleus together. BAND OF STABILITY • If an isotope falls in the band of stability. • It has the correct ratio of neutrons to protons • And its nucleus is stable. • If an isotope falls outside of the band of stability • It has a “bad” ratio of neutrons to protons • And its nucleus is unstable NUCLEAR FISSION • Fission is when the nucleus of an atom is split apart • Fission is the type of nuclear reaction used in nuclear energy plants. • When the atom is split, some mass is ”lost” and … remember Einstein??? • The “lost” mass is actually converted into energy. NUCLEAR FUSION • Nuclear fusion happens when the nuclei of atoms combine (fuse) • In fusion, some of the mass is “lost” when the nuclei join together. • So, remember Einstein again? The “lost” mass is converted into energy. • All of the other elements in the universe are a result of hydrogen undergoing fusion in stars and producing helium. FUSION AND (SIMPLIFIED) ELEMENT MAKING • Fusion occurs inside stars • 4 Hydrogen atoms fuse in order to produce helium and gamma rays • 3 Helium atoms fuse in order to produce carbon atoms. Fusion in stellar cores • A carbon atom fuses to a helium atom in order to make oxygen. • This goes on until iron is formed. • The elements larger than iron are formed when stars explode (supernovas). Fusion in supernova explosions