1. Chapter 25Nuclear Chemistry!!! Boom, goes the nucleus Herriman High Chemistry

2. 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 Herriman High Chemistry

3. Radioisotopes • Radioisotopes are unstable 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. Herriman High Chemistry

4. 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. Herriman High Chemistry

5. Three types of Radioactivity Alpha – α – is the nucleus of a helium atom Can be stopped by a sheet of paper, is harmful only if ingested Beta – β – emission of an electron or positron Can be stopped by a sheet of lead, is harmful to all living tissue Gamma – γ – emission of a high energy photon Cannot be completely stopped. Very harmful to all living tissue. Radioactivity Herriman High Chemistry

6. Nuclear Reactions • Alpha Decay • Beta Decay • Gamma Emission Herriman High Chemistry

7. 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 Herriman High Chemistry

8. 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. Herriman High Chemistry

9. 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 ver, 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. Herriman High Chemistry

10. 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. Herriman High Chemistry

11. 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 Herriman High Chemistry

12. Radioactive Half Life • By definition, the amount of radioactive material that decays to another material is determined by its half life. • A half life is the amount of time required for ½ of the sample to decay. • The equation for a half life is: Where a0 is the amount you start with and a is the amount you have left after x half lives. Herriman High Chemistry

13. Sample Problem If a 20 gram sample of uranium -238 with a half live of 10 hours is allowed to decay for 3 days, how much will remain at the end of that time? Herriman High Chemistry

14. Solution Herriman High Chemistry

15. When a nucleus emits an alpha or a beta particle it becomes a new element – this process is called transmutation. This can occur naturally or artifically. This process can be useful for dating objects, or a a tracer in medical procedures. Transmutation of Elements Herriman High Chemistry