Chapter 4 Notes, part IV Nuclear Reactions:  Decay

Radioactivity & Decay Nuclear Chemistry deals with changes in the nucleus of atoms. Nuclear Chemistry deals with changes in the nucleus of atoms. Nuclear Reactions: rxns in which one element changes into another element (the # of p+ changes)Nuclear Reactions: rxns in which one element changes into another element (the # of p+ changes) Sometimes the nucleus of an atom is unstable and small parts break off releasing rays and particles called nuclear radiation.Sometimes the nucleus of an atom is unstable and small parts break off releasing rays and particles called nuclear radiation. Radioactive decay is the spontaneous process of an unstable nuclei losing energy by emitting radiationRadioactive decay is the spontaneous process of an unstable nuclei losing energy by emitting radiation

Radioactive Emissions 3 types of emissions - Alpha, Beta, Gamma Rays 3 types of emissions - Alpha, Beta, Gamma Rays

Radioactive Emissions Alpha Radiation Alpha Radiation Reflects toward negatively charged platesReflects toward negatively charged plates Alpha Particles (  Alpha Particles (    2 p + and 2 n 0 stuck together  same as the nucleus of a Helium atom. He42 +2  largest radioactive particle  will cause major damage.  least penetrating  can be stopped by a few cm of air.

Beta Radiation Reflects toward positively charged plates Reflects toward positively charged plates Beta Particles (   Beta Particles (    beta decay changes a n 0 into a p + and an e -. atomic # increases by 1 but mass does not change  atomic # increases by 1 but mass does not change neutron neutron proton proton electron electron (decay) (decay) (stays in nucleus) (stays in nucleus)  same as electron... e 0  more penetrating but less damaging than alpha Radioactive Emissions

Gamma Radiation No electrical charge so particles do not deflect toward either a positively or negatively charged plate No electrical charge so particles do not deflect toward either a positively or negatively charged plate Gamma Rays (  ) No mass, no charge, most penetratingNo mass, no charge, most penetrating Releases a metastable nuclei (m)Releases a metastable nuclei (m) Excited nuclei that just experiences  or  decayExcited nuclei that just experiences  or  decay 0 0

TYPE TYPE SYMBOL SYMBOL ATOMIC # CHANGE ATOMIC # CHANGE NEUTRON CHANGE NEUTRON CHANGE MASS CHANGE MASS CHANGE ALPHA (  ) ALPHA (  ) BETA (  ) BETA (  ) GAMMA (  ) by 2 by 2 He42 +2 by 4 by 4 e 0 by 1 by 1 no change no change  0 0 Radioactive Emissions

Practice: Practice: Pb Bi e 0 beta Th Th 230  0 gamma Ra Rn He 4 alpha 0 2 Radioactive Emissions

Fission vs. Fusion Nuclear Fission: The splitting of a nucleus into 2 smaller pieces Nuclear Fission: The splitting of a nucleus into 2 smaller pieces  releases a LOT of energy (10 6 times > any chem. rxn)  U-235 is the only naturally occurring isotope to undergo fission.  energy is most commonly converted to electricity. caused by a n 0 caused by a n 0

Each fission rxn. releases n 0 that cause other fission rxns Each fission rxn. releases n 0 that cause other fission rxns This causes a chain rxn that continues until there are This causes a chain rxn that continues until there are no more nuclei to split. Fission vs. Fusion

Nuclear Fusion: 2 or more nuclei are fused (combined) together to form a new, larger nucleus. Nuclear Fusion: 2 or more nuclei are fused (combined) together to form a new, larger nucleus.  releases much more energy than fission (E = mc 2 )  powers the sun (4 H atoms fuse to form a He atom)  requires extreme high temperatures and pressures Fission vs. Fusion

Nuclear Reactors Uses energy from fission to produce electricity. Uses energy from fission to produce electricity. Nuclear reactor in Baytown, TX Nuclear reactor in Baytown, TX

Radioactive Waste Fission rxns in reactors produce highly radioactive Fission rxns in reactors produce highly radioactiveby-products. ‘spent’ fuel cells are still highly dangerous and need to ‘spent’ fuel cells are still highly dangerous and need to be stored carefully. two major problems… two major problems…  long half-lives  very expensive two storage methods… two storage methods…  bottom of 12 meter deep pools  bury far beneath the earth’s surface U.S. produces ~ 3000 tons of waste / year. U.S. produces ~ 3000 tons of waste / year.

Radioisotopes in Medicine Tracers: Tracers: Radioisotope w/ short ½-life that is placed inside the body.  locates abnormalities in body functions  Ex… Iodine – 131, Technetium - 99 Other uses: Other uses:  agriculture (i.e. effectiveness of fertilizer)  radioactive labeling (i.e. oil companies)

Irradiation: Irradiation: hit w/ radiation from an outside source.  cancer treatments  X-rays  laser surgeries  MRI Other uses: Other uses:  food preservation  sterilization Radioisotopes in Medicine