RADIOACTIVITY

RADIOACTIVITYRADIATIONRadiation are when high energy rays and particles are emitted from radioactive sourcesRadioactivity is the release of the high energy particles or raysNUCLEAR SYMBOLChemists represent certain elements using standard atomic notation The rounded mass number is on the left as a superscriptThe atomic number is written on the left as a subscript

Example: K39Atomic mass19Atomic NumberElementAtomic NumberRounded Atomic MassNuclear SymbolNeonSiliconLithiumBromineCarbonPhosphorus102020Ne10142828Si14377Li3358080Br3561212C6153131P54Whats the difference?Which one is heavier?What is the same?Group 1Group 2Group 3They are all the same color, but have DIFFERENT masses because there are a DIFFERENT number of blocks!Lets look at this....p+nIts HYDROGEN!!!

p+nnp+nnnStill hydrogen....Still hydrogen????Because hydrogens atomic number is 1 = 1 proton = 1 electronThese are all hydrogen.... But have different number of protons??

p+ISOTOPESIsotopes are elements with different number of neutronsIf they have a different number of neutrons, they have a different atomic mass!But, they still have the same number of protons and electronsp+np+nnp+nnnREPRESENTING ISOTOPESNuclear symbols are used to represent isotopesMass number = superscriptAtomic number = subscriptNaming isotopes only consists of the name atomic massExamples: potassium 40carbon - 14

MASS NUMBERMass number is a number that represents the total number of protons and neutrons in an atomMass number:Mass # = atomic # + # of neutronsNumber of neutrons:# of neutrons = mass # - atomic #Number of protons:# of protons = mass # - # of neutronsExamples of isotopes:IsotopeAtomic mass

(neutrons + number)Atomic number

(protons)Number of neutrons

(mass number)Nuclear symbolCarbon-14Atomic mass!!!!!146814C 6Example 2IsotopeAtomic mass

(neutrons + number)Atomic number

(protons)Number of neutrons

(mass number)Nuclear symbolAtomic mass!!!!!41192241K19Potassium -41Example 3IsotopeAtomic mass

(neutrons + number)Atomic number

(protons)Number of neutrons

(mass number)Nuclear symbol8358Li3Lithium - 8ISOTOPEMASS NUMBERATOMIC NUMBERNUMBER OF NEUTRONSNUCLEAR SYMBOLNEON -2121101121 Ne10SILICON -3030142630 Si14LITHIUM -77347 Li3Aluminum- 2727131427 Al13Lithium- 66336 Li3Carbon - 14146814 C6Magnesium -2525121325 Mg12Fluorine - 191991019 F9CHEMICAL REACTIONSChemical reactions occur because atoms DONT have a valence shell. Therefore, they are unstable!!! So they interact with each other by creating ionic bonds or covalent bondsBut ONLY the electron arrangements (configurations) change, NOT THE PROTONS OR NEUTRONS... Nuclear reactions are different...RADIOACTIVE DECAYRadioactive decay is the process in which the unstable nucleus (protons and neutrons) become stable by emitting radiationBy emitting radiation, the atom changes into another element.... Isotopes that are capable of radioactive decay are called radioisotopesERNEST RUTHERFORD

REVIEWNUCLEAR SYMBOLAtomic mass =Atomic number =Superscript up highSubscript down lowTHREE TYPES OF RADIATIONAlpha radiationStream of positive alpha particles emitted from the nucleusBeta RadiationStream of negative beta particles emitted from the nucleusGamma RadiationStream of neutral gamma particles emitted from the nucleus

Another Way to RememberALPHAPROTONBETAELECTRONALPHA RADIATIONA stream of alpha particles emitted from the nucleusAlpha particles are massive and positively chargedBecause their massive, they are slow moving and dont penetrate materials as muchAlpha particles are essentially the same as helium atomsSymbol:

ALPHA RADIATIONAn alpha particle is emitted in a process called alpha decay Then the atomic mass will decrease by 4The atomic number will decrease by 2And a new atom will be formed!

Another Example:201Hg 80197Pt + 784He2231Pa 91227Ac + 894He2Complete the following:

204Pb 82227Ac 89225Ac 89196Au 79211Fr 8723BETA RADIATIONBeta particle is an electron and is negatively chargedThey are light weightFast movingGreater penetrating powerSYMBOL

Electrical chargeAtomic MassBETA DECAYFirst a neutron changes into a proton and an electron

np+e-Then the proton remains in the nucleus while the electron shoots out with a lot of energy

np+e-e-The emission of this electron, or beta particle is called beta decay

Beta DecayIf a beta particle has been emittedThen the atomic mass will remain the sameBut, the atomic number will increase by 1And a new atom is formed!!Example:

Another Example24Na 1124 Mg + 12 0e-1201Hg 80201 Tl + 81 0e-1Complete the following:

14N 76Li 324Mg12201Au 6952Fe2642K19GAMMA RADIATIONGamma radiation consists of rays of high energy, short-wavelength radiation. The gamma particle emitted during gamma decay has no mass and no chargeGreatest penetrating powerSYMBOL

Gamma DecayGamma decay results from the emission of gamma particlesEnergy within the nucleus falls from a higher energy state to a lower energy stateIt does not change the atomic number or he atomic massLOOK FOR *

7.2 HALF LIFECarbon DatingAll organisms on earth contain carbonCarbons isotopes include:Carbon-12Carbon-14When an organism is aliveCarbon -12 = Carbon -14 When an organism dies, carbon-14 atoms start to decrease or decayRadiocarbon Dating measures the left over carbon-14 to determine age

Radiocarbon Dating...

Half Life ExamplesToday you have 100 bucks. After 3 days of spending... You only have 50 dollars left How long did it take you to use up HALF of your money?3 days

Today you have 10 g of strontium-90. After 29 years of decay, there is only 5 g left!How long did it take for HALF of the sample to decay?

THAT IS THE HALF LIFE OF YOUR MONEY!!!29 YEARS!!!! THAT IS THE HALF LIFE OF YOUR SAMPLEHALF- LIFEHalf life is the length of time it takes for HALF of the isotope to decay

We compare the rate of radioactive decay by comparing the half life of different isotopes

Decay curveWhen we graph the rate of radioactivity, it produces a decay curveThe decay curve for all isotopes look the same

ONLY DIFFERENCE is the length of time it takes for the sample to decayCALCULATING HALF LIVESTwo Types of IsotopesThe isotope that DECAYS is called the parent isotopeThe product AFTER DECAY is called the daughter isotope

Parent IsotopeDaughter IsotopeAs Parent Isotope decays and decreasesDaughter Isotope increases

Parent Isotope + Daughter Isotope = Total Initial massA parent isotope has an initial mass of 100 g. Its half life is 5 years. Complete the following table:Number of Half LivesTime ElapsedParent IsotopeDaughter IsotopeTotal Mass012340 years100 g0 g100 g5 years50 g50 g100 g10 years25 g75g100 g15 years12.5 g87.5 g100 g20 years6.25 g93.75 g100g40If this initial mass of the parent isotope is 400 g and it has a half life of 3 years. Complete the following table:Parent Isotope + Daughter Isotope = Total Initial massNumber of Half LivesTime ElapsedParent IsotopeDaughter IsotopeTotal Mass03 years400040016 years20020040029 years100300400312 years50350400415 years2537540041The Half Life Triangle of TimeTOTAL TIMEHALF LIFENumber of Half LivesThis line is divideThis line means multiplyALWAYS NEED AT LEAST 2 OF THESE VARIABLES42ExamplesIf a sample has a half life of 3 years and it has been decaying for a total of 12 years. What is the number of half lives it has gone through?TOTAL TIMEHALF LIFENumber of Half LivesNumber of Half LivesTotal TimeHalf Life12 years3 years4 yearsNumber of Half Lives43ExamplesIf a sample has gone through 5 half lives in a total of 25 years. What is the half life of the sample?TOTAL TIMEHALF LIFENumber of Half LivesHalf LifeTotal TimeNumber of half lives25 years5 half lives5 yearsNumber of Half LivesIf mass is given, draw a half life table!The initial mass of a sample is 100g. After several half lives, the final mass is 12.5g. How many half lives did the sample go through? # of Half LifeMass of parent0100g1250g2225g3212.5gNumber of half Life = 3!!!!Mass TableHow many half lives did a sample go through if the final mass is ? See a fraction??? CONVERT TO PERCENTAGE!!!!!Final mass= x 100%= 25%Initial Mass=100% # of Half LifeMass of parent0100%1250%2225%2Number of half Life = 2!!!!Steps to Calculating Half Life!!!LIST ALL VARIABLESInitial mass# ofHalf LifeFinal massHalf LivesTotal TimeDraw Mass TableTriangle of TimeSolve for Number of Half LivesSolve for variable of interestExample 1:Thallium-208 has a half life of 3 minutes. How long does it take for 120 g to decay to 7.50 g?List Variables:Initial mass:Final Mass:# of half livesHalf Life:Total Time:120g7.5g????3 min?????# Half LifeMass of parentMass of Daughter0120g160g230g315g47.5 g# of half life? 4!!!!!TOTAL TIME Life# of lifeTotal time = life x# of lives= 3 minX 4= 12 minutes!0g105g90g112.5g60g48Example 1:Gold-198 has a half life of 3 days. How much of a 96g sample of gold will be left after 9 days?List Variables:Initial mass:Final Mass:# of half livesHalf Life:Total Time:96g????????3 days9 days# Half LifeMass of parentMass of Daughter096g148g224g312g# of half life? 3!!!!TOTAL TIME Life# of life# of life =Total Time 3 days9 days life==3!!!!0g48g72g84g7.3 NUCLEAR REACTIONSNuclear ReactionsNuclear reaction is a process that changes the nucleus by gaining or losing a proton, neutron or electron and gamma raysA small change in the mass of an tom releases a large amount of energyExample: The nuclear fission of 1g of uranium 235 releases the same amount of energy as burning 2 tonnes of coalNUCLEAR FISSIONNuclear fission is the SPLITTING of the nucleus releasing 2 smaller nuclei, subatomic particles and nucleiNuclear Fission

Massive nucleus

2 smaller nuclei

Subatomic particles

EnergyNuclear FissionNuclear power plants produce power using nuclear fissionNuclear fission occurs because the nucleus is heavy with ALOT of protons. Like charges repel, therefore, these positively charged protons are pushing each other apartWhen pushed apart, ENERGY is produce and neutrons are released!Induce Nuclear FissionScientists induce a nuclear fission reaction by shooting a neutral, positive or negative particle into the nucleusHowever, it is easier to shoot a neutral particle, the neutron to induce a nuclear fission reaction

Chain ReactionAfter a nuclear reaction starts, it creates a chain reaction and keeps going!It is this continuous reaction that causes a violent nuclear explosion

Nuclear FusionProcess in which two low mass nuclei join together to make a more massive nucleus. Occurs at the core of the sun There is enough pressure and high enough temperatures to force isotopes to collide and fuse

Nuclear FusionBalance Nuclear Fusion ReactionsIn a balance nuclear fusion reactionThe combined atomic mass on the left must equal the combined atomic mass on the rightThe combined atomic number on the left must equal the combined atomic number on the right!Fusion Reactions H+ H He + + n + energy31104221923614156______10Remember whats on the left of the arrow must EQUAL whats on the right23492U3 n + Kr + Ba ____ + energy