2.  Chemical Properties  Determined by ▪ number of electrons ▪ positions of electrons

3.  Nuclear Properties  Determined by ▪ Size of the nucleus ▪ Ratio between neutrons and protons

4.  Atomic Nuclei are either  Stable ▪ Vast majority of atoms are stable  Unstable ▪ Source of radiation ▪ Used in Nuclear Reactors ▪ Powers Nuclear Bombs

5.  Naturally Radioactive Nuclei  Have an neutron/proton ratio that is abnormal  Exist Outside Band of stability ▪ 1 neutron for every 1 proton (up to element 20) ▪ 1.5 neutrons for every 1 proton (elements from #20-#82)  Have a very heavy nucleus ▪ All atoms with an atomic number past 82 are unstable

7.  Radioactive Isotopes  Have unstable nuclei  Exist outside the band of stability  Emit several different types of radiation ▪ (to become stable nuclei)

8.  Emission of Radiation is one way for an unstable nucleus to become a stable one.  Nuclear Radiation  Is usually ▪ Alpha ▪ Beta ▪ Gamma

9.  Nuclear Radiation  Alpha: He +2 charge: helium-4 nuclei, travel low speed, easily stopped  Beta: e -1 charge: penetrate 100 times more than alpha  Gamma: γ no charge, hi speed electromagnetic radiation of very short wavelengths, bursts of energy emitted from nucleus 4242 0 0000

10.  More Nuclear Radiation  Positrons: e +1 charge: exact same properties as electron, with positive charge (form of anti-matter)  Electron capture: e e- pulled into nucleus, causes p + to convert into n 0  Neutron bombardment: n 0 fired into nucleus, bumps p + out. (Used in nuclear reactors to start chain reaction) 0 +1 0

11.  All of these rxns began w/ an unstable nucleus which spontaneously emitted some form of radiation.  Conversion of one element to another is called transmutation.  It can also be induced by bombarding a stable nucleus with high energy , ,  or neutrons.

12.  Radioactive Decay Series: the series of nuclear reactions an unstable atom undergoes to become stable

13.  Starting atom: U-238  Ending atom: Pb-206  Why did we stop at Pb-206?

14.  Three most common series:  U-238  Pb-206  U-235  Pb-207  Th-232  Pb-208  Why do they all stop at lead?

15.  Alpha emission:  radium-226 decays emitting alpha particles Ra  He + Rn 226 88 222 86 4242

16.  Alpha emission:  Radon-222 decays emitting alpha particles Ra  He + _______ 222 86 4242

17.  Beta emission:  thorium-234 undergoes beta decay: Th  e + Pa 234 90 234 91 0

18.  Beta emission:  lead-214 undergoes beta decay: Pb  e + __________ 214 82 0

19.  Gamma Radiation:  No charge  no particle change to nucleus  no equation needed

20.  Positron emission:  Phosphorus-32 emits a positron P  e + + ________ 32 15 0 +1

21.  Neutron Bombardment:  Nitrogen-14 is bombarded with neutrons N + n 0  p + + ________ 14 7 1010 1111

22. 1. alpha decay of Uranium-238 2. alpha decay of Barium-139 3. beta decay of Radon-222 4. beta decay of carbon-11

23. 5. Oxygen-15 undergoing positron emission 6. neutron bombardment of U-235

24.  The time it takes for half of a radioactive substance to decay  Example:  The half-life of strontium-90 is 28 years. If you started with 10 g of Sr-90, how much remains after 28 years?  56 years?  84 years?  112 years?

25.  http://phet.colorado.edu/sims/nuclear- physics/alpha-decay_en.jnlp http://phet.colorado.edu/sims/nuclear- physics/alpha-decay_en.jnlp

26.  Radium’s half-life = 1620 yrs.  Starting with 40g of Ra, how much remains in 1620 yrs?  3240 yrs?  4860 yrs?

27.  The half-life of I-131 is 8 days. If only 1/8 th the original amt of this isotope of I remains, how old is the I-131 ?

28.  After 3 years only 1/64 th of the original mass of an element remained. What was its half life?

29.  Carbon in living organisms is a constant ratio of C-14 (radioactive) to C-12 (stable). When organism dies (stops breathing in C-14 from atmosphere), no fresh C-14 replaces the C-14 decaying in its tissues.  C-14 has a half life of 5700 years.

31.  C-14 dating CANNOT be used to date objects that are more than about 50,000 yrs old.  1. after 8 half-lives the radioactivity is too low to be measured accurately (1/2) 8 = 1/256 th  2. can’t be sure that the ratio of C-14 to C-12 was the same long ago as it is now (depends on solar activity & ocean pH)

32.  An ancient wooden dish is found to contain 25 % of the amt of C-14 that is in a living tree. About how old is this dish?  A museum mummy contains 1/8 th of the amt of C- 14 as a living Egyptian. How old is the mummy?