Nuclear Chemistry

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/radioa7.swf

Radioactive decay movie http://streaming.discoveryeducation.com/index.cfm

Radioactivity: Decay of, and emission of electromagnetic radiation and particles from the nuclei of certain elements that spontaneously desintegrate. Atoms with Atomic Number greater than 83 (unstable)

ALPHA DECAY: Alpha emitter (+): He, α (4amu,charge 2+) Ra → Rn + He Atomic number decreases by 2. (2p) The mass number decreases by 4. (2p+2n)

Beta Decay: A beta particle is a high speed electron. Pb → Bi + e Th → Pa + e Atomic number increases by 1 (1p) Mass number remains the same.

GAMMA RADIATION (γ) Are not particles: no mass, no charge. Similar to X-rays, but greater energy.

Positron Emission: o amu., 1+; e., moderate power. p → n + e K → Ar + e Atomic number decreases by 1 Atomic mass remains the same.

As is clear, the final product of uranium-235 decay is lead. Decay series of  235U (based on data from the U.S. Department of Energy): 235U --> 231Th + 24 α + γ 231Th --> 231Pr + β- + γ 231Pr --> 227Ac + 24 α + γ 227Ac --> 227Th + β- or 227Ac --> 223Fr + 24 α 227Th --> 223Ra + 24 α + γ or 227Ac --> 223Ra + β- + γ 223Ra --> 219Rn + 24 α 219Rn --> 215Po + 24 α + γ 215Po --> 211Pb + 24 α 211Pb --> 211Bi + β- + γ 211Bi --> 207Tl + 24 α + γ 207Tl --> 207Pb + β- As is clear, the final product of uranium-235 decay is lead.

Figure 6: A basic diagram of nuclear fission.                                                                                                                                                            Figure 6: A basic diagram of nuclear fission.

Decay of polonium-218 by alpha () emission. – Nuclear Decay. Practice Write equations for the following nuclear decay reactions. Make sure that both mass numbers and atomic numbers are balanced on each side. Decay of polonium-218 by alpha () emission. Decay of carbon-14 by beta (-) emission. Decay of chlorine-32 by positron (+) emission. Decay of promethium-142 by electron capture.

What is Half-life? 1. Half-life is the time taken for half of the radioactive nuclei to decay.

How many half-lives have gone by? _________________________ Half-life The half-life of phosphorous-30 is 2.5 min. If you start with 35 g of phosphorus-30, how many grams would remain after 20.0 min? The half-life of polonium-210 is 138.4 days. How many milligrams of polonium-210 remain after 415.2 days if you start with 2.0 mg of the isotope? 20.0 g of a radioactive isotope are present at 1:00 p.m., and 5.0 g remain at 2:00 p.m. How many half-lives have gone by? _________________________ How long is the half-life of the isotope? _________________________ Predict how many grams will be left at 2:30 p.m. _________________________

Nuclear equations C  e + N Po  He + Pb U  n Ba + 3 Kr Q. Write the beta decay for C-14 14 14 C  e + N 6 -1 7 209 4 205 Q. Write the alpha decay for 209Po Po  He + Pb 84 2 82 Q. Complete this fission reaction U 235 92  n 1 Ba 139 56 + 3 94 Kr 36 In all cases, charge and mass must be balanced

Discovery of Radioactivity Radioactivity is the release of energy or particles when an atom disintegrates (demo) Radioactivity was discovered when minerals were exposed to film through an opaque cover The 3 types of radioactivity can be shown by passing emissions through an electrical field: Phosphorescent zinc sulfide detection screen + – Strong magnetic or electrostatic field Lead block Radioactive substance   

Types of Radioactivity Types of radiation: 1) a, 2) b, 3)  Alpha () particles are symbolized as 42He Beta () particles (essentially electrons) are 0–1e Gamma (g) rays are symbolized as 00 You can determine the composition of each: a: mass of 4 u, charge of +2 (2 p+, 2 n0, 0 e–) Other symbols: proton = 11p, neutron = 10n There are different terms to describe the different types of nuclear reactions “alpha decay” means an a particle is given off. Other: beta decay, fusion (meaning to bring together), fission (meaning to break apart)

Risk of Radioactivity Biological exposure; (mutations, cancer) Radioactive waste ( Isotopes w/long half live) Danger of accidents (Chernobyl, Three Mile Island, Fukushima Daiichi plant.)

Chernobyl https://www.youtube.com/watch?v=iLJuQQDPY8Y#t=161.939396

Benefits Nuclear power- electricity. Tracers: I-131, Carbon-14(short half lives) Food: used in food preservation Geology and Archeology: Dating Rocks: U-238/Pb-206 Dating Fossils; Carbon dating C-14/C-12

Below is a graph showing the half life of the isotope, Americium-241 Below is a graph showing the half life of the isotope, Americium-241. Note that in theory, some of the original substance will always remain as the amount of substance only reaches zero as time approaches infinity. Below is a graph showing the half life of the isotope, Americium-241. Note that in theory, some of the original substance will always remain as the amount of substance only reaches zero as time approaches infinity. Below is a graph showing the half life of the isotope, Americium-241. Note that in theory, some of the original substance will always remain as the amount of substance only reaches zero as time approaches infinity.