Nuclear Chemistry Review & Calculations Ms. Sipe

Nuclear Chemistry Reactions in the nuclei of atoms Nuclear reactions Changes in the nuclei Involve the emission of energy- rays or particles Not affected by temperature, pressure , or catalysts like regular chemical reactions In chemical rxns bonds break and rearrange to form new substance (reactivity based on what subatomic particle?)

Nuclear Chemistry Types of nuclear reactions Fusion- combining of nuclei, releases a lot of energy Stars and the sun Fission- splitting of nuclei into smaller nuclei Radioactive Decay or radioactivity Reactions begin with unstable isotopes called radioisotopes that undergo change to become stable

Nuclear Fusion The energy emitted by the sun results from nuclear fusion. Fusion occurs when nuclei combine to produce a nucleus of greater mass. In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei. A LOT OF ENERGY PRODUCED! The reaction also produces two positrons.

Nuclear Fission More neutrons are released by the fission. The figure below shows how uranium-235 breaks into two smaller fragments of roughly the same size when struck by a slow-moving neutron. U Uranium-235 (fissionable) 235 92 Uranium-236 (very unstable) 236 Ba Barium-142 142 56 Kr Krypton-91 91 36 3 n 1 Neutron More neutrons are released by the fission. These neutrons strike the nuclei of other uranium-235 atoms, which cause chain reactions.

Recap: Fusion vs Fission Combining 2 light nuclei to form a heavier nucleus Requires high T & P Powers stars & sun Splitting a heavy nucleus into 2 nuclei with smaller mass # Radioactive decay (w/o neutron)

Types of Nuclear Emissions/Radiation Characteristics of Some Types of Radiation Type Consists of Symbol Charge Mass (amu) Common source Penetrating power Alpha radiation Alpha particles (helium nuclei) or a 2+ 4 Radium-226 Low (0.05 mm body tissue) Beta radiation Beta particles (electrons) or b 1– 1/1837 ~ 0 Carbon- 14 Moderate (4 mm body tissue) Gamma radiation High-energy electromagnetic radiation g Cobalt-60 Very high (penetrates body easily)

Mass # decreases by 4 & Atomic # decreases by 2 Alpha Radiation U 238 92 Uranium-238 Th + 234 90 Thorium-234 He (a emission) 4 2 Alpha particle Radioactive decay Mass # decreases by 4 & Atomic # decreases by 2

Carbon-14 (radioactive) Beta Radiation C 14 6 Carbon-14 (radioactive) N + 7 Nitrogen-14 (stable) e (b emission) –1 Beta particle → n 1 Neutron p + Proton e –1 Electron (beta particle) → An electron resulting from the breaking apart of neutrons in an atom # of protons increases while #of neutrons decreases. Same Mass #; Atomic # increases by one

Gamma Radiation Ra + Th He + g → Pa + Th e + g → 226 88 Radium-226 Th 230 90 Thorium-230 He + g 4 2 Alpha particle Gamma ray → Pa + 234 91 Protactinium-234 Th 90 Thorium-234 e + g –1 Beta particle Gamma ray → Nuclei often emit gamma rays along with alpha or beta particles during radioactive decay. Gramma ray – no mass/no electric charge - Does not alter the atomic number or mass number of an atom.

Balancing Nuclear Equations U-238 alpha decay- Helium particle emitted 23892U  ? + 23490Th Na -24 beta decay- electron emitted 2411Na  ? + 2412Mg

Balancing Nuclear Equations U-238 alpha decay- Helium particle emitted 23892U  42He + 23490Th Na -24 beta decay- electron emitted 2411Na  0-1e + 2412Mg

Nuclear Chemistry Application of Radioisotopes Smoke Detectors Food Irradiation Archaeological Dating Medical Uses Nuclear Power Nuclear Weapons

Applications of Nuclear Reactions Nuclear power and Nuclear weapons Most common nuclear fuel: Uranium-235, Plutonium-239 Difference btw power & weapon Power – can control E release & convert to heat Weapon – uncontrolled release of E

Power Nuclear energy – Fr ~80%, US 20%, Japan 35%, Germany – 30% Weapon Fission weapons – Atomic bombs (A-bomb) Fusion weapons – Hydrogen bombs (H-bomb) Manhattan Project WWII Submarines – that use nuclear energy stay longer underwater

A Few Pros and Cons No more need for oil Not using fossil fuel Fission > energy compared to gasoline Will have unlimited amounts of energy (esp if fusion works; sun) No need for us to depend on other countries Hard to control Nuclear waste Pollution Radiation Nuclear reactor – away from large population, waterways, earthquake zones Japan reactor explosion – then cooling system fails so further explosion or leak of radioactive material can occur Nuclear reactor overheating – explode like a nuclear weapon Nuclear weapon – destructive potential

A half-life (t½) is the time required for one-half of the nuclei in a radioisotope sample to decay to products. After each half-life, half of the original radioactive atoms have decayed into atoms of a new element.

Half-Lives of Some Naturally Occurring Radioisotopes Half-Life Comparing Half-Lives Half-lives can be as short as a second or as long as billions of years. Half-Lives of Some Naturally Occurring Radioisotopes Isotope Half-life Radiation emitted Carbon-14 5.73 × 103 years b Potassium-40 1.25 × 109 years b, g Radon-222 3.8 days a Radium-226 1.6 × 103 years a, g Thorium-234 24.1 days Uranium-235 7.0 × 108 years Uranium-238 4.5 × 109 years

Half-Life Comparing Half-Lives Uranium-238 decays through a complex series of unstable isotopes to the stable isotope lead-206. The age of uranium-containing minerals can be estimated by measuring the ratio of uranium-238 to lead-206. Because the half-life of uranium-238 is 4.5 × 109 years, it is possible to use its half-life to date rocks as old as the solar system.

Half Life Calculations The half-life of beryllium-11 is 13.81 seconds. Let's say you start with 16 grams of 11Be. After 13.81s, you have 8 grams of that isotope left (the rest will have decayed to something else). After another 13.81s, you have 4 grams left; 13.81 seconds more, and you have 2 grams left……so after 3 half lives berllium-11 decayed from 16g to 2 g. In chemistry, you set up tables like this:   Time Amount remaining 0 s 16 grams 13.81 s 8 grams 27.62 s 4 grams 41.43 s 2 grams

Practice Problem… In a particular bone sample, you have 80g of a parent and 560g of a daughter isotope. The half life of the sample is 100 years. How old is the bone? 560g + 80g = 640 g for the original parent 640  320  160  80 equals 3 half lives (3)(100 yrs) = 300 years old Now, you try some…

Closure: Germany said it would close all of its 17 nuclear reactors by 2022, a sharp policy reversal that will make it the first major economy to quit atomic power in the wake of the nuclear crisis in Japan. Do you think USA should do the same? Provide 3 reasons to support your answer