Nuclear Chemistry Bravo 15 000 kilotons Nuclear Chemistry
Nuclear Chemistry Bravo – 15, 000 kilotons
Nuclear Chemistry • Title a new section in your notebook called Nuclear Chemistry • Also, get a periodic table in front of you.
Radioactive Decay • Radioactive decay is the spontaneous breakdown of an unstable atomic nucleus. It releases alpha, beta, and/or gamma radiation. • Very large atoms (atomic # 84 and up) are radioactive. Find these now on your periodic table. • Smaller atoms with an unstable number of protons and neutrons can be radioactive too. • Atoms will be unstable if they do not have the “right” ratio of protons : neutrons.
Draw a nucleus of Mg and U
• Strong Nuclear Force is an attractive force that holds heavy particles together in the nucleus, overcoming the electrostatic repulsion from positively charged protons. • This strong force keeps the nucleus from falling apart. • Only works at very close distances!!
Marie Curie • Isolated the radioactive elements Po, Ra and U • Coined the term “radioactivity” • Both Marie and her daughter Irene died of leukemia as a result of prolonged exposure to radioactive decay
• Radiation is the penetrating rays and particles emitted by a radioactive source. • Radioactivity is the process by which materials give off such rays.
Ernest Rutherford • Used a radioactive substance and charged plates to characterize the different types of radioactivity and the types of particles released. • Three Main Types of radiation: Alpha, Beta, and Gamma
Alpha Radiation Alpha decay is limited to VERY large, nuclei such as those in heavy metals.
Alpha Particle (α) • Alpha particles are composed of the same particles as the nucleus of a helium– 4 atom. • Have a 2+ charge • They are relatively large and slow moving (compared to speed of light) • It has relatively poor penetrating power; generally they are not dangerous unless ingested.
Beta Radiation Beta decay converts a neutron into a proton & ejects a beta particle (an electron).
Beta particle (β): Beta particles are essentially the same as an electron, they have very little mass and a charge of -1. Beta particles are created when a neutron in the nucleus ejects an electron and becomes a proton. Because of their low mass and moderate speed, they have a moderate level of penetration and damage.
• • Gamma Radiation (γ): On the electromagnetic spectrum Has no charge No mass, but travels at the speed of light Very high energy, high frequency radiation, like a super-powered ray of light or X-ray (just with much more energy) • Excellent penetration (lead/concrete suit!) • Very dangerous and damaging (has the most energy) • Gamma radiation is a byproduct of both beta and alpha decay
What can protect us?
Symbol Mass How it changes the nucleus Penetration Protection provided by… Danger Alpha Particle Emission Beta Particle Emission or or Heavy Light Decreases the mass number by 4 Decreases the atomic number by 2 Converts a neutron into a proton (Mass # doesn’t change) Increases atomic number by 1 Gamma Ray Emission No Mass No change to the nucleus Low Medium High Skin; paper Clothing; wood Lead; super thick concrete Low Medium High
Nuclear reactions are far greater than ordinary chemical reactions • http: //www. youtube. com/watch? v=h 7 vy. KDc. STa. E&f eature=related • http: //www. youtube. com/watch? v=v. Bdtw 5 Ha. PTQ& feature=related
Radioisotopes and Half Life - A radioisotope is an isotope which will undergo radioactive decay over time due to an unstable number of protons and neutrons in its nucleus. (It has too many or too few neutrons. ) -Most elements have at least one naturally occurring radioisotope. There is radioactive decay happening inside of you right now. -Most naturally occurring decay is at such low levels that it is harmless. -Some very unstable nuclei can decay very quickly, others will decay much more slowly.
A half life of a radioactive isotope is the time it takes for ½ of a sample of that isotope to decay. Knowing the half lives of different isotopes can be used to determine the age of an object. -Carbon-14 is an especially useful isotope for dating wooden artifacts or the remains of an organism. -Carbon-14 has a ½ life of 5, 730 years, making it useful for dating objects up to 60, 000 years old. Strontium-90 has a ½ life of 28. 8 years
Half-life Practice Sample Question 1: The ½ life of mercury-195 is 31 hours. If you begin with a 5. 00 g sample of 195 Hg, how much of it will be present after 93 hours?
Sample Question 2: Cobalt-60 has a half-life of 5. 25 years? If you started with 20. 0 grams of Cobalt-60, how much would remain after 10. 5 years?
Sample Question 3: A 64. 0 g sample of germanium-66 is left undisturbed for 25 hours. At this time, only 2. 0 g of germanium-66 remained. How many half lives did germanium-66 undergo?
• Where are the transuranic elements on the periodic table? • “trans” prefix means “after” • Uranic looks like what element? • = “after” Uranium • So transactinide elements would be where?
In a nuclear fission reaction, a large nucleus is split into two smaller nuclei of approximately equal mass. -During nuclear fission a very small amount of mass is “lost” as it is converted into an enormous amount of energy!
Fission - Splitting a heavy nucleus into two nuclei with smaller mass numbers.
In a chain reaction the neutrons produced at the end of one nuclear fission reaction are used to initiate a successive reaction. This can lead to a geometric expansion of fission reactions. -Atomic bombs are designed to create a “runaway” chain reaction which will use up all of the uranium present and create an incredibly powerful explosion. -Nuclear reactor plants do not contain enough 235 U to sustain a chain reaction. The major “meltdown” concern is the uncontrolled release of the radioactive waste produced during these reactions!
In a nuclear fusion reaction, two lighter nuclei are fused together to form a heavier nucleus. -This reaction also causes a small amount of mass to be “lost” as it is converted into a tremendous amount of energy. -Fusion is difficult to achieve due to the electrostatic repulsion of like -charged electron clouds and then by the repulsion of the like-charged protons in the nucleus. -Stars use fusion reactions as fuel. They overcome the repulsion problem with a combination of tremendous heat and gravitational force to force the nuclei together! -Cold Fusion research is aimed at finding a viable method for using fusion as a pollution free fuel source. It has not yet been successful.
Nuclear Symbols Mass number (p+ + no) Atomic number (number of p+) Element symbol
Types of Radioactive Decay v alpha production (a, He): helium nucleus v beta production (b, e): v gamma ray production (g):
Nuclear Stability Decay will occur in such a way as to return a nucleus to the band (line) of stability.
Deuterium – Tritium Fusion Reaction Fusion - Combining two light nuclei to form a heavier, more stable nucleus.
Albert Einstein used the formula: E=mc 2 to describe the possibility for the interchange between energy and mass. This formula shows that an absolutely enormous amount of energy can be derived from a small amount of matter!! E = mc 2 E = energy m = mass defect (mass lost during fission or fusion) c = speed of light (3. 0 x 108 m/s)
Energy and Mass Nuclear changes occur with small but measurable losses of mass. The lost mass is called the mass defect, defect and is converted to energy according to Einstein’s equation: DE = Dmc 2 Dm = mass defect DE = change in energy c = speed of light Because c 2 is so large, even small amounts of mass are converted to enormous amount of energy.
A Fission Reactor
Summary of Nuclear Chemistry • Take your knowledge and create a beautiful poster. • Include all CA standards on poster. • Winning lab group wins lunch with me.
CA Standards Students know protons and neutrons in the nucleus are held together by nuclear forces that overcome the electromagnetic repulsion between the protons. Students know the energy release per gram of material is much larger in nuclear fusion or fission reactions than in chemical reactions. The change in mass (calculated by E = mc 2) is small but significant in nuclear reactions.
CA Standards Students know the three most common forms of radioactive decay (alpha, beta, and gamma) and know how the nucleus changes in each type of decay. Students know alpha, beta, and gamma radiation produce different amounts and kinds of damage in matter and have different penetrations. Students know some naturally occurring isotopes of elements are radioactive, as are isotopes formed in nuclear reactions.
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