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Nuclear Chemistry
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Nuclear Reactions Chemical reactions What can NOT change in a chemical reaction? Nuclear Reactions: changes that occur in the nucleus of an atom The nucleus is unstable!! Most atoms have unstable nuclei.
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Why are some stable, while others are not? Primary Reason: ratio of the neutrons to the protons (n/p) An atom is most stable when ratio is 1:1 The maximum ratio of stability is around 1.5 : 1
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RadioactivityRadioactivity An unstable nucleus emits rays and particles, called radiation, to become stable The process is called radioactivity Gain stability by LOSING energy Discovery dealt a deathblow to Dalton’s theory of indivisible atoms
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Types of Radiation Alpha particle ( ) helium nucleus paper 2+ Beta particle ( -) electron 1- lead Gamma ( ) high-energy photon 0
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3 Radioactive Particles 1. Alpha Particle (+) It travels about 1/10 the speed of light (slowest) It is the largest, most massive particle It is the most dangerous if ingested It has the least penetrating ability - paper can stop this particle
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3 Radioactive Particles 2. Beta Particle (-) Fast accelerated electron Ejected when a neutron is converted to a proton in the nucleus Travels 1/4 the speed of light. It is lighter and faster than the alpha particle. Average penetrating ability - can be stopped by heavy clothing
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3 Radioactive Particles 3. Gamma Ray Not a particle; it is high energy electromagnetic radiation Has no mass and no charge. Always accompanies either beta or alpha radiation. Travels at the speed of light. Highest penetrating ability - can be stopped by heavy shielding such as lead.
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Radioactive Particles Summary
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Nuclear Decay Alpha Emission parent nuclide daughter nuclide alpha particle Numbers must balance!!
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Nuclear Decay Beta Emission A neutron is converted in the nucleus of an atom A new atom is formed whose atomic number is increased by 1
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Nuclear Decay Gamma Emission Always accompanies alpha and beta emissions. Transmutation One element becomes another.
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Half-lifeHalf-life Half-life (t ½ ) Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable.
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So, what does this mean? Let’s say you have 100 g of radioactive C- 14. The half-life of C-14 is 5730 years. How many grams are left after one half- life? How many grams are left after two half- lives? 50 g 25 g
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Common Radioisotopes IsotopeHalf-LifeRadiation Emitted Carbon-145,730 years Radon-2223.8 days Uranium-2357.0 x 10 8 years Uranium-2384.46 x 10 9 years
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Half-lifeHalf-life r :final mass i :initial mass n :# of half-lives To find the remaining amount…
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More Half-Life Equations Total time passed (p) = n x t 1/2 To find the half-life t 1/2 = To find the # of half lives that have passed… n =
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Half-lifeHalf-life Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s? GIVEN: t ½ = 5.0 s i = 25 g r = ? p = 60.0 s n = 60.0s ÷ 5.0s =12 WORK : r = i (0.5 ) n r = (25 g)(0.5) 12 r = 0.0061 g
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You try it! If the half life element A is 3 hours and you have 90 grams of it, how many grams would be left after 9 hours?
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F ission splitting a nucleus into two or more smaller nuclei 1 g of 235 U = 3 tons of coal
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F ission chain reaction - self-propagating reaction
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FusionFusion combining of two nuclei to form one nucleus of larger mass thermonuclear reaction – requires temp of 40,000,000 K to sustain 1 g of fusion fuel = 20 tons of coal occurs naturally in stars
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