Presentation on theme: "Nuclear Chemistry Nuclear chemistry is the study of the changes of the nucleus of atoms. Nuclear Reactions involve changes within the nucleus where as."— Presentation transcript:
1 Nuclear ChemistryNuclear chemistry is the study of the changes of the nucleus of atoms.Nuclear Reactions involve changes within the nucleus where as chemical reactions involve the loss, gain or sharing of electrons.
2 The NucleusRemember that the nucleus is made up of protons and neutrons. The are collectively called nucleons.
3 RadioactivityA stable nucleus holds together well. An unstable nucleus will decay or break down, releasing particles and/or energy in order to become stable.An atom with an unstable nuclei is considered “radioactive”.
4 Nuclear Transformations Nuclear transformations can be induced by accelerating a particle and colliding it with the nuclide.These particle accelerators are enormous, having circular tracks with radii that are miles long.
5 There are several ways radioactive atoms can decay into different atoms! Transmutation:Type of nuclear reaction that will change the number of protons and thus will create a different element.Atoms with an atomic number larger than 92 are created through this process
6 He α U Th He Alpha Decay Loss of an -particle (a helium nucleus) Atomic number decreases by 2 and mass number decreases by 4Penetrating Power: LOW: Can be blocked by clothing or thin paperExampleORHe42α42U23892Th23490He42+
9 e I Xe e Beta Decay Loss of a -particle (a high energy electron) Atomic number increases by 1 and mass number stays the same. A neutron becomes a proton and a high speed electron that is discharged from the nucleus.Penetrating Power: Medium: Can be blocked by thin metal or woodExample−1eorI13153Xe54e−1+
12 Gamma EmissionLoss of a -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle)Atomic number and mass number stays the samePenetrating Power: High: Can only be blocked by thick metal or thick concreteExampleI13153e+
14 RadioactivityRadioactive isotopes decay at a characteristic rate measured in half life.A half life is the time required for half of the amount of radioactive atoms to decay. The time ranges from seconds to millions of years
15 Np Pu ____ Examples Beta decay of zircomium-97 Alpha decay of americium-241Alpha decay of uranium-238Complete this:Np23593Pu23994____+
16 Common Radioactive Isotopes Isotope Half-Life Radiation EmittedCarbon ,730 years b, gRadon days aUranium x 108 years a, gUranium x 109 years a
17 Radioactive Half-Life After one half life there is 1/2 of original sample left.After two half-lives, there will be1/2 of the 1/2 = 1/4 the original sample.
18 Graph of Amount of Remaining Nuclei vs Time A=Aoe-ltA
19 Half Life Calculations HOW TO’s1. To calculate the number of half lives, divide the half life (T1/2) into the total time (T). T/T1/2 = # of half lives 2. Use the equation to calculate remaining amount left over after a certain number of half lives have passed.Amt remaining = (initial amt) (.5)n (# of half lives)
20 ExampleYou 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?
21 ExamplesSuppose you have 20 grams of sodium-24. Its half-life is 15 hours. How much is left over after 60 hours.
22 ExamplesUranium-238 has a half life of 4.46 x 109 years. How long will it take for 7/8th of the sample to decay?
23 ExamplesThe half life of radium-222 is 38 s. How many grams of a 12.0 g sample are left after 114 s?
24 Examples A sample of 3x107 Radon atoms are trapped in a basement that is sealed. The half-life ofRadon is 3.83 days. How many radon atomsare left after 31 days?answer:1.2x105 atoms
25 Nuclear Fission: How does one tap all that energy? Large atoms split into smaller atoms that generate huge amounts of energy.Carried out in nuclear reactors.Could result in a chain reaction of fission like the atomic bomb
26 Nuclear FissionBombardment of the radioactive nuclide with a neutron starts the process.Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons.This process continues in what we call a nuclear chain reaction.
27 Nuclear FissionIf there are not enough radioactive nuclides in the path of the ejected neutrons, the chain reaction will die out.Therefore, there must be a certain minimum amount of fissionable material present for the chain reaction to be sustained: Critical Mass.
28 Nuclear ReactorsIn nuclear reactors the heat generated by the reaction is used to produce steam that turns a turbine connected to a generator.
29 Nuclear ReactorsThe reaction is kept in check by the use of control rods.These block the paths of some neutrons, keeping the system from reaching a dangerous supercritical mass.
30 Nuclear Fusion Fusion would be a superior method of generating power. The good news is that theproducts of the reaction arenot radioactive.The bad news is that in order to achieve fusion, the material must be in the plasma state at several million kelvins.Tokamak apparati like the one shown at the right show promise for carrying out these reactions.They use magnetic fields to heat the material.
31 Nuclear Fusion Smaller atoms are combine to form a large atom. Occurs in the sun and starsGenerates huge amounts of energy