atoms chapter 4. protons positively charged = +1 approximately 1 amu (atomic mass unit) located in...
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AtomsChapter 4
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Protons
•Positively charged = +1
•Approximately 1 amu (atomic mass unit)
•Located in the nucleus
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Neutrons
•Neutrally charged = 0
•Approximately 1 amu
•Located in the nucleus
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Electrons
•Negatively charged = -1
•Relatively small mass (0.0005 amu)
•Located in the space surrounding the nucleus
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Atoms
•Neutral charge
•Same number of protons as electrons to balance the charge
•Atomic number = # protons and # electrons
•Atomic mass = # protons + # neutrons
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Isotopes
•Same number of protons (atomic number the same)
•Different number of neutrons (atomic mass different)
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Ions•Same number of
protons (same atomic number)
•Same number of neutrons (same approximate atomic mass)
•Different number of electrons (has a charge)
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Regular Average•All samples are weighted equally
•Example : If a student took 5 tests each test is worth 1/5th or 20% of the final grade
• Can multiply each test by 1/5th
•OR add all the tests and divide by 5
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Weighted Average•Not all samples are weighted equally
•Example: A student takes 5 tests. The first test is worth 40%, the second is worth 30%, and the other are each worth 10%
•Multiply each test by what it is worth
•Add up
•Atomic weight on periodic table
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Radioactive DecayChapter 4 and Chapter 25
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Radioactive Decay• The tendency of an element to
spontaneously emit radiation until it forms a stable atom
• Unstable nuclei based on ratio of neutrons to protons
• Often results in the formation of a different element
• Radioisotopes: isotopes of atoms with unstable nuclei
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Stability
•Ratio between neutrons:protons
•Closer to 1:1 = more stable (elements of atomic number < 20)
•Closer to 1.5:1 = more stable (elements with very large atomic numbers)
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Types of Radioactive Decay:
Alpha Particle• 2p+, 2n
• 2+ charge on particle
• Basically an He atom
• Slow moving and not good at penetrating
• Happens to very large atoms
• Lose both proton and neutrons
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Types of Radioactive Decay:
Beta Particles• 1e-
• -1 charge
• Move very fast
• Neutron breaks down to a proton and an electron
• Loses a neutron and gains a proton
• Happens to really large atoms
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Types of Radioactive Decay: Gamma
Particles•Mostly energy
•Has 0 mass
•No charge
•Accompanies alpha and beta radiation
•Cannot form new atoms
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Types of Radioactive Decay: Positron
Emission• Emission of a positron from the nucleus
• Positron = particle the same mass as an electron but the opposite charge
• Proton converted to neutron and positron
• Loses proton, gains neutron
• Happens to very small atoms
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Types of Radioactive Decay: Electron
Capture•Nucleus draws in a surrounding electron
•Combines with a proton to form a neutron
•Loses a proton, gains a neutron
•Happens to small atoms
•Also emits a photon
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Nuclear Reactions
•Atomic number and atomic mass are conserved
•Reactants = products
•Problems 69 - 72 p. 837
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Transmutation
•The conversion of one atom of an element to another element
•Via nuclear reactions
•Can happen naturally (all elements above #83)
•OR can be induced
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Half - Life• Radioactive decay can be
measured in half-lives
• Half-life = time required for one half of a radioisotope’s nuclei to decay
• Amount remaining = initial amount * 0.5^n
• n = the # of half-lives
• n = t/T where t = elapsed time, T = half life
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Nuclear Reactions
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Nuclear Reactions
•Much more powerful than chemical reactions
•Energy released is greater
•Fission and Fusion
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Fission• Heavy, unstable atoms fragment into smaller atoms to
increase their stability
• Initiate by hitting with a neutron
• Smaller products form, extra neutrons
• Extra neutrons can trigger more fission reactions = chain reaction
• Atom must be big enough to initiate and maintain a chain reaction = critical mass
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Fusion
•Small atoms bind to create more stable atoms
•Release large amounts of energy
•Take really high heat to initiate and maintain reaction (40 million K)
•Thermonuclear reactions
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Nuclear Power Plants• Fission Reactions
• Fuel rods contain large atoms (uranium-235)
• Additional rods contain atoms that can absorb extra neutrons
• Positioning can determine how many neutrons are absorbed and the speed of the rxn
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Power Generation
•Fission reactions produce a lot of heat
•Heat absorbed by a cooling system of water
•Used to generate steam that drives turbines to produce power
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Problems•Tight balance between out of control
chain reactions and producing adequate power
•Continual adjustment
•Some products are extremely radioactive with long half-lives, waste
•Containment structures to shield radioactivity