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The Nucleus of the Atom. Chapter 12. Great Idea: Nuclear energy depends on the conversion of mass into energy. Empty Space, Explosive Energy. Empty space: If a nucleus is the size of a baseball, the electrons are about 15 miles away. Relation of atom to nucleus
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The Nucleus of the Atom Chapter 12 Great Idea: Nuclear energy depends on the conversion of mass into energy
Empty Space, Explosive Energy • Empty space: • If a nucleus is the size of a baseball, the electrons are about 15 miles away. • Relation of atom to nucleus • What goes on in the nucleus has almost nothing to do with the atom’s chemistry, and vice versa • The energies available in the nucleus are much greater than those available among electrons • Mass and energy: E=mc2 • In the US, each person uses about 10,000 kwh energy each year. How much mass is it corresponding to?
The Organization of the Nucleus • Atomic nuclei sometimes break into small fragments. • Nucleus is made up of smaller pieces: Protons and Neutrons Particles Mass Charge Proton 1 +1 Neutron 1 0 Electron 1/1860 -1 (mass 1 = 1.67x10-27kg; charge 1= 1.6x10-19C) • Electrons give an atom its size, and nucleus gives atom its mass
Atomic Numbers, Isotopes, and the Mass Number • Atomic number • Number of protons in nucleus. • Defines chemical behavior • Isotopes • Elements with same number of protons but different numbers of neutrons. Example: C-12, C-13, C-14 • About 2000 isotopes have been documented • Mass number • Total protons and neutrons
(Continue) Example 12-1 Inside the atom 1. We find an atom with 9 protons and 8 neutrons in its nucleus and 10 electrons in orbit. a. What element is it? (Fluorine) b. What is its mass? c. What is the electric charge? d. How is it possible that the number of protons and electrons are different? Example 12-2 A heavy element 2. How many protons, neutrons, and electrons are contained in the atoms when it has a charge of +2?
(Continue) Problems: Page 259 1. Use the periodic table to identify the element, atomic number, mass number, and electrical charge of the following combinations: a. 7 protons, 7 neutrons, 10 electrons b. 8 protons, 8 neutrons, 8 electrons 2. Us the periodic table to determine how many protons and neutrons are in each of the following atoms: a. C-13 b. Zn-66
The Strong Force • Strong force: • Force that holds nucleus together • Operates only over very short distances characteristic of the size of nucleus Binding energy: The mass of the nucleus is always slightly less than the sum of the masses of the protons and neutrons – some of their mass is converted into the energy that binds them together
What is Radioactive? • Radioactivity or radioactive decay: • spontaneous release of energetic particles of the nuclei • 99.999% of atoms in everyday surroundings are stable: nuclei will never change • Some kinds of nuclei are not stable: U-238 • Radiation: • the emitted particles: measured by Geiger counter
The Kinds of Radioactive Decay • Alpha Decay • Release of Alpha particle • Composed of 2 protons and 2 neutrons (same as the nucleus of a He-4) • Reduces the mass and changes the chemical identity of decaying nucleus • Alpha particles travels at very high speed when leaving parent nucleus, collisions, convert energy to heat. About half of Earth’s interior heat comes from this. • Beta Decay • Emission of electron • Gamma Radiation • Electromagnetic radiation
Radiation and Health • Why is nuclear radiation so dangerous? • Alpha, beta, and Gamma radiations all carry a great deal of energy • Ionization: Stripping away an atom’s electrons Great deal of radiation causes sickness or death: Hiroshima and Nagasaki’s atomic bombs Long-term effects • Cancer • Birth defects
Half-Life • Half-life • Average time for decay of ½ batch of radioactive isotopes • Example: 100 nuclei at beginning, half-life 20 minutes. • Wide range of half-lives: • U-222, half life a tiny fraction of a second • U-238, half life in billions of years • Half-life cannot be predicted but can be easily measured.
Radiometric Dating • Radiometric dating: • Determine the age of materials • Depends on Measurement of half-life of radioactive materials Carbon-12: 99% Carbon-13: 1% Carbon-14: radioactive isotope • no more than 1 in every trillion • Half-life = 5700 years • Is about the same in all living things • Stop taking in Carbon in any form from the time of death • Geology: • when object is more than 50,000 years old • Need longer half-lives • Potassium-40 1.25 billion years • Uranium-238 49 billion years
Decay Chains • Decay chains • Series of decays • Continues until stable isotope appears
Indoor Radon • Decay of Uranium-238 • Radon-222 • Can build up in well-insulated, tightly scaled buildings • Expose to high radon levels is dangerous because each radon atom will undergo at least five more radioactive decay events in a few days. • Test radon • Increase ventilation • www.epa.org/radon/pubs/citguide.htmlA Citizen's Guide to Radon: The Guide to Protecting Yourself and Your Family From Radon
Nuclear Fission • Fission • Splitting of nucleus • Chain reaction Critical mass: minimum mass for a self- sustaining chain reaction
(Continue) • Nuclear Reactor • Extracts energy from nuclear reaction • Confine dangerous radioactive materials • Meltdown: • Flow of water to fuel rod is interrupted, overheat cause the fuel rod to melt
Fusion • Fusion • two hydrogen nuclei combine together • Some mass converted into energy The nuclear reaction powers the sun and other stars
Nuclear Weapons The gun concept used in the Little Boy uranium bomb design
Nuclear Waste Management • There are 131 temporary repositories located in 39 different states • Should we confine all nuclear waste in a single, remote, long-term site (Yucca Mountains in Nevada)? • Supporters • Opponents
Homework • Self-quiz of Chapter 12 • More Exercises: Chapter 12: 3-9, 11,12, 19-27, 29, 35,36,38-40