nuclear chemistry the study of the structure of atomic nuclei and the changes they undergo
TRANSCRIPT
Is radiation dangerous?
Is nuclear power a good choice? What is nuclear energy?
Are nuclear energy and nuclear bombs both dangerous?
Guiding Questions
Radioactive Decay
• Discovered by Antoine Henri Becquerel in 1896– He saw that photographic plates developed bright
spots when exposed to uranium metals
As you may recall, isotopes are atoms of the same element that have different numbers of neutrons.
Isotopes of atoms with unstable nuclei are called radioisotopes
Stable Isotopes -Atoms that do not release protons or neutrons from the nucleus and ARE NOT RADIOACTIVE.
Unstable Isotopes - Atoms that spontaneously release protons and neutrons from its nucleus. These isotopes ARE RADIOACTIVE.
Radioactive Isotopes
Band of Stability • The region on a graph
which indicates all stable nuclei when the number of neutrons are compared to the number of protons for all stable nuclei
Nuclear Reactions• Nuclear reactions are different from chemical
reactions
Chemical Reactions
Mass is conserved (doesn’t change)
Small energy changes
No changes in the nuclei; involve ONLY valance electrons
Nuclear Reactions
Small changes in mass
Huge energy changes
protons, neutrons, electrons and gamma rays can be lost or gained
Mass Defect
• Some of the mass can be converted into energy
• Shown by a very famous equation!
E=mc2
Energy
Mass
Speed of light
Types of Radiation • The effect of an electric field on three types of
radiation is shown.
• Positively charged alpha particles are deflected toward the negatively charged plate.
Products of Natural Radioactivity Mass
Particle* Symbol Charge Number Identity
Alpha 4 a 2+ 4 Helium nucleus2
Beta 0 b 1- 0 Electron-1
Gamma 0 g 0 0 Proton of light0
*Sometimes a stream of any of these types of particles is called a ray, as in gamma ray,
Beta decay, Nuclear changes that accompany the emission of a beta particle.
Types of radioactive decay
• As you can see from the symbol, both the subscript and superscript are zero.
• Gamma rays are high-energy (short wavelength) electromagnetic radiation. They are denoted by the symbol.
particle emission
• Thus, the emission of gamma rays does not change the atomic number or mass number of a nucleus.
• Gamma rays almost always accompany alpha and beta radiation, as they account for most of the energy loss that occurs as a nucleus decays.
Induced Nuclear Reactions
• Scientists can also force ( = induce) nuclear reactions by smashing nuclei with alpha, beta and gamma radiation to make the nuclei unstable
4 14 17 12 7 8 1 + N O + p
4 14 17 12 7 8 1He + N O + H
or
BALANCING NUCLEAR EQUATIONS1. The sums of mass numbers (left superscripts) on each
side must be equal.2. The sums of atomic numbers or nuclear charges (left
subscripts) on each side of the equation must be equal.
Examples:238U 4He + 234Th 92 2 90
214Pb 0 + b 214Bi 82 -1 83
Balancing Nuclear Equations
Complete the following nuclear equations:
1. 217At 213Bi + ?
2. 231Th 0b + ? -1
3. 208Tl 0b + ? -1
85 834He2
90
231Pa91
208Pb 8281
Nuclear Reactions
• Two types:– Fission = the splitting of nuclei– Fusion = the joining of nuclei (they fuse
together)• Both reactions involve extremely large
amounts of energy
Albert Einstein’s equation E = mc2 illustrates the energy found in even small amounts of matter
Nuclear Fission:
• Is the splitting of one heavy nucleus into two or more smaller nuclei, as well as some sub-atomic particles and energy.
• A heavy nucleus is usually unstable, due to many positive protons pushing apart.
• When fission occurs:1.Energy is produced.2.More neutrons are given off.
Nuclear Fission
• Neutrons are used to make nuclei unstable– It is much easier to crash a neutral neutron than a positive proton
into a nucleus to release energy.
Nuclear FissionComplete the following nuclear equations:
(a) 238U + 1n 239U + ?
(b) 9Be + 1H 6Li + ?
(c) 9Be + 4He 12C + ?
Nuclear Fusion
• joining of two light nuclei into one heavier nucleus.– In the core of the Sun, two
hydrogen nuclei join under tremendous heat and pressure to form a helium nucleus.
– When the helium atom is formed, huge amounts of energy are released.
The fusion of hydrogen nuclei
• Scientists cannot yet find a safe, and manageable method to harness the energy of nuclear fusion.– “cold fusion” would occur at temperatures and
pressures that could be controlled (but we haven’t figured out how to get it to happen)
Complete the following nuclear equations, thought to be the source of the energy of some stars.(a) 1H + 12C ?(b) 13N 13C + ?(c) 13C + 1H ?(d) 1H + 14N ?(e) 15O 15N + ?(f) 15N + 1H 12C + ?
Nuclear Fusion
Applications
• Medicine – Chemotherapy – Power pacemakers– Diagnostic tracers
• Agriculture– Irradiate food– Pesticide
• Energy – Fission– Fusion
X-ray examination of luggage at a security station.
© 2003 John Wiley and Sons Publishers
Courtesy Robert Maass/Corbis Images
Food Irradiation
•Food can be irradiated with g rays from 60Co or 137Cs.•Irradiated milk has a shelf life of 3 mo. without refrigeration.•USDA has approved irradiation of meats and eggs.
An image of a thyroid gland obtained through the use of radioactive iodine.
© 2003 John Wiley and Sons Publishers
Courtesy Custom Medical Stock Photo
Images of human lungs obtained from a γ-ray scan.
© 2003 John Wiley and Sons Publishers
Courtesy CNRI/Phototake
A cancer patient receiving radiation therapy.
© 2003 John Wiley and Sons Publishers
Courtesy Kelley Culpepper/Transparencies, Inc.
The world’s first atomic explosion, July 16, 1945 at Alamogordo, New Mexico.
© 2003 John Wiley and Sons Publishers
Courtesy Scott Camazine/Photo Researchers
Remains of a building after the explosion of the uranium bomb at Hiroshima, August 6, 1945.
© 2003 John Wiley and Sons Publishers
Courtesy Shigeo Hayashi
Cooling towers of a nuclear power plant.
© 2003 John Wiley and Sons Publishers
Courtesy David Bartruff/Corbis Images
The nuclear power plant at Chernobyl, after the accident of April 16, 1986.
© 2003 John Wiley and Sons Publishers
Courtesy Sipa Press
• Hazardous wastes produced by nuclear reactions are problematic.– Some waste products, like fuel rods, can be re-used– Some products are very radioactive, and must be
stored away from living things.• Most of this waste is buried underground, or stored in
concrete• It takes 20 half-lives (thousands of years) before the
material is safe.
Challenges of Nuclear Power
»Disposal of waste products
Construction of a tunnel that will be used for burial of radioactive wastes deep within Yucca Mountain, Nevada.
© 2003 John Wiley and Sons Publishers
Courtesy Yucca Mountain Project
Disposal of radioactive wastes by burial in a shallow pit.
© 2003 John Wiley and Sons Publishers
Courtesy Matthew Neal McVay/Stone/Getty Images