Nuclear Chemistry

•The study of the structure of atomic nuclei and the changes they undergo.

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

Figure 4.1

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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.

Figure 4.2: The penetrating power of radiation.

© 2003 John Wiley and Sons Publishers

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,

Figure 4.4: The components of α rays, β rays, and γ rays.

© 2003 John Wiley and Sons Publishers

Types of radioactive decay

• alpha particle emission– loss of a helium

nucleus.

Beta decay, Nuclear changes that accompany the emission of a beta particle.

Types of radioactive decay

epn 01

11

10

b particle emission

• 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 + ?

Fission produces a chain reaction

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.

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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.

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Courtesy Custom Medical Stock Photo

Images of human lungs obtained from a γ-ray scan.

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Courtesy CNRI/Phototake

A cancer patient receiving radiation therapy.

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Courtesy Kelley Culpepper/Transparencies, Inc.

The world’s first atomic explosion, July 16, 1945 at Alamogordo, New Mexico.

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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.

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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

Challenges of Nuclear Power

• Disposal of waste products

• 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.

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Courtesy Yucca Mountain Project

Disposal of radioactive wastes by burial in a shallow pit.

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Courtesy Matthew Neal McVay/Stone/Getty Images

Albert Einstein, he discovered the equation that relates mass and energy.

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Courtesy AP/Wide World Photos