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Chemistry 100

Bettelheim, Brown, Campbell & FarrellNinth Edition

Introduction to General,

Organic and Biochemistry

Chapter 9

Nuclear Chemistry

Electromagnetic Radiation•All electromagnetic radiation consists of waves.

•All waves travel at the same velocity in a vacuum, 3.0 x 108 m/s.

•The only difference between forms of electromagnetic radiation is the wavelength, λ.

•Frequency, ν: the number of crests that pass a given point in a second.

•The higher the frequency, the shorter the wavelength.

•The higher the frequency, the higher the energy.

•Our eyes are sensitive to only a small part of the electromagnetic spectrum.

Radioactivity

Spontaneous Nuclear DecayAlpha - α He2+

24 A Helium Cation ejected from .

the nucleus at high energy.

Beta - β 0-1e An electron ejected from

the nucleus at high energy. .

Gamma - γ γ00 High Energy electromagnetic .

radiation.

Reduces mass of emitting nucleus, drops atomic number.

Mass of emitting nucleus unchanged, increases atomic number.

Mass/atomic number unchanged, reduces energy of emitting nucleus, usually accompanies beta emission.

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Radioactivity

Other Types of Nuclear Decay

Beta(+) - β+ 0+1e An anti-electron ejected from .

the nucleus at high energy.

Positron emission:

Beta(+) - β+ n10p1

10

+1e+

Beta decay - β 0-1en1

0 p11 +

Electron Capture - ec - A nucleus captures an .electron from outside.

0-1e n1

0p11 +

Nuclear Symbols

U23592

Isotope Number#n + #p = At. mass~

Atomic Number= #p

Atomic Symbol

= nuclear charge

Elementary Particles: p11He2+

24 H1

1; or

0+1en1

0 γ00

0-1e; ; ;or0

-1β β0+1 or

Balancing Nuclear Equations

Can you balance these? The subscript numbers and the superscript numbers must be algebraically equal on each side of the arrow.

Alpha decay: Ra He 2+24+226

88

Beta(+) decay: 0+1 e+Tc95

43

Beta(-) decay: 0-1 e+C6

14

Electron Capture + 0-1e40

19 K

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Transmutation of ElementsNuclear Bombardment: .

He2+24 H11N14

7 + +

n10Be9

4 + +He2+24

N147 + +n1

0 H11Supply the missing nuclides!

Neutrons are better particles to bombard the nucleus! Why?

Nuclear ReactionsNuclear Fission:

n10n1

0 + + +U23592 Kr94

36 3

Nuclear Fusion:

n10+ +H2

131H

Tritium "T"

Deuterium "D"

Determine the missing Nuclide!

Radiocarbon Dating

N147 C14

6+ +n10 H1

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The half-life of Carbon-14 is 5,730 years.

Constant Carbon-14 levels maintained by:

Constant levels of nitrogen atoms in the atmosphere as N2.

Constant levels of high energy neutrons from the sun.

Based on the near constant levels of Carbon-14 in the Earth’s atmosphere formed by the reaction:

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Biological Effects of Radiation•All Radiation causes ionization. In tissues this results in the formation of peroxide free-radicals.

•Although alpha particles cause more damage than x-rays or gamma radiation, they have very low penetrating power and cannot pass through skin.

•Consequently alpha particles are not harmful to humans or animals as long as they do not get into the body; if they do getinto the body, they can be quite harmful.

•Beta particles are less damaging to tissue than alpha particles but penetrate farther and so are generally more harmful.

•Gamma rays, which can easily penetrate skin, are by far the most dangerous and harmful form of radiation.

•Becquerel (Bq): one Bq is 1 disintegration/s.

•Curie (Ci): one Ci = 3.7 x 1010 Bq.

•Roentgen (R): the amount of radiation that produces ions having 2.58 x 10-4 coulomb/kg.

•Radiation absorbed dose (Rad): an ionizing radiation unit; the SI unit is the Gray (Gy). 1 rad = 0.01 Gy

•Gray (Gy): one Gy = 1 joule/kilogram (1 J/kg).

•Roentgen-equivalent-man (Rem): a measure of the effect of the radiation when one roentgen is absorbed by a person; the SI unit is the Sievert (Sv) where one Sv = 1 J/kg. 1 rem = 0.01 Sv.

Radiation Dosimetry (Terms & Units)

•A single whole-body irradiation of 25 rem is noticeable in blood count. 1 rem = 1000 millirem.

•A single dose of 100 rem causes typical symptoms of radiation sickness.

•A single dose of 400 rem causes death within one month in 50% of the exposed persons.

•A single dose of 600 rem is almost invariably lethal within a month.

•It is estimated that a single dose of 50,000 rem is needed to kill bacteria, and up to 106 rem is needed to inactivate viruses.

Radiation Dosimetry

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