NUCLEAR CHEMISTRY. Introduction to Nuclear Chemistry Nuclear chemistry is the study of the...

NUCLEAR CHEMISTRY

Introduction to Nuclear Chemistry

Nuclear chemistry is the study of the structure of and the they undergo.

atomic nuclei changes

Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Occur when bonds are broken

Occur when nuclei emit particles and/or rays

Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Occur when bonds are broken Occur when nuclei emit particles and/or rays

Atoms remain unchanged, although they may be rearranged

Atoms often converted into atoms of another element

Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Occur when bonds are broken Occur when nuclei emit particles and/or rays

Atoms remain unchanged, although they may be rearranged

Atoms often converted into atoms of another element

Involve only valence electrons

May involve protons, neutrons, and electrons

Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Occur when bonds are broken Occur when nuclei emit particles and/or rays

Atoms remain unchanged, although they may be rearranged

Atoms often converted into atoms of another element

Involve only valence electrons May involve protons, neutrons, and electrons

Associated with small energy changes

Associated with large energy changes

Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Occur when bonds are broken Occur when nuclei emit particles and/or rays

Atoms remain unchanged, although they may be rearranged

Atoms often converted into atoms of another element

Involve only valence electrons May involve protons, neutrons, and electrons

Associated with small energy changes

Associated with large energy changes

Reaction rate influenced by temperature, particle size, concentration, etc.

Reaction rate is not influenced by temperature, particle size, concentration, etc.

The Discovery of Radioactivity (1895 – 1898):

found that invisible rays were emitted when electrons bombarded the surface of certain materials.

Becquerel accidently discovered that phosphorescent salts produced spontaneous emissions that darkened photographic plates

Roentgen

uranium

Antoine Henri Becquierel

Radioactive decay

Discovered by Antoine Henri Becquerel in 1896

He saw that photographic plates developed bright spots when exposed to uranium metals

Radioactive Decay – nucleus decays spontaneously giving off an energetic particle

The Discovery of Radioactivity (1895 – 1898):

isolated the components ( atoms) emitting the rays

– process by which particles give off

– the penetrating rays and particles by a radioactive source

Marie Curieuranium

Radioactivityrays

Radiationemitted

The Discovery of Radioactivity (1895 – 1898):

identified 2 new elements, and on the basis of their radioactivity

These findings Dalton’s theory of indivisible atoms.

poloniumradium

contradicted

Marie Sklodowska Curie with her daughter, Irene.

The Discovery of Radioactivity (1895 – 1898):

– atoms of the element with different numbers of

– isotopes of atoms with nuclei (too / neutrons)

– when unstable nuclei energy by emitting to attain more atomic configurations ( process)

Isotopes sameneutrons

Radioisotopesunstable fewmanyRadioactive decay

radiationlosestable

spontaneous

Alpha radiation

Composition – Alpha particles, same as helium nuclei

Symbol – Helium nuclei, He, α Charge – 2+ Mass (amu) – 4 Approximate energy – 5 MeV Penetrating power – low (0.05 mm body

tissue) Shielding – paper, clothing

42

Beta radiation

Composition – Beta particles, same as an electron

Symbol – e-, β Charge – 1- Mass (amu) – 1/1837 (practically 0) Approximate energy – 0.05 – 1 MeV Penetrating power – moderate (4 mm

body tissue) Shielding – metal foil

Gamma radiation

Composition – High-energy electromagnetic radiation

Symbol – γ Charge – 0 Mass (amu) – 0 Approximate energy – 1 MeV Penetrating power – high (penetrates

body easily) Shielding – lead, concrete

Ionizing power and penetrating power: an analogy.

Types of radioactive decay alpha particle emission beta emission positron emission electron capture gamma emission

Alpha emission

Beta Particle emisson

epn 01

11

10

Review

Type of Radioact

ive Decay

Particle

Emitted

Change in Mass

#

Change in

Atomic #

Alpha α He -4 -2Beta β e 0 +1

Gamma γ 0 0

42

0-1

Chemical Symbols

A chemical symbol looks like…

To find the number of , subtract the

from the

C6

14

mass #

atomic #

mass #atomic #

neutrons

Half-Life

is the required for of a radioisotope’s nuclei to decay into its products.

For any radioisotope,# of ½ lives % Remaining

0 100%

1 50%

2 25%

3 12.5%

4 6.25%

5 3.125%

6 1.5625%

Half-life time half

Half-Life

0 1 2 3 4 5 6 70

10

20

30

40

50

60

70

80

90

100

Half-Life

# of Half-Lives

% R

em

ain

ing

Half-Life

For example, suppose you have 10.0 grams of strontium – 90, which has a half life of 29 years. How much will be remaining after x number of years?  

You can use a table:

# of ½ lives

Time (Years)

Amount Remaining (g)

0 0 10

1 29 5

2 58 2.5

3 87 1.25

4 116 0.625

Half-Life

Or an equation!

mt = m0 x (0.5)n

mass remaining

initial mass

# of half-lives

Half-Life

Example 1: If gallium – 68 has a half-life of 68.3 minutes, how much of a 160.0 mg sample is left after 1 half life? ________ 2 half lives? __________ 3 half lives? __________

Half-Life

Example 2: Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days? ______________

Nuclear Fission

- of a nucleus - Very heavy nucleus is split into

approximately fragments - reaction releases several

neutrons which more nuclei - If controlled, energy is released

(like in ) Reaction control depends on reducing the of the neutrons (increases the reaction rate) and

extra neutrons ( creases the reaction rate).

Fission splitting

slowlysplit

Chainequal

two

Nuclear reactorsspeed

deabsorbing

Nuclear Fission

- 1st controlled nuclear reaction in December 1942. 1st uncontrolled nuclear explosion occurred July 1945.

- Examples – atomic bomb, current nuclear power plants

Cooling towers of a nuclear power plant.

© 2003 John Wiley and Sons Publishers

Courtesy David Bartruff/Corbis Images

Construction of a tunnel that will be used for burial of radioactive wastes deep within Yucca Mountain, Nevada.

Disposal of radioactive wastes by burial in a shallow pit.

Nuclear Fusion

- of a nuclei - Two nuclei combine to form a

heavier nucleus - Does not occur under standard conditions

( repels ) - Advantages compared to fission -

,

- Disadvantages - requires amount of energy to , difficult to

- Examples – energy output of stars, hydrogen bomb, future nuclear power plants

lightcombiningFusion

+ +

start

noradioactivewasteinexpensive

largecontrol

single

Applications

Medicine Chemotherapy Power pacemakersDiagnostic tracers

AgricultureIrradiate foodPesticide

Energy FissionFusion

X-ray examination of luggage at a security station.

An image of a thyroid gland obtained through the use of radioactive iodine

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

A cancer patient receiving radiation therapy.