nuclear chem 2012

7/28/2019 Nuclear Chem 2012

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NUCLEAR CHEMISTRY

Chapter 25


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Introduction to Nuclear

Chemistry

Nuclear chemistry is the study of the structure

of and

the they undergo.


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Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Occur when bonds

are broken

Occur when nuclei

emit particles

and/or rays


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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


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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


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and/or rays

Atoms remain unchanged, although

they may be rearranged


another element

Involve only valence electrons May involve protons, neutrons, and

electrons

Associated with

small energychanges

Associated with

large energychanges


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

rays

Atoms remain unchanged, although they

may be rearranged


another element

Involve only valence electrons May involve protons, neutrons, andelectrons

Associated with small energy changes Associated with large energy changes

Reaction rate

influenced bytemperature, particle

size, concentration, etc.

Reaction rate is not

influenced bytemperature, particle

size, concentration, etc.


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The Discovery of Radioactivity

(1895 1898):

found that invisible rays were

emitted when electrons bombarded the

surface of certain materials.

Becquerel accidently discovered thatphosphorescent salts produced

spontaneous emissions that darkened

photographic plates


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(1895 1898):

isolated the components (

atoms) emitting the rays

process by which

particles give off

the penetrating rays and

particles by a radioactivesource


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(1895 1898):

identified 2 new elements,

and on the basis of their

radioactivity

These findings Daltonstheory of indivisible atoms.


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(1895 1898):

atoms of the

element with different numbers of

isotopes of atoms

with nuclei (too/ neutrons)

when

unstable nuclei energy by emittingto attain more atomic

configurations ( process)


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Alpha radiation

Composition Alpha particles, same as helium

nuclei

Symbol Helium nuclei, He,

Charge2+

Mass (amu)4

Approximate energy5 MeV

Penetrating powerlow (0.05 mm body tissue)

Shielding paper, clothing

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Beta radiation

Composition Beta particles, same as an

electron

Symbole-,

Charge1-

Mass (amu)1/1837 (practically 0)

Approximate energy0.05 1 MeV

Penetrating powermoderate (4 mm body

tissue)

Shielding metal foil


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Gamma radiation

Composition High-energy electromagnetic

radiation

Symbol

Charge0

Mass (amu)0

Approximate energy1 MeV

Penetrating power high (penetrates body

easily)

Shielding lead, concrete


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Review of Atomic Structure

Nucleus Electrons

99.9% of the mass

1/10,000 the size

of the atom

0.01% of the mass


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Nucleus Electrons

99.9% of the mass

1/10,000 the size of the atom

0.01% of the mass

Composed of

protons (p+) and

neutrons (n0)

Composed of

electrons (e-)


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Nucleus Electrons

99.9% of the mass


0.01% of the mass

Composed of protons (p+) and neutrons (n0) Composed of electrons (e-)

Positively charged Negatively charged


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Nucleus Electrons

99.9% of the mass


0.01% of the mass

Composed of protons (p+) and

neutrons (n0)

Composed of electrons (e-)

Positively charged Negatively charged

Strong nuclear

force (holds the

nucleus together)

Weak electrostatic

force (because

they are charged

negatively


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Chemical Symbols

A chemical symbol looks like

To find the number of , subtract

the

from the

C614


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Nuclear Stability

Isotope is completely stable if the nucleus will

spontaneously .

Elements with atomic #s to are

.

ratio of protons:neutrons ( )

Example: Carbon 12 has protons and

neutrons


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Nuclear Stability

Elements with atomic #s to are

.

ratio of protons:neutrons (p+ : n0)

Example: Mercury 200 has protons and

neutrons


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Nuclear Stability

Elements with atomic #s are

and .

Examples: and


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Alpha Decay

Alpha decay emission of an alpha particle (

), denoted by the symbol , because an

has 2 protons and 2 neutrons, just like the He

nucleus. Charge is because of the 2.

Alpha decay causes the number to

decrease by and the number to

decrease by .

determines the

element. All nuclear equations are

.

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Alpha Decay

Example 1: Write the nuclear equation for the

radioactive decay of polonium 210 by alpha

emission.

Step 1: Write the element that you are starting with.

Mass #

Atomic #

Step 2: Draw the arrow.

Step 3: Write the alpha particle.

Step 4: Determine the other product (ensuringever thin is balanced .


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Alpha Decay


radioactive decay of radium 226 by alpha

emission.

Mass #

Atomic #


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Beta decay

Beta decay emission of a beta particle ( ), a

fast moving , denoted by the

symbol or . has

insignificant mass ( ) and the charge isbecause its an .

Beta decay causes change innumber and causes the number to

increase by .

0

-1


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Beta Decay


radioactive decay of carbon 14 by beta

emission.

Mass #

Atomic #


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Beta Decay


radioactive decay of zirconium 97 by beta

decay.

Mass #

Atomic #


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Gamma decay

Gamma rays high-energy

radiation, denoted by the symbol .

has no mass ( ) and no charge ( ).

Thus, it causes change in or

numbers. Gamma rays almost

accompany alpha and beta radiation.

However, since there is effect on massnumber or atomic number, they are usually

from nuclear equations.


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Transmutation

the of one atom of one

element to an atom of a different element

( decay is one way thatthis occurs!)


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Review

Type of

Radioacti

ve Decay

Particle

Emitted

Change

in Mass #

Change

in Atomic

#

Alpha He -4 -2

Beta e 0 +1

Gamma 0 0

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0-1


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Half-Life

is the required for

of a radioisotopes nuclei to decay into its

products.

For any radioisotope,# of lives % Remaining0 100%

1 50%

2 25%3 12.5%

4 6.25%

5 3.125%

6 1.5625%


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Half-Life

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7

%Remaining

# of Half-Lives

Half-Life


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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 lives Time (Years) AmountRemaining (g)

0 0 10

1 29 52 58 2.5

3 87 1.25

4 116 0.625


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Half-Life

Or an equation!


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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?__________


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Half-Life

Example 2: Cobalt 60, with a half-life of 5

years, is used in cancer radiation treatments.

If a hospital purchases a supply of 30.0 g, how

much would be left after 15 years?______________


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Half-Life

Example 3: 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?______________


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Half-Life

Example 4: The half-life of polonium-218 is 3.0

minutes. If you start with 20.0 g, how long will

it take before only 1.25 g remains?

______________


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Half-Life

Example 5: A sample initially contains 150.0

mg of radon-222. After 11.4 days, the sample

contains 18.75 mg of radon-222. Calculate the

half-life.


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Nuclear Reactions

Characteristics:

Isotopes of one element are

into isotopes of another element

Contents of the change

amounts of are

released


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Types of Nuclear Reactions

decay alpha and beta

particles and gamma ray emission

Nuclear - emission ofa or


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Nuclear Fission

- of a nucleus

- Very heavy nucleus is split intoapproximately fragments

- reaction releases severalneutrons which more nuclei

- If controlled, energy is released

(like in ) Reaction

control depends on reducing the ofthe neutrons (increases the reaction rate) and

extra neutrons ( creasesthe reaction rate).


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Nuclear Fission

- 1st controlled nuclear reaction in December

1942. 1st uncontrolled nuclear explosion

occurred July 1945.

- Examples atomic bomb, current nuclearpower plants


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nuclear chem 2012

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