NUCLEAR CHEMISTRY

Unit 2.5

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

Bonds are broken

Nuclei emit particles and/or rays

Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Bonds are broken Nuclei emit particles and/or rays

Atoms are rearranged

Atoms changed into atoms of another element

Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Bonds are broken Nuclei emit particles and/or rays

Atoms may be rearranged Atoms changed to atoms of different element

Involve valence electrons

Involve protons, neutrons, and/or electrons

Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Bonds are broken Nuclei emit particles and/or rays

Atoms are rearranged Atoms change into atoms of different element

Involve valence electrons Involve protons, neutrons, and/or electrons

Small energy changes

Large energy changes

Chemical vs. Nuclear Reactions

Chemical Reactions Nuclear Reactions

Bonds are broken Nuclei emit particles and/or rays

Atoms are rearranged Atoms change into atoms of different element

Involve valence electrons Involve protons, neutrons, and/or electrons

Small energy changes Large energy changes

Reaction rate can be changed.

Reaction rate cannot be changed

The Discovery of Radioactivity (1895 – 1898):

found that invisible rays were emitted when electrons hit the surface of a fluorosent screen (discovered x-rays)

Becquerel accidently discovered that phosphorescent rock produced spots on photographic plates

Roentgen

uranium

The Discovery of Radioactivity (1895 – 1898):

isolated the components (

atoms) emitting the rays – process by

which atoms give off – the penetrating

rays and particles by a radioactive source

Marie and Pierre Curieuranium

Radioactivityrays or particlesRadiation

emitted

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 Curie, continued

The Discovery of Radioactivity (1895 – 1898):

– atoms of the same element with different numbers of – isotopes of atoms with unstable nuclei

(too many or too few neutrons) – when

unstable nuclei lose energy by emitting to become more

IsotopesneutronsRadioisotopes

Radioactive decayradiationstable

Spontaneous Reaction!

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

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Beta radiation

Composition – Beta particles, same as an electron

Symbol – e-, 0-1β

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 – ooγ

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

body easily) Shielding – lead, concrete

Review of Atomic Structure

Nucleus Electron Cloud

99.9% of the mass1/10,000 the size of the atom

0.01% of the mass 9,999 times the size of the nucleus

Review of Atomic Structure

Nucleus Electron Cloud

99.9% of the mass1/10,000 the size of the atom

0.01% of the mass, 9,999 times the size of the nucleus

Protons (p+) and neutrons (n0)

Electrons (e-)

Review of Atomic Structure

Nucleus Electrons

99.9% of the mass1/10,000 the size of the atom

0.01% of the mass, 9,999 times the size of the nucleus

Protons (p+) and neutrons (n0) Electrons (e-)

Positively charged

Negatively charged

Review of Atomic Structure

Nucleus Electrons

99.9% of the mass1/10,000 the size of the atom

0.01% of the mass, 9,999 times the size of the nucleus

Protons (p+) and neutrons (n0) Electrons (e-)

Positively charged Negatively charged

Strong nuclear force (holds the protons together)

Weak electrostatic force (between electrons and nucleus

Chemical Symbols

A chemical symbol looks like…

p+ = e- = atomic #

To find the number of , subtract the

from the

C6

14

mass #

atomic #

mass #atomic #neutrons

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

notdecompose

201very stable1:1 p+:n0

6 6

Nuclear Stability

Elements with atomic #s to are .

ratio of protons:neutrons (p+ : n0) Example: Mercury – 200 has

protons and neutrons

2183marginally stable

1:1.512080

Nuclear Stability

Elements with atomic #s are and . Examples: and

> 83radioactive

unstable

PlutoniumUranium

Alpha Decay

Alpha decay – emission of an alpha particle ( ), denoted by the symbol , because an α 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 .

α42He

4mass

+2 protonsatomic

Atomic number balanced2

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.

210Po84

Mass #

Atomic #

Step 2: Draw the arrow.Step 3: Write the alpha particle.Step 4: Determine the other product (ensuring everything is balanced).

4He2 206Pb82

Alpha Decay

Example 2: Write the nuclear equation for the radioactive decay of radium – 226 by alpha emission.

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

226Ra88

Mass #

Atomic #

Step 2: Draw the arrow.Step 3: Write the alpha particle.Step 4: Determine the other product (ensuring everything is balanced).

4He2 222Rn86

Beta decay

Beta decay – emission of a beta particle ( ), a fast moving , denoted by the symbol or . β has insignificant mass ( ) and the charge is because it’s an .

Beta decay causes change in number and causes the number to increase by .

A neutron is converted to a proton and a beta particle.

β0

electron-1

no mass1atomic

electron e-e0-1

Beta Decay

Example 1: Write the nuclear equation for the radioactive decay of carbon – 14 by beta emission.

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

14 C6

Mass #

Atomic #

Step 2: Draw the arrow.Step 3: Write the beta particle.Step 4: Determine the other product (ensuring everything is balanced).

0e-1 14N7

Beta Decay

Example 2: Write the nuclear equation for the radioactive decay of zirconium – 97 by beta decay.

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

97Zr40

Mass #

Atomic #

Step 2: Draw the arrow.Step 3: Write the beta particle.Step 4: Determine the other product (ensuring everything is balanced).

0e-1 97Nb41

Gamma decay

Gamma rays – high-energy radiation, denoted by the symbol .

γ 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 mass number or atomic number, they are usually from nuclear equations.

electromagneticγ

0 0no mass atomic

alwaysno

omitted

Transmutation

the of an atom of one element to an atom of a different element.

Radioactive decay is one way that this occurs!

Transmutationconversion

Review

Type of Radioact

ive Decay

Particle

Emitted

Change in Mass

#

Change in

Atomic #

Alpha α He

-4 -2

Beta β e 0 +1Gamma γ 0 0

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0-1

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: 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? ______________

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? ______________

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? ______________

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.

Nuclear Reactions

Characteristics: Isotopes of one element are

into isotopes of another element Contents of the change amounts of are

released

changednucleus

Large energy

Types of Nuclear Reactions

decay – alpha and beta particles and gamma ray emission

Nuclear - emission of a or

Radioactivedisintegration

neutronproton

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).

Fissionsplitting

slowlysplit

Chainequal

two

nuclear reactorsspeeddeabsorbing

Nuclear Fission

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

- Examples – atomic bomb, current nuclear power plants

Nuclear Fission

Disadvantages Produces high level radioactive waste that

must be stored for 10,000’s of years. Meltdown causes disasters like in Japan and

Chernobyl.

Advantages Zero air pollution Not a fossil fuel so doesn’t contribute to

climate change

Nuclear Fusion

- Fusion: Combining of two nuclei - Two light nuclei combine to form a single

heavier nucleus - Does not occur under standard conditions

(positive nuclei repel each other) - Advantages compared to fission – No

radioactive waste, inexpensive ,

- Disadvantages - requires large amount of energy to start, difficult to control.

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

Uses of Radiation

Radioactive dating: Carbon–14 used to determine the age of an object that was once alive.

Detection of diseases: Iodine–131 used to detect thyroid problems, technetium–99 used to detect cancerous tumors and brain disorders, phosphorus – 32 used to detect stomach cancer.

Treatment of some malignant tumors (cobalt–60 and cesium–137) cancer cells are more sensitive to radiation than normal, healthy cells

Uses of Radiation

X-rays Radioactive tracers: used in research

to tag chemicals to follow in living organisms

Everyday items: thorium–232 used in lantern mantels, plutonium–238 used in long-lasting batteries for space, and americium–241 in smoke detectors.