nuclear chemistry unit 16. introduction to nuclear chemistry nuclear chemistry is the study of the...
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NUCLEAR CHEMISTRY
Unit 16
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
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
RadioactivityraysRadiation
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
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 sameneutronsRadioisotopesunstable fewmany
Radioactive decayradiationlosestablespontaneous
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
Review of Atomic Structure
Nucleus Electrons
99.9% of the mass1/10,000 the size of the atom
0.01% of the mass
Review of Atomic Structure
Nucleus Electrons
99.9% of the mass1/10,000 the size of the atom
0.01% of the mass
Composed of protons (p+) and neutrons (n0)
Composed of 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
Composed of protons (p+) and neutrons (n0)
Composed of 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
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
Chemical Symbols
A chemical symbol looks like…
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
2182marginally stable
1:1.512080
Nuclear Stability
Elements with atomic #s are
and . Examples: and
> 82radioactive
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 .
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 one atom of one element to an atom of a different element ( decay is one way that this occurs!)
Transmutationconversion
radioactive
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 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
+ +
startno radioactive waste
inexpensive
largecontrol
single
Uses of Radiation
Radioactive _______________ - Carbon - ____ used to determine the ________ of an object that was once alive.
___________________________ of diseases – Iodine – 131 used to detect _________________ problems, technetium – 99 used to detect ___________ tumors and ____________ disorders, phosphorus – 32 used to detect __________ cancer.
Treatment of some _______________________ (cobalt – 60 and cesium – 137) – cancer cells are more ________________________ to radiation than normal, healthy cells
Uses of Radiation
X-rays Radioactive ________________ (used in
research to _______ chemicals) Everyday items – thorium – 232 used in
______________________, plutonium – 238 used in _______________________, and americium – 241 in ___________________________________