Ch. 25 Nuclear Chemistry
Nuclear Reactions:
Nuclear Reactions vs. Ordinary Chemical Reactions:
Chemical Reactions:


Involve only the outer electrons of atoms.
Elements do not change from one to another.
Ex. 2H2 + O2  2H2O
Nuclear Reactions:
 Rxn that affects the nucleus
 Unaffected by temperature, pressure, catalysts; can’t be slowed down or
sped up
 Nucleus changes- products can be different elements than the reactants.
Ex.

238
92

234
90ℎ
+ 42
Many nuclei are radioactive
Radioactivity:
 Process by which nuclei emit particles and rays (radiation)
Radiation:
 Penetrating rays and particles emitted by a radioactive source
1. Alpha (α) – stopped by paper, skin, clothing
2. Beta (β)- stopped by metal foil, wood
3. Gamma ()- stopped by lead, thick concrete
Radioisotope:
 An isotope that has an unstable nucleus
 Undergoes radioactive decay – gain stability, releases energy (radiation)
Radioactive decay:

Spontaneous decay of the nucleus into a more stable nucleus

Emits particles +/or radiation
1
Types of Radioactive Decay (Transmutation):

Reactant’s Atomic # and mass # = Product’s atomic # and mass #
Ex. 49 + 42

12
6
+ 10
Atomic # changes = identity of element changes
1. Alpha Emission (α):
 Too many neutrons and protons- gets rid of 2 of each

An alpha particle (
238
U
92
) is emitted.
234
4
Th +
He
90
2
2. Beta Emission (β):
 Too many neutrons – neutron converted into a proton and electron
 A beta particle β (electron) ( −10) is emitted
14
C
6
14
0
N+
e
7
-1
3. Gamma Emission ():
 Emission of electromagnetic energy
 No particles are emitted during gamma radiation
4. Positron Emission (β):
 Too many protons – protons converted into a neutron
 A positron (
0
+1
5. Electron Capture:

e) is emitted
38
K
19
38
0
Ar + e
18
+1
Too many protons, converts a proton to a neutron by capturing an
electron (
0
-1
e)
0
106 Ag +
-1
47
106
Pd
46
2
Artificial Transmutation:
 Particles bombard the nucleus of an atom
 Particle accelerator (Atom Smasher), Nuclear reactors
 Elements above 92 = man-made
ex.
14
4
17
1
7 + 2  8 + 1
238
92
+ 10  239
92 
239
93
+
0
−1
http://www.huffingtonpost.com/2012/07/03/higgs-boson-video_n_1646116.html
http://www.youtube.com/watch?v=RIg1Vh7uPyw&feature=related
Half-Life:
 Time it takes for ½ of the atoms of a radioactive isotope to decay
 More stable isotopes – decay slowly  longer ½ life
 Less stable isotopes- decay quickly  shorter ½ life
Half-Life Table
Nuclide
4
He
2
227
92
U
3
1
H
14
6
C
235
92
U
Half-life
Decay Type
0.802 seconds
Beta-minus
1.3 minutes
Alpha and Gamma
12.3 years
Beta-minus
5730 years
Beta-minus
7.1 x 10
8
years Alpha and Gamma
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Calculating Half-Life:
Ex. 1 Radioactive element has a ½ life of 30 days of an 8 gram sample,
how much will be unchanged after 90 days? How much will be
changed after 90 days?
After: Unchanged
Changed
30 days = 4 grams
(4 grams)
60 days = 2 grams
(6 grams)
90 days = 1 gram
(7 grams)
Ex.2 The following is know about a fossil bone:
a.) Amount of carbon-14 originally in bone = 800g
b.) Amount of carbon-14 presently in bone = 100g
c.) Amount of nitrogen-14 presently in bone = 700g
d.) half-life = 5,730 yrs
How old is the fossil bone?
17,190 yrs
P (C-14)
D (N-14)
Start= 0 yrs
800g
0g
1st = 5,730 yrs
2nd= 11,460 yrs
3rd= 17,190 yrs
400g
200g
100 g
400g
600g
700g
Ex.3 ½ life of radon-222 is 3.824 days. How much of original sample will
be left after 7.648 days?
¼ of original
after 3.824 days = ½ left
after 7.648 days = ½ of the ½ (1/4)
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Comparing Fission & Fusion:
Fission:
 Heavy nuclei are split into lighter nuclei.
 Relatively easy to control but produce radioactive wastes.
 Plutonium and uranium
Fission
Three mile Island
Chernobyl I
Chernobyl II
Fukushima I
Fukushima TIME explanation
Fusion:
 Light nuclei are combined to form heavier nuclei.
 Difficult to initiate and control but produce little radioactive wastes.
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b.) Amount of carbon-14 presently in bone = 100g