Transcript THERMAL ENERGY

Chapters 18
NUCLEAR
CHEMISTRY
1
CHAPTER OUTLINE







Atomic Structure
Radioactivity
Alpha Decay
Beta & Gamma Decays
Radionuclide
Half Life
Nuclear Fission & Fusion
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ATOMIC
STRUCTURE
 The general designation for an atom is shown
below:
No. of
protons
No. of protons
& neutrons
# of e = # of p+ (neutral)
# of n0 = A - Z
3
Example 1:
Determine the number of protons, electrons and
neutrons in a fluorine atom .
19
9
F
# of protons = atomic no. (Z)= 9
A = 19 # of electrons = # of protons = 9
Z=9
# of neutrons = A-Z = 19-9 = 10
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Example 2:
Argon (Ar) has 18 protons, 18 electrons and 22
neutrons. Write a formula designation for an
argon atom.
40
18
Ar
Atomic no. = # of protons = 18
Mass no. = p+ + n0 = 18 + 22 = 40
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HISTORY OF
RADIOACTIVITY




The discovery of radioactivity can be
attributed to several scientists.
Wilhem Roentgen discovered X-rays in 1895.
Shortly after that, Henri Becquerel observed
radioactive behavior while experimenting
with salts of uranium.
However, the term radioactivity was first
coined by Marie Curie in 1898.
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RADIOACTIVITY



Radioactivity is the spontaneous emission of
particles and/or rays from the nucleus of an
atom.
Nuclides are said to be stable (non-radioactive)
or unstable (radioactive).
All elements having an atomic number greater
than 83 (bismuth) have unstable nuclei, which
undergo spontaneous decay (disintegration),
and are therefore radioactive.
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RADIOACTIVITY


These elements can undergo one of 3 different
kinds of decay called  (alpha),  (beta) and 
(gamma).
When decaying, the original nucleus (A)
changes into another nucleus (B) and gives off
radiation (b).
A ¾¾
® B + b
Parent
Daughter
Radiation
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TYPES OF
RADIATION

γ-Radiations
The
β-Radiations
three different
carry
akinds
charge
of radiations
and
charge
areand
and
attracted
canare
are
be
-Radiations
carry no
a negative
positive
charge
distinguished
attracted
to
neitherto
plate.
the
bypositive
negative
their interactions
plate.
plate.
with an
electric field.
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TYPES OF
RADIATION


The
three
different
have
kinds
energy
ofenergy
and
radiations
becan
havebe
 α-Particles
β-Particles
γ-Rays
have
have
highlow
moderate
energy
and
cancan
only
and
be
blocked
different
energies
aa thin
and
penetration
of
blocked by
by
thin sheet
thick
sheet
sheet
ofofpaper.
metal.
lead. abilities.
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ALPHA DECAY
 Note
Alphathat
decay
theoccurs
sum ofwhen
the atomic
a nucleus
numbers
changes
and
Loss of alpha particle from the nucleus results in loss
the
numbers
onand
the gives
left and
right side
intomass
another
nucleus
offthe
an -particle,
of 4 in mass number (A) and 2 in4 atomic number (Z).
which
of
the equation
is a helium
arenucleus
equal. ( He).
2
Th ¾ ¾
®
232
90
228
88
4
2
Ra + He
232
90 = 228
88 ++24
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Examples:
1.
238
92
U undergoes alpha decay. Write the
equation for this process.
238
92
U ¾¾
® ??? + He
234
90
U ¾¾
®
23892 – 2 = 90
92
4
2
234
90
4
2
Th + He
238 – 4 = 234
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Examples:
2. Write the equation for alpha decay of
radium isotope 226
88 Ra .
226
88
Ra ¾ ¾
® ??? + He
222
86
Ra ¾ ¾
®
226
88 – 2 = 86
88
222
86
4
2
4
2
Rn + He
226 – 4 = 222
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BETA DECAY
 Beta
In beta
decay
decay,
occurs
a neutron
when aisnucleus
transformed
changes
into
a proton
into another
and an electron.
nucleus and
The
gives
0
off a ß-particle,
proton
remains in
which
the nucleus,
is an electron
while(the
-1e).
electron is emitted as a beta particle.
14
6
C ¾¾
®
1
0
n ¾¾
®
14
7
146==14
7 -1
+0 1
1
0
-1
N+ e
0
-1
p+ e
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GAMMA
DECAY
 Gamma decay occurs when a nucleus
gives off -rays , and becomes a less
energetic form of the same nucleus.
204
82
Pb ¾ ¾
®
*
More energetic
204
82
Pb + γ
Less energetic
gamma
radiation
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Examples:
1. Complete the following equation for
nuclear decay:
46
21
* γ-decay
Sc ¾ ¾
® ??? + ???
Sc
®
Sc ++ γ
Sc ¾¾¾
¾
® ???
46
46
21
21
**
46
21
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Examples:
2. Complete the following equation for
nuclear decay:
47
21
β-decay
Sc ¾ ¾
® ??? + ???
4747
00
¾
® 22???
ScSc¾¾¾
®
22Ti ++-1-1ee
47 47
21 21
47
21==47
22+-10
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POSITRON
DECAY
 Certain nuclear processes can also lead
to a fourth form of radiation, called a
0
positron ( +1e).
17
9
F ¾¾
®
17
9 == 817+ +1 0
17
8
O+
0
+1
e
positron
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REVIEW: TYPES OF
RADIATION

Alpha () particle
is two protons and two neutrons

Beta () particle
is a high-energy electron

Positron (+)
is a positive electron

Gamma ( ) ray
is high-energy released from a nucleus
General, Organic, and Biological Chemistry
Pearson Education, Inc.
Copyright © 2010
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SUMMARY OF TYPES OF
RADIATION
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General, Organic, and Biological Chemistry
RADIONUCLIDES
 A nuclide will be radioactive if it meets
any of the following criteria:
1. Its atomic number is greater than 83.
2. It has fewer n0 than p+ in the nucleus.
Exceptions: 11 H ;
3
2
He
3. It has odd # of n0 and odd # of p+.
2
1
6
3
Exceptions: H ; Li ;
10
5
B;
14
7
N
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Examples:
Which is the radionuclide in each of the
following pairs:
1)
208
82
2)
19
10
3)
63
29
Pb and
Ne and
Cu and
222
86
Rn
20
10
64
29
Ne
Cu
Z > 83
n0 < p+
p+ and n0 are odd
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SMOKE
DETECTORS
 A
Inpractical
these detectors,
use of radionuclides
a radionuclideisdecays
their
useform
to
in some
α–particles.
smoke detectors.
 When
The α–particles
smoke
ionize (charge)
particles
interfere
the
air particles
with
the ions,and
keep a current
current
is reduced
running
in
the circuit,
through
and a
the circuit.
alarm
goes off.
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HALF-LIFE
The half-life of a radioisotope is the
time for the radiation level to
decrease (decay) to one-half of the
original value.
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General, Organic, and Biological Chemistry
DECAY CURVE
A decay curve shows the decay of
radioactive atoms and the remaining
radioactive sample.
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General, Organic, and Biological Chemistry
DECAY CURVE
 Each half-life reduces
the amount of radionuclide to half of the
previous amount.
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Example 1:
Iodine-131 has a half-life of 8 days. What mass of a
40 g sample of iodine-131 will remain after 24 days.
1 half-life
24 days x
= 3 half-lives
8 days
40 g
1st ½ -life
20 g
2nd ½ -life
10 g
3rd ½ -life
5g
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Example 2:
How long would it take for a sample of C-14 to decay
from 20.0 g to 0.625 g? (½- life of C=14 = 5730 y)
½ life
0
1
2
3
4
5
g
20.0
10.0
5.00
2.50
1.25
0.625
5730 y
5 half-lives x
= 28650 y
1 half-life
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NUCLEAR
FISSION
 Fission is the process by which a large nucleus
is “split” into smaller nuclei, with a large
amount of energy released.
1
0
n+ 235
®
92 U ¾ ¾
236
92
U¾ ¾
®
140
54
236
92
U (unstable)
1
Xe+ 94
Sr+2
38
0n
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NUCLEAR FISSION
DIAGRAM AND EQUATION
 A nuclear bomb is an example of an
uncontrolled fission, while a nuclear reactor is
an example of a controlled fission.
1
0
n+
235
92
U
236
92
U 
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Pearson Education, Inc.
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36
Kr +
142
56
1
0
Ba + 3 n + energy
Copyright © 2010
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CHAIN REACTION
A chain reaction
occurs
 when a critical
mass of uranium
undergoes fission
 releasing a large
amount of heat
and energy that
produces an
atomic explosion
General, Organic, and Biological Chemistry
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NUCLEAR POWER PLANTS
In nuclear power plants,
 fission is used to produce energy
 control rods in the reactor absorb
neutrons to slow and control the
chain reactions of fission
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Pearson Education, Inc.
Copyright © 2010
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NUCLEAR FUSION
Nuclear fusion
 occurs at extremely high temperatures
(100 000 000 °C)
 smaller nuclei combine to form larger nuclei
 large amounts of energy are released
 this occurs continuously in the sun and stars
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General, Organic, and Biological Chemistry
NUCLEAR
FUSION

The sun uses fusion to produce a helium
nucleus from 4 hydrogen nuclei, giving off 2
positrons and energy.
4 H¾ ¾
® He + 2 e + energy
1
1
4
2
0
+1
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THE END
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