Transcript Nuclear Chemistry

N UCLEAR C HEMISTRY
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C HEMICAL VS N UCLEAR
R EACTIONS
N UCLEAR S YMBOLS
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Mass Number
Atomic Number
A
ZX
Element Symbol
D ECAY PARTICLES

Alpha(α) Particle

2 protons and 2 neutrons

Helium nucleus
4He
2

or 42a
Gamma(γ) Particle

Energy that accompanies a decay reaction
0
0
γ
D ECAY PARTICLES

Beta(β) Particles

electron
0e
or -10b
0e
or +10b
-1

Positron
+1
O THER PARTICLES

Proton
1p
1

or
Neutron
1n
0
1H
1
B ALANCING N UCLEAR E QUATIONS
1. Conserve mass number (A).
2. Conserve atomic number (Z) or nuclear charge.
P RACTICE P ROBLEM
212Po
decays by alpha emission.
212Po
+
84
212Po
84
4He
2
+ 208Pb
82
In radioactive decay steps, the beginning radioactive isotope
is called the parent and the product is called the daughter.
D ECAY E XAMPLES
Beta decay
14C
6
14N
7
+-10b + n
11B
5
++10b + n
Positron decay
11C
6
Electron capture decay
37
18 Ar
+ -10e
37Cl
17
+n
Alpha decay
212Po
84
4He
2
+ 208
82Pb
N UCLEAR T RANSMUTATION
Bombarding an element with
particles to produce new elements
14N
7
27
13 Al
+ 24a
+ 24a
17O
8
+ 11p
30P
15
+ 01n
Cyclotron Particle Accelerator
14N
7
+ 11p
11C
6
+ 42a
U RANIUM D ECAY S ERIES
n/p too large
beta decay
X
Y
n/p too small
positron decay or electron capture
N UCLEAR S TABILITY
•
Certain numbers of neutrons and protons are extra stable
•
n or p = 2, 8, 20, 50, 82 and 126
•
Like extra stable numbers of electrons in noble gases
(e- = 2, 10, 18, 36, 54 and 86)
•
Nuclei with even numbers of both protons and neutrons
are more stable than those with odd numbers of neutron
and protons
•
All isotopes of the elements with atomic numbers higher
than 83 are radioactive
•
All isotopes of Tc and Pm are radioactive
H ALF L IFE
H ALF -L IFE

Time required for half a sample to decay

The stability of the isotope is what
determines the rate of decay.
Less Stable = Faster Decay
H ALF -L IFE
After each half-life, half of
the sample decays.
 Start = 100%
 40 blue particles are
present
 1 half-life = 50%
 20 blue remain
 2 half-lives = 25%
 10 blue remain
 3 half-lives = 12.5%
 5 blue remain
 4 half-lives = 6.25%
 2.5 blue remain

Amount never
becomes zero!!
H ALF -L IFE

After 10 half-lives sample considered
nonradioactive because it approaches the
level of background radiation.

Because the amount never reaches zero,
radioactive waste disposal and storage causes
problems.

Would you want radioactive waste stored in
your community?

How can we get rid of nuclear radioactive
waste?
H ALF L IFE P RACTICE

Example 1:
The half-life of mercury-195 is 31 hours. If you
start with a sample of 5.00 g, how much of it
will still be left after 93 hours?
H ALF L IFE P RACTICE C ONT

Example 2:
How many half lives have passed if there is
only 1.875 g left of a 30 g sample?
If the half life for this sample is 1 hour, how
many total hours have gone by?
N UCLEAR S TABILITY
N UCLEAR B INDING E NERGY
Nuclear binding energy (BE):
energy required to break up a nucleus into its component
protons and neutrons.
Einstein’s energy mass relationship:
E = mc2
Links energy and mass calculations
N UCLEAR BINDING ENERGY PER
NUCLEON VS M ASS NUMBER
nuclear binding energy
nucleon
nuclear stability
N UCLEAR F USION

Combining of small nuclei to form larger ones

Occurs in stars at high temperatures

Called a thermonuclear reaction
N UCLEAR F ISSION

Breaking down of a large massive atom into
smaller ones

Nuclear chain reaction: self-sustaining
sequence of nuclear fission reactions.
Ping Pong Video

critical mass: minimum mass of fissionable
material required to generate a self-sustaining
nuclear chain reaction
T WO T YPES
Non-critical
“controlled”
OF
F ISSION
Super Critical
C ONTROLLED N UCLEAR F ISSION
Schematic
diagram of a
nuclear
fission reactor
G EIGER -M ÜLLER C OUNTER
Used to measure level of Radioactivity