Transcript Nuclear Chemistry

AP Chemistry
Chapter 23 Notes
Henri Becquerel
ruined some
photographic
plates with x-rays
from a uranium
source and
radioactive decay
was discovered in
1896.
Henri Becquerel’s experiment – (1896)
Tried to see if fluorescent minerals would give off Xrays. Set some out in the sun with covered
photographic film. If minerals gave of X-rays when
they fluoresced, the film should darken – and it did.
Accidentally set some of these minerals in a dark
drawer for a few days with undeveloped film, and was
surprised to see the film strongly exposed. He knew
they gave off X-rays when charged by the sun - but
these results suggested the X-rays were coming from
the mineral itself – Natural Radioactivity – No
external energy source required!
Radioactivity

One of the pieces of evidence for
the fact that atoms are made of
smaller particles came from the
work of Marie Curie (18761934).
 She discovered radioactivity,
the spontaneous disintegration of
some elements into smaller
pieces.
Marie and Pierre Curie’s
experiments with pitchblende –
Discovered Radioactive
Naturally occurring elements,
particularly Uranium, Radium,
and Polonium. Curium was
named after Marie
posthumously
THE GREAT DISCOVERY
W.K. Roentgen’s experiment (1895) Fluorescence –Certain substances will
absorb photons of energy when
exposed to a source (i.e. cathode
rays, the sun), and then emit them
over a period of time – thus they
glow in dark when exposed to UV
light
Cathode rays –beams of electrons
Cathode ray tube (CRT) –Vacuum
tube that has electric current passed
through it .
Component of television sets –that’s
why they call it “the tube”
X-rays –Name given by Roentgen to
unusual stray energy observed to
cause fluorescence across the room
when CRT was used… X-ray because
he did not know what the heck it
was….and the name stuck
BETA PARTICLES
•Consists of – high
speed electron (from
disintegration of
neutron)
•Tissue damage
potential – much
greater than Alpha
•Harmful if ingested?
– not as much as Alpha
•Can be blocked? – by
glass, will penetrate
skin
GOLD FOIL EXPERIMENT
Ernest Rutherford and the Gold Foil Experiment
Disproved Thompson’s plum pudding model
Proved the existence of a nucleus with a positive charge
ALPHA PARTICLES
•Consists of – He
nucleus
•Tissue damage
potential – great – if
internalized
•Harmful if ingested?
– yup, very
•Can be blocked? – by
layer of skin, or
cardboard
•Note that atoms are NOT conserved in
nuclear reactions, but mass numbers and
atomic numbers are.
NUCLEAR RADIATION
Ernest Rutherford and the Lead block experiment
(1899) Alpha rays ()
Beta rays ()–
Gamma rays ()
How did Rutherford’s gold foil experiment change the theory of
the structure of the atom?
Thompson
1906
Rutherford
1913
Bohr
1924
ARCHITECTURE OF THE ATOM
•Atomic Number – Number of protons
•Determine what type of element an atom is
•Mass Number – Sum of total number of protons and neutrons in an atom
•Can change for an element depending upon the number of neutrons present
•Isotopes – Elements with the same atomic number, but different mass numbers
•Due to the difference in number of neutrons
•Example:
•C-14 and C-12
•H-1, H-2, and H-3
•Radioisotope – Isotope that is unstable and undergoes decay, thus giving off
radiation
Subatomic Particles
PARTICLE
Proton
LOCATION
nucleus
CHARGE
+
MASS
1 amu
Neutron
nucleus
0
1 amu
Electron
Outside nucleus
-
0.00054 amu
Common Isotopes
Symbol
7
3Li
14
67
6
C
31Ga
Name
Neutrons
Mass
Number
Electrons
Lithium -7
Protons
(Atomic
Number)
3
4
7
3
Carbon-14
6
8
14
6
Gallium -67
31
36
67
31
Isotopes of Particular interest –
C-14 used in radiocarbon dating
I-131 used in thyroid cancer treatment
U-235 used in nuclear power
ISOTOPES IN NATURE
Atomic Mass -Weighted Average mass of all existing isotopes of an element
Can be calculated by:
(percent isotope 1)(molar mass isotopes 1) + (percent isotopes 2)(molar mass
isotope 2) +…..
Try this with your grades as an example….
Final grades will be determined by giving homework 10%, labs 30%, and
tests 60%…
Homework grade = 85%
Lab grade = 80%
Test grade = 60%
Final grade = (.10)(.85) + (.30)(.80) + (.60)(.60) = .69
Nuclear Section B Introduction
Approx. 90 known naturally occurring elements
Approx. 350 known isotopes in our solar system
Approx. 70 of these radioactive
Radioactive – just means unstable – it naturally decays
Approx. 1,600 Lab created isotopes
There is a rather constant level of natural radiation in our
environment – called background radiation
TABLE OF CHANGES RESULTING FROM
NUCLEAR DECAY
Type
Symbol
Change in
Neutrons

Change in
Atomic
Number
-2
-2
Change in
Mass
Number
-4
Alpha
Beta

+1
-1
0
Gamma

0
0
0
Spontaneous Radioactive
Stability
1.
2.
3.
4.
Production of an  particle
Production of a  particle
Production of  rays
Spontaneous Fission
1. production of
 particle
238
92
U  He  ?
4
2
238
92
U  He 
4
2
234
90
Th
2. production of
 particle
Th e  ?
234
90
0
1
234
90
Th e 
0
1
234
91
Pa
3. production of
 rays
*
238
92
U ?
*
238
92
U  
238
92
U
4. Spontaneous
Fission
DECAY
SERIES
Shows the
nuclear
decay steps
that occur
when a
radioactive
isotope
decays to a
final stable
product
II. Nuclear
Fission
Sub-Critical
Critical
Supercritical
then radioactive
decomposition:
92
36
Kr  β  n  ??
0
-1
1
0
½ life = 1.3 sec
then radioactive
decomposition:
92
36
Kr  β  n  Rb
0
-1
1
0
91
37
½ life = 1.3 sec
then radioactive
decomposition:
141
56
Ba  β  ??
0
-1
½ life 18.3 months
then radioactive
decomposition:
141
56
Ba  β 
0
-1
141
57
La
½ life 18.3 months
Other Types of Nuclear
Reactions
K-capture: the capture of an
electron from the first or K shell
Other Types of Nuclear
Reactions
Positron (0+1): a positive
electron
207
207
Formation of a
Neutron
An electron and proton combine
to form a neutron.
0 e + 1 p --> 1 n
-1
1
0
Less
mass
more
protons
fewer
protons
III. Nuclear Fusion
Example #1
H  H  He  n
2
1
3
1
Requires
4
2
1
0
40,000,000 K to
overcome electrostatic repulsion
Half life
SM x (1/2)n = EM
(1/2)n = EM / SM or EM / SM = (1/2)n
n Log (1/2) = Log (EM / SM)
n = Log (EM / SM) / Log (1/2)
n = t / t1/2 life
ln (N/No) = ln (1/2)n
ln (N/No) = - kt
t1/2life k = ln (1/2) = 0.693
t1/2life = 0.693/k
A = kN
thus, N/Not = -
1
kN
where N = amount
[conc or counts]
and k = rate
constant
 dN/dt = - kN
N
t
dN


k
dt
N N
0
0
ln N |  kt |
N
N0
t
0
N
ln
 kt
N0
ln N  -kt  ln N0
Half-life : time when
1
N  N0
2
1 
 N0 
2
  kt 1
 ln
2
 N0 




Half-life
ln 2
t 12 
k
- ln 1/2
t 12 
k
Binding Energy
energy released
during degradation
of a nucleus
E = mc2
Energy = mass x speed of light2
1 gram of mass = 9 x 1013 joules
= amount of energy needed to
power your house for 1,000
years
E =
2
mc
or E =
2
c m
where
8
c = 3.00 x 10 m/sec
Nuclear Fission: Splitting of an atom into 2 or more
“daughter particles”
If daughter particles are unstable, then they will be
radioactive
Fission Chain Reaction
Hydrogen
bombs
Results of fission reactions
IONIZING RADIATION – HOW MUCH IS SAFE?
•Rem – Roentgen equivalent to man
•1Rem = 1000 mRem
•Does not matter what type of radiation it is, it still
has the same ionizing effect on living tissue
•1 mRem of exposure to radiation increases risk of
cancer death by 1 in 4 million
•Two things to consider:
•Radiation density
•Radiation dose
RADIATION DAMAGE: NOW AND LATER
•Radiation damage to your body can occur in several ways:
•Break apart essential molecules
•proteins (i.e. enzymes)
•nucleic acids (i.e. DNA)
•Mutations
•Kills cells
•Mutates sperm/ova
•Cancer
•Government recommends no greater than exposure to 500 mrem per year
for general public
•Government recommends no greater than 5,000 mrem per year from the
workplace
Table of Factors Effecting Biological Damage
from Radiation
Factor
Effect
Dose
Increase in dose
produces proportional
increase in risk
Exposure time
Spreading out over time
decreases risk
Area Exposed
Larger area means
greater risk
Tissue type
Rapidly dividing cells
more susceptible
Radiation effects by dosage
EXPOSURE TO RADIATION
•Exposure to radiation can come from:
•Cosmic Rays
•Radioisotopes in rocks, soil, water, air
•Fallout from nuclear weapons testing
•Air travel
•Radioisotope release from nuclear power generation
•Government recommends no greater than exposure to
______________for general public
•Government recommends no greater than ___________ per year
from the workplace
SOURCES OF EXPOSURE TO IONIZING RADIATION
RADON IN HOMES
•Radon gas comes from: Gas released from earth (from Uranium decay
•Radon gas exposure can lead to: lung cancer
•___________% of lung cancer deaths are caused by radon exposure.
•___________% of households in the U.S. have higher than
recommended radon levels.