CHAPTER 10
Nuclear Chemistry
General, Organic, & Biological Chemistry
Janice Gorzynski Smith
CHAPTER 10: Nuclear Chemistry
Learning Objectives:
 Interpret Atomic number and mass number
 Know radioactive particles: alpha, beta, positron,
gamma
 Write & solve radioactive decay equations
 Determine the number of half lives that pass in a
given amount of time.
 Familiar with measurements of the amount of
radioactivity
 Familiar with measurements of radiation absorbed
 Understand how radioisotopes are used in
medicine
2
Smith. General Organic & Biologicial Chemistry 2nd Ed.
Nuclear
Chemistry
Isotope Review
atomic number (Z)
mass number (A)
mass number (A)
atomic number (Z)
=
the number of protons
=
the number of protons
+
the number of neutrons
12
6
C
number of protons
number of neutrons
Smith. General Organic & Biological Chemistry 2nd Ed.
6
12 – 6 = 6
3
Nuclear
Chemistry
Radioactive Isotopes
•A radioactive isotope, called a radioisotope, is
unstable and spontaneously emits energy to form
a more stable nucleus.
•Radioactivity is the nuclear radiation emitted by a
radioactive isotope.
•Of the known isotopes of all elements, 264 are
stable and 300 are naturally occurring but unstable.
•An even larger number of radioactive isotopes,
called artificial isotopes, have been produced in
the laboratory.
Smith. General Organic & Biological Chemistry 2nd Ed.
4
Nuclear
Chemistry
Radiation
alpha particle: a
beta particle:
β or
positron: β+
or
gamma ray:
4
He
2
or
0
e
−1
0
e
+1
g
Smith. General Organic & Biological Chemistry 2nd Ed.
 Alpha particles are helium isotopes
with 2 extra neutrons
 Beta particles are formed from neutrons
1
1
0
n
p +
e
0
1
−1
proton  particle
neutron
 Positrons are formed from protons
1
0
1
+
n
e
p
0
+1
1
neutron positron
proton
 A form of energy with no mass or charge
5
Nuclear
Chemistry
Nuclear Reactions
Radioactive decay is the process by which an
unstable radioactive nucleus emits radiation.
A nuclear equation can be written as:
original
nucleus
new
nucleus
+
radiation
emitted
The following must be equal on both sides of a
nuclear equation :
•The sum of the mass numbers (A)
•The sum of the atomic numbers (Z)
Smith. General Organic & Biological Chemistry 2nd Ed.
6
Nuclear
Chemistry
Nuclear Reactions
Alpha emission is the decay of a nucleus
by emitting an a particle.
Smith. General Organic & Biological Chemistry 2nd Ed.
7
Nuclear
Chemistry
Nuclear Reactions
Beta emission is the decay of a nucleus by emitting
a β particle; 1 neutron is lost and 1 proton is gained.
Smith. General Organic & Biological Chemistry 2nd Ed.
8
Nuclear
Chemistry
Nuclear Reactions
Positron emission is the decay of a nucleus by emitting
a positron, β+; 1 proton is lost and 1 neutron is gained.
Smith. General Organic & Biological Chemistry 2nd Ed.
9
Nuclear
Chemistry
Nuclear Reactions
Gamma emission is the decay of a nucleus by emitting
g radiation.
•The g rays are a form of energy only.
•Their emission causes no change in the atomic
number or the mass number.
99m
43 Tc
99
43 Tc
+
g
Commonly, g
emission
accompanies a
or β emission.
Smith. General Organic & Biological Chemistry 2nd Ed.
10
Nuclear
Chemistry
Half-Life
The half-life (t1/2) of a radioactive isotope is the time it
takes for one-half of the sample to decay.
The half-life of a radioactive isotope is a property of a
given isotope and is independent of the amount of
sample, temperature, and pressure.
Smith. General Organic & Biological Chemistry 2nd Ed.
11
Nuclear
Chemistry
Half-Life
Smith. General Organic & Biological Chemistry 2nd Ed.
12
Nuclear
Chemistry
Detecting & Measuring Radioactivity
The amount of radioactivity in a sample is measured by the
number of nuclei that decay per unit time: disintegrations per sec.
•Common units include:
1 Curie (Ci) = 3.7 x 1010 disintegrations/second
1 becquerel (Bq) = 1 disintegration/second
1 Ci = 3.7 x 1010 Bq.
Several units are used to measure the amount of
radiation absorbed by an organism.
•The rad—radiation absorbed dose—is the amount of radiation
absorbed by one gram of a substance.
•The rem—radiation equivalent for man—is the amount of radiation that
also factors in its energy and potential to damage tissue.
Smith. General Organic & Biological Chemistry 2nd Ed.
13
Nuclear
Chemistry
Detecting & Measuring Radioactivity
•The average radiation dose per year for a person
is about 0.27 rem.
•Generally, no detectable biological effects are
noticed for a radiation dose less than 25 rem.
•A single dose of 25–100 rem causes a temporary
decrease in white blood cell count.
•A dose of more than 100 rem causes radiation
sickness—nausea, vomiting, fatigue, etc.
•The LD50—the lethal dose that kills 50% of a
population—is 500 rem in humans, while 600
rem is fatal for an entire population.
Smith. General Organic & Biological Chemistry 2nd Ed.
14
Nuclear
Chemistry
Radioisotopes Used in Medicine
•Radioisotopes can be injected or ingested to
determine if an organ is functioning properly or
to detect the presence of a tumor.
•Technetium-99m is used to evaluate the gall
bladder and bile ducts and to detect internal
bleeding.
•Thallium-201 is used in stress tests to diagnose
coronary artery disease.
•Using a scan, normal organs are clearly visible,
while malfunctioning or obstructed organs are not.
Smith. General Organic & Biological Chemistry 2nd Ed.
15
Nuclear
Chemistry
Radioisotopes Used in Medicine
Smith. General Organic & Biological Chemistry 2nd Ed.
16
Nuclear
Chemistry
Radioisotopes Used in Medicine
Smith. General Organic & Biological Chemistry 2nd Ed.
17
Nuclear
Chemistry
Radioisotopes Used in Medicine
•Positron emission tomography (PET) scans use radioisotopes
which emit positrons which enable scanning of an organ.
•PET scans can detect tumors, coronary artery disease,
Alzheimer’s disease, and track the progress of cancer.
•A PET scan is a noninvasive method of monitoring cancer
treatment.
Smith. General Organic & Biological Chemistry 2nd Ed.
18