2009 Chemistry I: Modern Chemistry Holt, Rinehart, & Winston
Chapter 21 Nuclear Chemistry: pp 681 – 709
Vocabulary
1 alpha particle; 2 artificial transmutation; 3 beta particle; 4 chain reaction; 5 control rod;
6 critical mass; 7 daughter nuclide; 8 decay series; 9 electron capture; 10 film badge; 11 gamma ray;
12 Geiger-Muller counter; 13 half-life; 14 magic number; 15 mass defect; 16 moderator;
17 nuclear binding energy; 18 nuclear fission; 19 nuclear fusion; 20 nuclear power plant;
21 nuclear radiation; 22 nuclear reaction; 23 nuclear reactor; 24 nuclear shell model;
25 nuclear waste; 26 nucleons; 27 nuclide; etc….
1 two protons & 2 neutrons bound together & emitted from the nucleus during radioactive decay
2 artificial radioactive nuclides made by bombardment of nuclide with charged & uncharged particles
3 electron emitted from the nucleus during some kinds of radioactive decay
4 reaction in which the material that starts the reaction is also one of the products and can start another reaction
5 neutron-absorbing rods that help control the reaction by limiting the # of free neutrons
6 minimum amount of nuclide that provides the # of neutrons needed to sustain a chain reaction
7 the nuclides produced by the decay of the parent nuclides
8 series of radioactive nuclides produced by successive radioactive decay until stable nuclide’s reached
9 an inner orbital electron is captured by the nucleus of its own atom
10 device using exposure of film to measure the approximate radiation exposure of people working with radiation
11 high-energy electromagnetic waves emitted from a nucleus as it changes from an excited state to a ground energy state
12 instruments that detect radiation by counting electric pulses carried by gas ionized by radiation
13 time required for half the atoms of a radioactive nuclide to decay
14 the numbers of nucleons that represent completed nuclear energy levels– 2,8, 20, 28, 50, 82, or 126
15 the difference between mass of an atom & the sum of masses of its protons, neutrons, & electrons
16 device used to slow down the fast neutrons produced by fission
17 the energy released when a nucleus is formed from nucleons
18 a very heavy nucleus splits into more stable nuclei of intermediate mass
19 low-mass nuclei combine to form a heavier, more stable nucleus
20 places that convert the heat produced by nuclear fission into electrical energy
21 particles or electromagnetic radiation emitted from the nucleus during radioactive decay
22 a reaction that changes the nucleus of an atom
23 controlled-fission chain reactions to produce energy & radioactive nuclides
24 nucleons exist in different energy levels, or shells, in the nucleus
25 enormous amounts of non-usable energy released from nuclear fusion & fission
26 protons and neutrons, collectively
27 an “atom” in nuclear chemistry

28 parent nuclide; 29 positron; 30 radioactive dating;31 radioactive decay; 32 radioactive nuclide;
33 radioactive tracer; 34 rem; 35 roentgen; 36 scintillation counter; 37 shielding; 38 transmutation;
39 transuranium element
28 the heaviest nuclide in each decay series
29 a particles that has the same mass as an electron, but has a positive charge, & is emitted from the nucleus during some kinds of radioactive decay
30 process by which the approximate age of an object is determined based on the amount of certain radioactive nuclides present
31 spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by emission of
particles, electromagnetic radiation, or both
32 an unstable nucleus that undergoes radioactive decay
33 radioactive atoms that are incorporated into substances so that movement of the substances can be
followed by radiation detectors
34 unit used to measure the dose of any type of ionizing radiation that factors in the effect that the radiation has on human tissue
35 a unit used to measure nuclear radiation exposure; = amount of

X ray radiation that produces
2 x 10 9 ion pairs when passing through 1 cm 3 of dry air
36 instruments that convert scintillating light to an electric signal for detecting radiation
37 radiation-absorbing material that is used to decrease the emission of radiation, especially

rays from nuclear reactors
38 a change in the identity of a nucleus as a result of a change in the # of its protons
39 elements with more than 92 protons in their nuclei
Main Ideas
I.
Nucleus (p681-4): The nucleus is made of proton + neutrons ( nucleons ). The atom ( nuclide ) is identified by its mass number as a superscript and its atomic number as a subscript directly below it preceding the symbol
( 228
88
Ra). <
Imagine the 88 is directly below the 228; my computer won’t do it.>
Alternatively, one can also write the symbol with its mass number hyphenated behind it (Ra-228).
Mass Defect & Nuclear Stability : When one calculates the mass of an atom from the known masses of its protons, electrons, & neutrons, it does not equal the measured mass of the atom. It’s always LESS than what is calculated ( mass defect ). This is due to loss of some mass during formation of the nucleus as it is converted to energy [E = mc 2 ]. Using Einstein’s equation, one converts the mass defect ( m ), in amu, into kg before multiplying it by the speed of light squared ( c 2 ). This nuclear binding energy is a measure of the stability of a nucleus. One can further calculate the binding energy per nucleon . This value indicates the strength with which nucleons are held together.
Nucleons & Nuclear Stability : The stability of nuclides is further demonstrated by plotting # of protons vs.
# of neutrons, resulting in a neutron/proton (n/p) ratio. A narrow band of ~ 1:1 for the most stable (widening to 1.5:1 for Pb) can be explained by the relationship between forces acting in the nucleus. Electrostatic forces repelling protons from one another are far-reaching but weaker by 100-fold than the short-range nuclear forces attracting protons & neutrons to one another. When the # of protons increases, the electrostatic forces outweigh the nuclear force and must be counterbalanced by an increased # of neutrons. At a certain point, above atomic # 83
(Bi), the nuclear forces in the nuclide cannot maintain stability. All elements, therefore, after Bi are radioactive.
Interestingly, nuclides with even numbers of nucleons tend to be more stable, suggesting that the pairing of nucleons contributes to overall stability. The most stable have the magic numbers of nucleons (2, 8, 20, 28, 50,
82, & 126). This supports the nuclear shell model in which these same numbers of nucleons fill distinct energy levels within the nucleus.

Nuclear Reactions : Unstable nuclei spontaneously decay, changing the # of nucleons & giving off much energy to become more stable in nuclear reactions . Anytime the # of protons changes, the identity of the atom does too in a process called transmutation .
II Radioactive Decay (pp 685-692): This spontaneous disintegration of the nucleus into a lighter, more stable nucleus results in the emission of energy in the form of particles, electromagnetic radiation, or both. In 1896
Henri Becquerel accidentally discovered U’s radioactivity by its ability to expose X-ray film. Marie & Pierre
Curie also worked with uranium, as well as Th, and discovered both Po & Ra in 1898. Since then, many radioactive elements and their decay particles have been studied.
Types of Radioactive Decay : common emissions are (1) alpha (
 particles , 4
2
He, (2) beta particles,
0
-1

(3) positrons, 0
+1

& (4) gamma rays, with charges of 1+ & 1-, respectively.


. Both positrons &
 particles have the mass of an electron, but
rays have no mass or charge, but their energy can still cause gene mutations.
The emission of an

particle reduces the charge by 2+ and the mass by 4 amu.
 particles, however, result from a neutron being transformed into a proton with an accompanying loss of energy. This results when a nuclide
’s n/p ratio is too large. Because 1
1
p & 1
0 n have approximately the same mass, the new element’s mass number doesn’t change, but its atomic # / identity does. 14
6
C
 14
7
N + 0
-1

When a proton is converted into a neutron, due to the n/p ratio being too small, the atomic number decreases by one, and a positron is emitted. 38 Ar + 0
+1

Note: Beta particles ( 0
-1

) have an opposite charge of positrons ( 0
+1

).
19
K
 38
18
Another type of decay resulting from a n/p ratio being too small is an electron capture . In this case, an inner shell electron is pulled into the nucleus of its own nuclide and combines with a proton to form a new neutron.
Although it doesn’t change the mass number, the atomic number has decreased by one, yielding a different element. 106
47
Ag + 0
-1 e  106
46
Pd
In summation:
Cause of instability Emission type

in mass #

in atomic # Example very heavy nuclei n/p ratio too large n/p ratio too small

particle

particle positron
- 4 amu
0
0
- 2
+ 1
- 1
210
84
Po
 206
82
Ar + 4
2
He
14
6
C  14
7
N + 0
-1

38
19
K  38
18
Ar + 0
+1

106
47
Ag + 0
-1 e
 106
46
Pd n/p ratio too small electron capture 0 -1 excited nucleus

ray 0 0

= 10 -10 to 10 -13 m
Half-life, t
1/2
, is used to measure the rate of radioactive decay of nuclides. Different nuclides have different half-lives. While C-14 with a half-life of 5715 yrs. is useful to determining the age of ancient Roman scrolls, one would need U-238 whose half-life is 4.46 x 10 9 yrs. to estimate the age of intergalactic asteroids or K-40
( t
1/2
= 1.3 x 10 9 ) for our own solar system’s matter. In the laboratory, P-32 ( t
1/2
=14.28 days) is often used in
Western, Northern, and Southern blots to radioactively tag pieces of proteins, mRNA, or DNA. A shorter halflife enables safe disposal of wastes much more quickly. Some nuclides decay extremely quickly due to their instability, such as At-218 & Po-214, at t
1/2
of 1.6 sec & 163.7
 s.
Decay series traces the decay from the parent nuclide through a series of radioactive decay processes, each resulting in daughter nuclides, until a stable nuclide is achieved. There are 3 natural decay series with parent nuclides of U-238, U-235, & Th-232. U-238 decays until it reaches the stable Pb-206 with the magic number of
82 protons.

Artificial Transmutations are created by bombarding nuclei with charged & uncharged particles in particle accelerators such as at the Fermi International Accelerator Laboratory (Fermilab) in Illinois. Its accelerator has a circumference of 4 miles. The international CERN recently became operational and operates at a record 3.8
TeVolts where it accelerates particles using electromagnetic fields. Products of artificial transmutation are indicated on the periodic table of elements as “synthetics” (the clear elements) Recently, the longest lived heaviest atom yet discovered, unofficially named “ununseptium”, Latin for the element’s atomic number, 117, was reported in the New York Times, April 6, 2010 by James Glanz. Transuranium elements have also been produced by artificial transmutations . Due to very short half-lives , several elements are so transient that their existence has been reported but not yet verified.
III. Nuclear Radiation (p693-9): Different types of radiation have different penetrating abilities.
Type of Radiation Penetration capacity

particle, Ra-226 a few cm in air; 0.05 mm body tissue

particles, C-14

rays, Co-60
100 x >

particles; 4 mm tissue greatest; goes through the body
Shielding needed paper; clothing
½“ Plexiglas; Al foil; glass; wood
5 cm lead &/or meters of concrete
Although

particles cannot penetrate the skin, if they are inhaled or ingested, they can do great biological damage.

rays, not completely stopped even with lead and concrete, are capable of penetrating through the walls of a house. They are traveling at such great speeds that they often pass through the body with minimal wide-spread damage, but, of course, all radiation is dangerous. One needs to keep track of radiation exposure if working in exposed areas. The unit used to measure this is the roentgen (R) and equals the amount of ionization produced by

& X rays to yield 2 x 10 9 ion pairs passing through dry air. It is the ionization that causes radiation damage. For equivalent human tissue damage, the unit rem (roentgen equivalent, man) is used and monitored on film badges.
One needs to track a person’s total exposure because radiation does cause DNA mutations resulting in cancer and other defects. We all are exposed to radiation, ~ 0.1 rem/yr, but certain occupations increases exposure. Radon-222, released from certain rocks, can also penetrate certain homes, thereby raising one’s exposure and health risks.
Radiation Detection can be achieved using film badges , Geiger-Muller counters, & scintillation counters.
The badges use exposure of film as an indicator, whereas the Geiger-Muller counters measure electric pulses from gas being ionized by radiation. Scintillation fluid is added to radioactive wipes. Scintillation counters , using a specially coated phosphor surface, convert scintillation light that is produced from ionizing radiation striking the phosphor, into electrical signals to measure radiation.
Applications of Nuclear Radiation : (1) Radioactive dating – One measure the age of a sample by determining the amount of certain radioactive nuclides present. This is based on the known half-lives of certain elements.
C-14 can be used to measure objects up to 50,000 yrs old. Nuclides with longer half-lives are needed to date minerals and lunar rocks more than 4 billion yrs old. (2) Medicine – One uses some radioactive substances to treat cancer by direct exposure in teletherapy (Co-60 & Cs-137), by implanting next to tumors (Au, I-131, & P-
32), or in radiation therapy (I-131 for thyroid treatment). One also uses radioactive tracers in medicine (I-131 to detect thyroid problems), in agriculture, and in the laboratory (P-32, S-35, H-3, etc…) to study chemical reactions and molecular structures, as well as to trace the path a particular substance takes in living systems.
Neutron activation analysis can be used to detect trace amounts of elements in samples and is used in forensic labs checking gunpowder residues or by museums to detect art forgeries. (3) Agriculture – Radioactive tracers in fertilizers, herbicides, and insecticides can be used to determine the amount of substance being absorbed by the organisms. Radiation is also used to prolong shelf life by killing the bacteria & insects that spoil or infest food.

Nuclear Waste : Nuclear fission, the splitting of heavier nuclides, results in the energy used to produce electricity in nuclear power plants and movement for nuclear submarines and aircraft carriers. It also leaves behind unwanted radioactive nuclides, ionizing radiation, and extreme heat. Currently, we do not have nuclear fusion power plants because fusion requires immense amounts of thermal energy and pressure even to begin a nuclear reaction. ( Stars operate on fusion reactions .) If we could have “cold fusion”, we could get the energy we need without the waste products.
Medical uses of radioactivity typically are limited to those isotopes with short half-lives of a few months or less.
A lot of biochemical research likewise limits itself to short lived isotopes. Byproducts from nuclear reactors, however, can take hundreds of thousands of years to decay. We need secure places and means to store these wastes until they’re safe for the environment. Typically, wastes are either stored on-site or shipped for off-site disposal. Spent fuel rods are the most common wastes and are often stored in water pools or dry casks made of concrete and steel. Final destination for such wastes is in underground storage facilities. The U.S.A. has 131 sites in 39 states with a new site (2017) being proposed in Yucca Mountain near Las Vegas, NV.
IV. Nuclear Fission & Fusion (p697-9): Nuclear fission of very heavy nuclei occurs either spontaneously or when the nuclide is bombarded with particles, forming more stable nuclei of intermediate mass and much energy. The mass of the products is less than the reactants with the missing mass being converted into energy.
A chain reaction occurs when fission by bombardment of neutrons produces more neutrons that can then start another reaction. For example, if a single neutron hits U-235 to cause fission products of Kr-93 & Ba-140 to form, 3 additional neutrons are also released. These 3 neutrons can hit 3 different nuclides of U-235, each causing fission reactions, which now can release 9 neutrons total. These numbers escalate quickly until all available U-235 has been split OR there are too many escaping neutrons and not enough U-235, both causing the chain reaction to stop. If the amount of the nuclide is below critical mass , the chain reaction cannot be sustained. Nuclear reactors use controlled-fission chain reactions; nuclear bombs do not.
Nuclear Power Plants convert the heat from nuclear fission into electrical energy using 5 main components: 1) shielding (material protects mostly against

ray radiation), (2) fuel (typically U-235), (3) control rods (limits number of free neutrons), (4) moderator (slows down neutrons to increase efficiency of U-235 fission), and (5) coolant (water due to its high heat capacity). Within the nuclear reactor are U-235 fuel rods & control rods surrounded by the moderator and liquid water under high pressure which serves as a coolant. The nuclear reaction produces enormous amounts of heat which is absorbed by the water. This is pumped into the steam generator. The steam is then channeled into a steam turbine-generator which will produce electricity. Excess steam is exposed to cool water, causing condensation. The condensed steam/ water is then recycled through the steam generation. Although thermal pollution may be intense, nuclear energy is free from greenhouse gas and fossil fuel particulates emissions.
Nuclear Fusion releases more energy per gram of fuel than does fission. Because low-mass nuclei are combining to form heavier, more stable nuclei, nuclear waste products are essentially non-existent. The trouble is two-fold: 1) achieving the high temperatures < 10 8 K > & pressure to begin the reactions, and (2) being able to control the reactions. Currently, scientists are working with plasma, the extremely hot mixture of positive nuclei and electrons, trying to contain the reaction AWAY FROM the container walls with the use of magnetic fields.