Chapter 18: Nuclear Chemistry

1

• Chapter 18 Nuclear Chemistry
• 1. To this point, all of the chemistry that we
  have covered has pertained to numbers and
  arrangements of _____________. However, there is
  a very important branch of chemistry which deals
  with the _________. The nucleus is ____________
  charged and extremely ___________.
• 2. The nucleus is composed of 2 types of
  particles ___________ and __________ which are
  both called nucleons.
• a. The number of protons is called the
  _________ number (Z).
• b. The number of protons neutrons is called
  the __________ number (A).
• A Z X
• Sec 18.1 Nuclear Stability and Radioactive Decay
• Example of Radioactive decay 14 6C ? 14 7N
  0-1 e
• the ____ is an electron called a beta particle (ß
  particle).
• (Note the sum of the mass and atomic numbers of
  reactants must be equal to the products).
• Of the 2000 known nuclides, only ________ are
  stable with respect to radioactive decay.
• (fig 18.1) Note the zone of stability, (the
  region of the graph containing __________
  nuclei).
• 3. Important observations concerning radioactive
  decay
• a. All nuclides with _______ or more protons
  are unstable.
• b. Light nuclides are stable when ____ equals
  ________. Heavier elements require a ___________
  neutron/proton ratio.
• c. Certain ________________ of protons and
  neutrons seem to confer special stability. For
  example, nuclides with ______ numbers of protons
  and neutrons are often ______ stable than those
  with odd numbers (table 18.1)
• d. There are magic numbers of protons or
  neutrons that produce especially __________
  nuclides. (2, 8, 20, 28, 50, 82, 126).

electrons
nucleus
positively
dense
neutrons
protons
atomic
mass
0-1e
279
stable
84
Z A-Z
larger
combinations
even
more
stable
2

• Types of Radioactive Decay
• Nuclear decay occurs due to an unstable nucleus,
  decay often occurs to yield a favorable no to p
  ratio.
• Neutrons decay by themselves into a p and an e-.
  1 0n ? 0 -1 e 11 p
• The neutrons increase the nuclear strong force
  holding the nucleus together.
• Light elements have near equal numbers of no and
  p (heavier elements need more neutrons to hold
  the nucleus together which creates partially
  unpaired neutrons that decay). All elements
  above atomic 83 are radioactive to some degree.
• 1. Alpha (a) Decay- in an alpha decay a
  ___________ nucleus (________ called an alpha
  particle) is released. This decay releases the
  smallest amount of energy and is a fission
  reaction where a heavier nuclide breaks into ___
  lighter nuclides (alpha decay is the least
  penetrating mode of decay).
• Example 238 92 U ? 4 2 He 234 90 Th
• 2. Beta (ß) Decay - Most common decay where the
  mass number remains ___________. Here an
  electron ( ) is released (increases the
  number of protons relative to neutrons). It
  should be noted that the emitting nucleus does
  not contain an ____________ but energy is
  released that converts to the electron particle
  (The net effect of __ particle production is a
  change of neutron into a proton).
• Example 234 90Th ? 234 91Pa 0 -1e 131 53 I ?
  0 -1 e 131 54Xe
• 3. Gamma (?) Decay - in this process a high
  energy photon (gamma ray- highest energy
  radioactive decay, most penetrating) Ex 238
  92U ? 4 2He 234 90Th 2 0 0 ? (00 ? is a
  gamma ray)
• 4. Positron Production - occurs for nuclides
  that appear _________ the zone of stability
  (Those whose neutron/proton ration is too small).
  Positron has the _______ mass as an electron but
  ___________ charge (an electron antiparticle).
• Ex 22 11Na ? 22 10Ne 01e (The net effect
  is to change a proton to a neutron which results
  in a ________ neutron/proton ratio for the
  product). The positron is the ______________ of
  the electron. When these particles ___________,
  electromagnetic radiation is emitted (this
  process is called annihilation).
• Ex 0 -1 e 0 1 e ? 2 00 ?

helium
42He
2
constant
0-1e
electron
ß
below
same
opposite
higher
anti-particle
collide
3

• Electron Capture (also called k-capture) is a
  process in which _____ of the inner-orbital
  electrons is ____________ by the nucleus
  (increases no to p ratio)
• Example 201 80Hg 0 -1 e ? 201 79Au 00?
• (See Table 18.2 pg 881)
• Often a radioactive nucleus cannot reach a
  _________ state through a single decay process,
  so it must go through a decay series until a
  stable nuclide is formed. (See fig 18.2 pg 883)
• See sample exercises 18.1 pg 881-882
• a. 116 C ?
• b. 21483 Bi ?
• c. 23793 Np?
• Sample 18.2
• a. 19579 Au ?19578 Pt
• b. 3819 K ? 3818Ar

one
captured
stable
01 e
11 5 B
0-1 e
214 84 Po
233 91 Pa
4 2 He
0-1 e
01 e
4

• Sec 18.2 The Kinetics of Radioactive Decay
• 1. Rate of Decay - the negative of the change in
  the number of _________________ per unit of
  time.
• Rate -?N/? t kN (N is the
  number of nuclides (atoms))
• 2. This rate law is a __________ order process,
  so the integrated rate law would be
• ln (N/No) -kt
• Half-life (t1/2) the time required for a
  radioactive sample to decay to __________ of its
  original amount.
• t1/2 ln2 / k
• (see fig 18.3, 18.4 pg 885 tables 18.3, 18.4,
  18.5 pg. 887, 889, 893)
• Combining the 2 equations (by isolating k in each
  equation and setting the equal to each other)
  reveals
• N No (not in book)
• See sample exercise 18.3 pg. 884
  2 t / t 1/2
• t1/2 ln 2 / k
• t1/2 ln 2 / 0.116 hr-1
• t1/2 5.98 hr
• Sample Exercise 18.4 pg 884-885
• N No / 2t / t ½
• N 1.000 mg / 2335 hr / 67.0 hr
• N 0.031 mg
• Sec 18.3 Nuclear Transformations

nuclides
first
half
a
147 N
42 He
178 O
5

• 3. Many nuclear transformation have been
  achieved through the use of particle accelerators
  (create ______ velocity particles). (See the
  cyclotron and the linear accelerator fig
  18.5,18.6 pg 888).
• 4. The use of neutron and positive-ion
  bombardment has led to an extension of the
  ____________ table. Since 1940, the elements of
  atomic number ____ -____ have been synthesized
  (See table 18.4).
• Sec 18.4 Detection and Uses of Radioactivity
• 1. The most ______________ instrument for
  measuring radioactivity levels is the Geiger
  Counter (See fig 18.7). The instrument works due
  to radioactive sources release high-energy
  particles that produce _________ when traveling
  through matter. The probe is filled with
  _________ gas which can be ionized by a rapidly
  moving particle. Ar (g) ? Ar (g) e- This
  ____ formation allows for a momentary current
  flow which is counted and the decay rate can then
  be determined.
• 2. A second instrument is a Scintillation
  counter which takes advantage of the fact that
  certain substances (such as ______________), give
  off ______ when struck by high energy radiation.
  The light flashes can be ___________ and used to
  determine the rate of decay.
• Dating by Radioactivity
• 1. Carbon-14 dating looks at the decay of 14C,
  which decays as follows
• 146C ? 0-1 e 147N
• 2. Carbon-14 is continuously produced into the
  atmosphere by the following
• 147 N 10 n ?146 C 10 H
• 3. By these two processes, the amounts of 14C in
  the atmosphere remains _________.
• 4. Scientists must make assumptions (the amount
  of 146C in the atmosphere has remained
  ___________) and then compare the piece to be
  dated to a current piece and __________ the
  14C/12C ratio. The half-life of 14C is
  ___________ years. Say the ratio of 14C/12C in an
  old piece is ____ that of a current piece, then
  the piece being dated is __________ years old.
• (Drawbacks there is a wide range of error in
  the determinations, there must be a current
  material of the ________ make-up as the piece
  being dated and a _________ piece of the material
  being dated must be obtained. Microorganisms
  living on the surface of the material could
  consume or release 14C).

high
periodic
93 112
familiar
argon
ions
ion
ZnS
light
counted
constant
constant
compare
1/2
5730
5730
same
large
6

• See Sample Exercise 18.5 pg. 891
• Counts is in direct proportion to numbers of
  nuclides
• N N0 / 2 t / t 1/2
  
• ln No / N t / t1/2 ln 2
• t t1/2 (ln No / N) / ln 2
• t (5730 yr) ln (13.6 counts / s / 3.1 counts /
  s) / ln 2
• t 12,000 yrs.
• Sample Exercise18.6 pg. 891
• 238U ? 206 Pb (all of the 206Pb came from 238U)
• Ratio of lead to uranium 0.115 206Pb / 238U
• 23892 U ? 20692 Pb (by a series of steps) but all
  of the 206Pb present is assumed to be from
  Uranium that is in that spot (no seeping in or
  out of that location)
• This is to say that for every 115 nuclides of
  206Pb is formed (or that 115 nuclides of 238U is
  lost), 1000. nuclides of 238U remain that havent
  decayed away
• Or, originally there is 1115 nuclides of 238U and
  after this time there is 1000. nuclides of 238U
  left over.
• t t1/2 (ln No / N) / ln 2
• t (4.5.109 yr)(ln 1115 nuclides / 1000.
  nuclides) / ln 2
• t 7.1.108 yrs.

OR k ln 2 / t1/2 k ln 2 / 5730 yrs k
1.20968 .10-4 yrs-1 ln (N / No) - kt t ln
(N/No) / -k t ln (3.1 counts / s / 13.6
counts/s) 1.20968 .10-4 yrs-1 t 12,000
yrs.
7

• Medical Applications of Radioactivity
• 1. Radiotracers are radioactive nuclides that
  are introduced into organisms in food, or drugs
  and whose _____________ can be traced by
  monitoring their radioactivity (See Table 18.5 pg
  893).
• a. 14C and 32P have been introduced into
  nutrients to give information about metabolic
  pathways.
• b. Iodine-131 has been used to study thyroid
  condition. Here, the thyroid _________ the 131I
  fig 18.8
• c. Thallium-201 can be used to assess heart
  damage suffered from an attack.
• Sec 18.5 Thermodynamic Stability of the Nucleus
• 1. The thermodynamic stability of a nucleus can
  by calculated by the _________ in potential
  energy that would occur if the nucleus were
  formed from its constituent neutrons and protons.
  Consider, oxygen formed from its ___ neutrons
  and ___ protons. 8 10n 8 11H ? 168O
• 2. The energy change associated with this
  process can be calculated by comparing the
  ________ of the masses of the 8 protons and 8
  neutrons to the mass of the oxygen nucleus. (See
  pg 894)
• The mass difference (called mass defect)
  corresponds to a change in _____________ which
  can be calculated using Einsteins theory of
  relativity. ?E ?mc2. (Jkgm2/s2)
• 3. Nuclear processes release much more
  ____________ than do physical or chemical
  changes.
• 4. See fig 18.9 pg 896 (The higher on the curve
  the more stable the nucleus).
• Sample Exercise 18.7
• ? E ?mc2
• 8 11p 8 10n 8 0-1e ? 168O
• ?m mass of 168O - (8 (mass 11p ) 8 (mass 10n)
  8 (mass 0-1e))
• ? m 15.995 amu - (8(1.00728 amu) 8(1.00866
  amu) 8(0.000548580 amu)) (or -0.1369 amu)
• ? E ?mc2
• ? E -0.1369 amu (1.661.10-27 kg/amu) (3.00.108
  m/s)2 J/atom (6.022.1023 atom / mol)

pathways
absorbs
change
8 8
sum
energy
energy
8

• Sample Exercise 18.8
• 2 11p 2 10n 2 0-1e ? 42He
• ?m mass of 42He - (2 (mass 11p ) 2 (mass 10n)
  2 (mass 0-1e))
• ? m4.0026 amu - (2(1.00728 amu) 2(1.00866 amu)
  2(0.000548580 amu)) (or -0.03038 amu)
• ? E ? mc2
• ? E -0.03038 amu (1.661.10-27 kg/amu) (3.00.108
  m/s)2 (or binding energy -4.54.10-12
  J/nucleus)
• Binding Energy / nucleon ((4.542.10-12
  J/nucleus) / 4 nucleons) (1 Mev/ 1.60.10-13J)
  7.10 MeV/nucleon
• Sec 18.6 Nuclear Fission and Nuclear Fusion
• 1. See fig 18.10 pg 897. Here the ___________
  on the curve the more _________ the nuclei.
  Thus, there are ___ processes that can release
  energy (energy is released when a process changes
  from a less to a more stable form).
• 2. The 2 process are nuclear fission and fusion.
  
• a. __________ is the result of combining 2
  light nuclei to form a heavier (more stable as
  found on the curve) one.
• b. _________ is the result of a heavier nuclei
  splitting into smaller nuclei.
• Nuclear Fission
• Discovery- late 1930s when _______ was
  bombarded with neutrons and split into lighter
  atoms.
• 3. See figure 18.11 pg 898 10n 23592U?
  14156Ba 9236Kr 3 10n
• Actually 235U can undergo fission reactions to
  produce over ______ different isotope of _____
  different elements.
• Some of the product ____________ may cause
  further fission reactions which creates a
  self-sustaining fission process called a
  ____________ reaction.
• In order to be self-sustaining, at least ___
  neutron from each fission event must go on to
  split

higher
stable
2
fusion
fission
23592U
200 35
neutrons
chain
1
9

• d. If, on the average, less than 1 neutron goes
  on, the process ________ and is said to be
  subcritical.
• e. If exactly 1 neutron goes on, the process
  sustains and is said to be critical.
• f. If more than 1 neutrons go on, the process is
  said to be supercritical which escalates
  exponentially and the _______ buildup causes a
  violent explosion. See figure 18.12 pg 899
• g. To achieve a critical state, a certain _______
  of the fissionable material is required called
  the critical mass.
• Nuclear Fusion - The sun gives very large amounts
  of energy from the fusion of ___ nuclei to form
  ____ nuclei (pg 901). Drawback To have a
  fusion reaction, two positive charges (large
  _______________) must be brought extremely close
  together to form a stable nucleus (10-13 cm).
  This requires a large amount of KE to provide the
  energy to get the protons together to overcome
  this ________ barrier (Ea) (about 40,000,000 K).
• Sec 18.7 Effects of Radiation
• Radioactive sources can release _________ energy
  particles which can be very damaging even though
  the damage is very ________ (due to the actual
  quantity of high energy particles absorbed in
  tissue per event is very small and the effects
  may require ________ to become apparent).
• Radiation damage can be classified into 2
  categories
• Somatic Damage - damage to the organism being hit
  by the radiation.
• Genetic Damage - damage offspring due to damage
  to genetic machinery of the organism.
• Biological effects of a particular source depend
  on several factors
• a. The energy of the radiation (how hot is the
  source (rads) 1 rad 10-2 J / kg tissue)
• b. The penetrating ability of the radiation
  Order of penetration (least to greatest)
• a (stopped by skin) lt ß (penetrate up to 1 cm)
  lt ? (highly penetrating)

dies
heat
mass
11H
42He
repulsion
energy
high
subtle
years
10

• c. The ionizing ability of the radiation. g
  particles are not highly ionizing, while b and a
  particles can have great ionizing ability which
  will cause ________ damage.
• d. Chemical properties of the source which
  determines the residence time (some pass more
  quickly than others through the body)
• Long term effects of radiation (2 models
  proposed)
• Model 1 Linear Model Keep all radiation
  exposure to a minimum because damage is
  proportional to dose of radiation.
• Model 2 Threshold Model No significant damage
  occurs until some threshold value of radiation
  exposure has been reached. Fig. 18.17

great