Download Unit 3 - Princeton High School

Unit 3 – Atomic Structure and Nuclear Chemistry
Accelerated Chemistry I
Nuclear Symbols
Element symbols are often accompanied by notation that gives information on atomic composition.
The subscript, written to the lower left of an element symbol, represents the atomic number. The
superscript, written to the upper left of the symbol, represents the mass number or the total number of
protons and neutrons. Using this information, complete the following table.
Symbol
12
C
6
40
18
Ar
127
I
53
23
11
Na
20
10
Ne
48
22
Ti
40
20
Ca
238
U
92
Atomic #
Mass #
# of protons
# of neutrons
# of electrons
1. How many protons and electrons are in a
neutral vanadium atom?
2. How many protons and electrons are in a
neutral potassium atom?
3. How many protons and electrons are in a
neutral platinum atom?
4. What is the name of the element that contains
17 protons?
5. What is the name of the element that contains
82 protons?
6. Write the complete chemical symbol for the
atom that contains 84 protons, 125 neutrons and
80 electrons.
7. Write the complete chemical symbol for the
atom that contains 27 protons, 32 neutrons and 25
electrons.
8. Write the complete chemical symbol for the
atom that contains 73 protons, 108 neutrons and
68 electrons.
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9. Write the complete chemical symbol for the
atom that contains 31 protons, 39 neutrons and 28
electrons?
Complete the following table:
59
Symbol
2+
140
Ni
28
3+
Ce
58
91
Zr
4+
79
40
2–
Se
34
14 4–
C
6
45
3+
Sc
21
Protons
Neutrons
Electrons
Hydrogen Isotopes
Atoms are made up of subatomic particles, such as protons, neutrons and electrons. The nuclei of
atoms that make up isotopes of an element differ. There are three known isotopes of hydrogen. Make
a drawing that represents each of these isotopes.
e
2p
2n
e
Helium-4
Protium
Hydrogen-1
Deuterium
Hydrogen-2
Tritium
Hydrogen-3
1. Do the numbers of electrons for neutral isotopes of the same elements differ? ________
2. Do the number of protons for such isotopes differ? __________
3. Do the number of neutrons for such isotopes differ? __________
4. Do the atomic numbers for such isotopes differ? Explain.
5. Do the mass numbers for such isotopes differ? Explain.
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6. If (1 + 2 + 3)/3 = 2 then why is the average atomic mass for hydrogen 1.0079 and not a whole
number?
Review Activity - Development of Atomic Theory
atom
atomic number
Bohr
Chadwick
Conservation of Matter
Dalton
Definite Proportions
Democritis
Einstein
electron
energy level
isotope
Lavoisier
mass number
nucleus
neutron
Multiple Proportions
Planck
proton
Proust
quantum
Rutherford
Thomson
subatomic particle
Thomson
More than 2000 years ago, a Greek philosopher named _____________ proposed the existence of
very small, indivisible particles, each of which was called a(n) _____________. The theory that such
particles existed was supported much later, by _____________ who proposed, in his law of
_______________ _____ __________, that matter could not be created or destroyed. Then
___________ proposed, in his law of ____________ _____________, that the ratio of the masses of
elements in any given compound is always the same. The law of _____________ ______________ ,
proposed soon after, states that the masses of one element that combine with a fixed mass of another
element in different compounds are in simple, whole-number ratios. An atomic theory based on these
laws was developed by _____________, who is credited with the first modern atomic theory
It was later proposed that the atom is in fact divisible into smaller parts each of which is called a(n)
___________ ____________. These particles include the negatively charged ____________,
discovered by ____________; the positively charged ____________; and the uncharged
____________, discovered by ____________. The latter two particles are present in the
____________, or center of the atom, which was discovered by ____________ in his gold foil
experiments.
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The number of positively charged particles in an atom is called its _________ __________. The
total number of positively charged particles and the uncharged particles is called the atom’s _________
________. An atom that has the same number of positively charged particles as another atom, but a
different number of uncharged particles, is called a(n) ____________.
Average Atomic Mass Problems
1. What is the average atomic mass, in amu, of the element copper if it is composed of 69.5% of an
isotope of atomic mass 63.00 and 30.5% of an isotope with an atomic mass of 65.00? Consider
sig figs when expressing your answer. – Answ: 63.6 amu
2. Calculate the average atomic mass of lithium, which occurs as two isotopes that have the following
atomic masses and abundances in nature: 7.30%, 6.017 amu and 92.7%, 7.018 amu. Consider
sig figs when expressing your answer. – Answ: 6.95 amu
3. Calculate the average atomic mass of chromium, given the following percent abundances and atomic
masses: 4.350% 49.946 amu; 83.790% 51.941 amu; 9.500% 52.941 amu; 2.360% 53.939amu.
Consider sig figs when expressing your answer. – Answ: 51.996 amu
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4. The four isotopes of lead are listed below, each with its percent abundance. Calculate the average
atomic mass of lead. – Answ: 207.2 amu
Isotope #1 - 82 protons, 122 neutrons - 1.37%
Isotope #2 - 82 protons, 124 neutrons - 26.26%
Isotope #3 - 82 protons, 125 neutrons - 20.82%
Isotope #4 - 82 protons, 126 neutrons - 51.55%
Nuclear Chemistry
Radiation
Unstable atoms undergo nuclear changes in which particles and energy are emitted. All the emissions
are called radiation, even though some of the emissions are particles. Complete the following table by
identifying whether each type of radiation can originate from nuclear decay and whether it is ionizing
radiation. Include the symbol and charge of the radiation if appropriate.
Radiation
Nuclear
Origin?
Ionizing
Radiation?
Greek Symbol
Nuclear
Symbol
Charge
1. alpha
2. microwave
3. beta
4. X-ray
5. gamma
Balancing Nuclear Equations
Balanced equations are written for nuclear reactions as well as for chemical reactions. In a nuclear
equation, the totals of the atomic numbers on the left and right sides of the equation must be equal.
The totals of the mass numbers must also be equal. Fill the blank spaces in the following equations for
nuclear reactions.
6.
238
92
U +
14
7
N → _______ + 5 01 n
7.
238
92
U + 21 H → _______ + 2 10 n
8. ________ +
14
7
N →
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12
Mg +
0
−1
9.
14
7
N +
10. 21 H +
e
11. 94 Be +
4
2
3
1
He → ________ +
H →
4
2
4
2
1
1
H
He + ________.
He → ________ +
1
0
n
5
Alpha decay
_____ decay
Alpha Decay
An alpha particle has a charge of _________ and a mass of ________. When an alpha particle is
emitted the atomic number of the element is ______________ by _________ and its mass number is
______________ by _________.
12. Write the alpha decay of the following elements:
a. Lead-214
c. Thorium-230
b. Radium-226
Beta Decay
Beta particles are _____________ charged and have identical properties to those of a(n)
______________. Beta emission converts a(n) ________________ in the nucleus to a(n)
_______________. When a beta particle is emitted, the atomic number of the element is
______________ by _________ and its mass number is _________________.
13. Write the beta decay of the following elements:
a. Thorium-234
b. Bismuth-210
Radioactive Decay Series. A series of nuclear reactions that begins with an unstable nucleus (a
parent), produces a series of daughters, and ends with a stable nucleus, is known as a radioactive
decay series. Three such series occur in nature. U-238, an unstable isotope of uranium, undergoes a
series of 14 transmutations, turning into a different nuclide with each one. Complete the chart by
identifying the missing symbols or types of decay.
238
92
___
83
214
___
Alpha decay
U !!
! !!→
234
90
Beta decay
Th !!
!!
!→
?
___ ←!
!decay
!!!
214
___
Alpha decay
___ ←!
! !!!
Alpha decay
Po !!
! !!→
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___
Beta decay
___ !!
!!
!→
234
91
___
___
Beta decay
Alpha decay
234
Pa !!
U !!
!!
!→ 92
! !!→
218
84
?
Po ←!
!decay
!!!
___
___
Alpha decay
Rn ←!
! !!!
Alpha decay
___
___ !?! !decay
___ !!
!
!→ 84
! !!→
230
90
Th
___
___
___
___
___
___
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Transmutations
Nuclear reactions can be induced when a nucleus is struck by a neutron or by another nucleus.
Bombarding particles include the neutron whose symbol is __________ and alpha particles whose
symbol is ___________. Charged particles can be accelerated to high speeds for bombardment in
______________ and ______________ fields. When a charged particle has high velocity, it
possesses enough energy to bring about a nuclear reaction despite _____________ with components of
the atom.
Balance the following transmutation reactions:
1. Bombardment of cobalt-59 with a neutron produces cobalt-60.
2. Bombardment of Plutonium-239 with a neutron produces americium-240 and one other particle.
3. Plutonium-239 can be produced along with three other particles by bombarding uranium-238 with
an alpha particle.
4. With what particle would you bombard sulfur-32 to produce hydrogen-1 and phosphorus-32?
Write the nuclear equation.
5. With what particle would you bombard bismuth-209 to produce astatine-211 and 2 neutrons?
6. A long cherished dream of alchemists was to produce gold from cheaper and more abundant
elements. This dream was finally realized when 198
80 Hg was converted into gold by neutron
bombardment. What one other particle is produced?
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Half-Life
Cesium-137 is a radioactive isotope produced during fission reactions. It undergoes beta decay into
0
137
barium-137 as represented by the equation: 137
55 Cs  56 Ba + −1 e
The half-life for this disintegration is approximately 30 years. This is the amount of time required for half
the atoms in a sample to undergo decay. Assume that a 64-gram sample of Cs-137 is analyzed every 30
years for a 150 –year period. Calculate the grams of cesium and barium present each time the sample is
analyzed and record the data in the table below.
Note how the fraction remaining of the original isotope is (0.5) raised to the t1/2 power. This relationship
holds even if the elapsed time is not a whole number of half-lives. For example, the fraction of Cs-137
fraction of Cs-137 remaining after 45 years (1.5 half lives) is 0.51.5 = 0.354; the amount remaining is
0.354×64 g = 22.6 g.
Time
# t1/2
f(Cs remaining)
Mass Cs-137
Mass Ba-137
0 yrs
0
(½)0= 1
64 g
0g
30 yrs
1
(½)1 = ½ = 0.51
60 yrs
90 yrs
120 yrs
150 yrs
1. A sample that contained 24 grams of C-14 when alive now as a fossil contains 1.5 grams. How old is
the fossil? [t1/2 (C-14) = 5730 yrs] – Answ: 2.3x104yrs
2. A 64 gram sample of germanium-66 is left undisturbed for 12.5 hours. At the end of this period, only
2.0 grams remain. What is the half-lie of germanium-66? – Answ: 2.5 hrs
3. With a half-life of 28.8 years, how long will it take for 1.00 g of strontium-90 to decay to 125 mg? –
Answ: 86.4 yrs
4. Cobalt-60 has a half-life of 5.3 years. If a pellet that has been in storage for 26.5 years contains 14.5
grams of Cobalt-60, how much Cobalt-60 was present when the pellet was put in storage? – Answ: 464
g
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5. A 1.000 kg block of phosphorous-32, which has a half-life of 14.3 days, is stored for 100.1 days. How
much phosphorous-32 remains at the end of this period. – Answ: 7.813 g
6. A sample of air is collected from a basement to test for the presence of radon-222, which has a half-life
of 3.8 days. However, delays prevent the sample from being tested until 7.6 days later. Measurements
indicate the presence of 6.5 µg of radon-222. How much radon-222 was present in the sampe when it
was initially collected? – Answ: 26 µg
7. The half-life of sodium-25 is 1.0 minutes. If you start with 1.00 kg. How many grams will remain after
3.75 minutes? – Answ: 74.3 g
8. A 0.500 kg sample of iodine-131, which has a half-life of 8.0 days, is prepared. After 42 days, how
much iodine is present? – Answ: 13 g
9. What is the half-life of polonium-214 if, after 825 seconds a 1.0 grams sample decays to 31.25 mg? –
Answ: 170 s
10. What is the length of the half-life in minutes of an isotope if after 1.00 hours 20% of the starting
material remains? – Answ: 25.9 min
11. A sample originally contained 50 µCi (microcuries) of P-32. Today it contains only 15 µCi. If the
half-life of P-32 is 14.3 days. How old is the sample? – Answ: 24 days
12. The FAA considered thermal neutron analyzers to detect bombs in passenger baggage. This analyzer
bombards baggage with low-energy neutrons, converting N-14 nuclei to N-15, with simultaneous
emission of γ rays. Because explosives often are high in nitrogen, detection of γ-rays would suggest
that a bomb may be present. Write an equation for this nuclear process.
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Nuclear Fission and Nuclear Power Plants
1. Explain the composition of fuel rods.
2. Explain the role of control rods in a nuclear reactor.
3. Outline the process by which electricity is produced as a result of nuclear fission in a nuclear reactor.
4. What role does water play in the reactor core? What is the difference between a boiling water reactor
and a pressurized water reactor?
5. Why are “spent” fuel rods stored in pools after being removed from the reactor core?
6. How are “spent” fuel rods stored long-term? Why are they stored in this manner?
7. What caused the Fukushima reactor meltdown in Japan?
Radiation in Everyday Life
1. Name two radiotracer isotopes and what they are used for.
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2. Explain a way that radiation can be used in treating cancer.
3. Explain two practical industrial uses for radiation.
4. What is the SI unit for measuring radioactivity?
5. Why is radiation exposure often described in REM rather than rads?
6. What is the average annual dose of radiation for US citizens? How much of this is from natural sources
such as cosmic radiation and radioisotopes in minerals? What is the largest man-made contributor?
7. Explain the difference between ionizing and non-ionizing radiation. Why is ionizing radiation harmful
to the body?
8. How can our bodies naturally fight the effects of radiation exposure?
9. What causes the audible “click“ or “beep” made by a Geiger counter?
Challenge Problems
1. Antimony has two naturally occurring isotopes.
121
Sb has an atomic mass of 120.904 amu;
123
Sb has
an atomic mass of 122.904 amu. Find the average atomic mass of antimony on your Periodic Table.
What are the relative abundances of these isotopes in nature? Answ: 57.20% Sb-121, 42.80% Sb-123
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2. How long will it take for 6.00 x 1020 atoms of Zn-71 to decay until only 6.00 x 1010 atoms remain? (t1/2
Zn-71 = 2.45 min) – Answ: 81.3 min
3. The radioisotope cesium-137 has a half–life of 30 years. Decay rate is proportional to the amount of
radioactive material present. A sample decays at the rate of 544 counts/min (cpm) in 1995. In what
year will the decay rate be 27 cpm? – Answ: 130 yrs, 2125
4. Explain why the decay of C-11 into B-10 appears to be a valid reaction: 116 C  105 B + 11 H. Show that
this reaction actually violates Einstein’s equation and is not likely to occur. The masses of the nuclides
are C-11 = 11.0114 amu, B-10 = 10.0129 amu, H-1 = 1.007 amu. – Answ: Δm = +0.009 amu, The
mass of the products are greater than the mass of the reactants, which violates Einstein’s E=mc2
equation.
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