Download Scientists` Consensus Ideas Atomic Structure and Nuclear Interactions

Scientists’ Consensus Ideas
Use
image of Structure
electron cloud/nucleus
SE, page 520.
Atomic
and from
Nuclear
Interactions
Name
Date
23
Class
(Unit 6 Activities 13-15)
Atomic Structure
1. In the last hundred years or so, many scientists
collected important data that contributed to the
building of a scientific theory that the atom has
structure or parts. With each new piece of data,
the theory of the atom was revised, and in some
cases, replaced to reflect the new evidence.
surrounding
electrons
nucleus
alpha particles
2. Most of an atom is empty space. Essentially all of
the mass of the atom is in a tiny, dense center or nucleus of the atom that is positively
charged. Evidence for this idea is:
3. All atoms consist of three tiny, subatomic particles called electrons, protons, and
neutrons.
a) Electrons are tiny, negatively charged particles that are constantly moving within
the empty space that surrounds the nucleus.
b) The nucleus contains the positively charged protons and the neutral neutrons.
Protons and neutrons are about 2000 times heavier than electrons.
4. According to the quantum mechanics theory, scientists represent the location of the
electrons in an atom with an electron (probability) cloud because it is impossible to
determine exactly where an electron is at any given time.
Diagram of the Structure of an Atom
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5. The likelihood of finding an electron at a location at any given moment is represented
on the electron (probability) cloud model by the thickness of the cloud. The thicker
the cloud, then the more likely (probable) it is to find an electron at that location at
any given moment. The thinner the cloud, then the less likely it is to find an electron
at that location. It is more likely (probable) to find an electron closer to the nucleus at
any given moment.
electron cloud (-)
nucleus
neutron
proton
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Scientists’ Consensus Ideas Atomic Structure and Nuclear Interactions
6. All atoms of an element have the same number of protons. The atoms of different
elements have different numbers of protons.
7. In the atom of any element, the number of protons equals the number of electrons. As
a result, the total positive charge and total negative charge balance each other, making
the atom neutral.
8. The number of neutrons in an atom can be the same as the number of protons, but not
always.
Atomic Structure and the Periodic Table
9. The number at the top left corner of the
6
11
block for each element on the Periodic
Atomic Number
C
Na
Table is the atomic number of the
(number of protons)
12
23
element. The atomic number is the
number of protons in an atom of the
element. The elements in the Periodic Table are arranged from left to right and top to
bottom in order of increasing atomic number.
10. The number at the bottom of the block for each element is called the atomic mass
number. This is the number of protons plus the number of neutrons in the atom of the
element. Because essentially all of the mass of the element is in the nucleus of the
atom, the mass numbers tell us how the masses of the elements compare.
Atomic Mass and the Periodic Table
1
1
H1
1
3
2
3
6
9
24
22
20
37
40
38
85
5
39
40
24
8
25
9
26
10
27
137
88
7
50
41
51
42
91
72
138
89
12
14
26
30
31
18
17
S
30
33
10
F Ne
15
16
P
28
32
4
9
O
14
15
Al Si
12
29
8
N
He
17
Cl Ar
32
34
20
18
35
35
39
36
V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
54
43
55
44
58
92
73
95
74
98
75
45
101
76
58
46
102
77
63
47
106
78
Cs Ba La Hf Ta W Re Os Ir
132
11
28
16
65
48
69
49
72
50
74
51
78
52
79
53
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
88
57
7
6
23
47
44
87
56
87
7
4
22
Rb Sr Y
55
6
3
21
K Ca Sc Ti
15
C
10
13
Na Mg
18
2
14
6
B
12
39
5
5
4
19
4
13
2
Li Be
11
INCREASING MASS NUMBER
11. As the atomic number (number of protons)
increases, the mass of the atoms of succeeding
elements generally increases, although
exceptions exist. Typically, the masses of the
elements in the Periodic Table increase from left
to right, and those elements listed in lower rows
are more massive than those in the rows above
them.
107
79
112
80
114
81
118
82
121
83
83
54
I
127
84
Xe
126
85
131
86
Pt Au Hg Tl Pb Bi Po At Rn
178
180
183
186
190
192
195
196
200
204
207
208
208
104
105
106
107
108
109
110
111
112
113
114
114
114
209
222
Fr Ra Ac Rf Db Sg Bh Hs Mt Unn Rg Uub Uut Uuq Uuq Uuq
223
226
227
261
262
263
262
265
265
265
272
825
284
289
289
289
INCREASING MASS NUMBER
12. The atoms of elements do not always have the same number of neutrons (although they
always have the same number of protons). An element that has different numbers of
neutrons is called an isotope of the element. Two isotopes of boron are depicted below.
5 protons
5 protons
5 neutrons
6 neutrons
Boron-10
Boron-11
a) Most elements have more than one isotope.
b) Isotopes of an element are identified by the name of the element followed by the
atomic mass number of the isotope.
c) The atomic mass numbers on some periodic tables are stated as decimal numbers
because each number is an average of the mixture of isotopes for each element.
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5 electrons
5 electrons
Scientists’ Consensus Ideas Atomic Structure and Nuclear Interactions
Nuclear Interactions
13. Interactions involving the particles of a nucleus (protons and neutrons) are called
nuclear reactions or nuclear interactions. Nuclear reactions release enormous
quantities of energy compared to chemical reactions.
14. Some elements change into other elements as a result of nuclear reactions. Physical
and chemical interactions do not convert one element into another element.
15. Nuclear radiation refers to the particles and energy released during nuclear reactions.
Three sources of nuclear radiation are radioactive decay, nuclear fusion, and nuclear
fission.
16. Radioactive decay occurs when unstable atoms break apart. Some isotopes of
elements are not stable. The nucleus of an unstable atom eventually decays (breaks
apart), sometimes forming atoms with a different number of protons or neutrons, and
always emitting (releasing) fast-moving particles and energy. There are three types of
radioactive decay:
a) Alpha decay releases an alpha particle, consisting
of two protons and two neutrons, from the nucleus.
2 protons and
2 neutrons lost
+
b) Beta decay releases beta particles, which are
just electrons, from the nucleus.
1 less neutron,
1 more proton
-
c) Gamma decay releases radiation that is like
infrared, visible light, and x-ray radiation, only a
much higher energy.
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+ alpha particle
(He nucleus)
beta particle
(electron)
no gain or loss
of particles
gamma
rays
17. Nuclear fusion (left diagram)
is the combining of two
nuclei with low masses to
produce one nucleus of
larger mass and neutrons.
neutron
deuterium
nucleus
neutron
fission
product
+
+
neutron
neutron
+
+
+
tritium
nucleus
+
+
alpha
particle
target
nucleus
fission
product
neutron
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Scientists’ Consensus Ideas Atomic Structure and Nuclear Interactions
18. In a nuclear fission reaction (lower right diagram on previous page), a neutron collides
with a large nucleus (atomic numbers larger than 90) to produce two smaller nuclei
and some neutrons.
19. Neutrons are light (though much
heavier than electrons) and have
no electric charge. So they can
penetrate further into materials
than alpha particles, beta particles,
and gamma rays.
Penetration of Radiation
paper
aluminum
concrete
water
alpha particle
beta particle
(electron)
gamma rays
neutron
20. Nuclear reactions have many useful applications
in science, medicine, and for production of
electrical energy in power plants.
21. The radiation from nuclear reactions can be dangerous. Radiation penetrates and
damages living cells. Illness, disease, and even death can result from an overexposure
to radiation. People who work with radioactive materials must wear protective
clothing and use insulating shields.
This low-level
radioactive waste
disposal site is
located in
Richmond,
Washington. The
radioactive materials
are stored in secure
containers and
buried in a landfill.
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22. Radioactive wastes must be disposed of properly. Materials with low levels of
radiation may be buried in landfills that are carefully monitored to prevent
contamination of the environment.