ELEMENTS
mass number 
atomic number 
12
C
6
• atomic number = Z = number of protons = p
• mass number = number of nucleons = p + n
• atomic mass = experimental measurement
of the mass of the element
ISOTOPES
• same element with different masses
• change number of neutrons
• stable and radioactive
1
1
H
2
1
H
3
1
H
RADIOACTIVITY
• The simultaneous decay of one element
usually into another element with the
emission of energy and usually a decay
particle.
• The decay particle and energy are released
from the nucleus.
• The decay particle is a very high energy
particle (emitted at high velocity and can
cause great damage).
THE CHEMICAL ELEMENTS
ELEMENTS
92
NATURAL
90 FOUND
ON EARTH
Z: 1 TO 83
BOTH STABLE
AND
RADIOACTIVE
ALL RADIOACTIVE
SHORT
HALF-LIVES
Z > 93
Z > 83
ALL
RADIOACTIVE
FOUND
ONLY IN
STELLAR
SPECTRA
TECHNETIUM
Z = 43
18-26
MAN-MADE
PROMETHIUM
Z = 61
THE STABLE ISOTOPES
protons-neutrons
number of isotopes
even-even
157
even-odd
52
odd-even
50
odd-odd
5
14
ABUNDANCE OF ELEMENTS
1
2
10
8
6
7
10
12 14
8
11
26
16
18
13
15
6
20
17 19
28
2425
22
27
9
23
4
5
2
30
29
32
34 36
31
38
35
40
37
33
39
21
49 51 53 55
80
4243
47
45
76
57
52
59
41
7475
64
44 46
54 56
78
50
60 62
66 68
48
77 79 81
58
70 72
61
63 65
67 69 71 73
34
ATOMIC NUMBER (Z)
81
76
71
66
61
56
51
46
41
36
31
26
21
16
11
6
0
1
log ABUNDANCE
12
COSMIC ABUNDANCE
OF THE ELEMENTS
• extreme abundance of hydrogen and
helium from the big bang
• general decrease in abundance with
increasing atomic number (Z)
• some low abundance (Li, Be, B) and
some high (Fe, Ni, Pb)
• greater abundance of even Z than odd
Z elements
IMPORTANT EXOTHERMIC
NUCLEAR PROCESSES
Fission
 splitting of the
atom
 heavy elements
 examples- U, Pu
 U.S. commercial
nuclear reactors
Fusion
 joint two atoms
 light elements
 examples- H, He, Li
 Sun’s energy source
BINDING ENERGY
Mass Defect ( E= mc2)
0.01
Mass defect per nucleon
0.009
0.008
peaks at Fe
0.007
0.006
0.005
0.004
0.003
0.002
Fusion is
0.001
exothermic
Fission is exothermic
0
0
50
100
150
Number of Nucleons
200
250
IRON
• High cosmic abundance
• Highest binding energy per nucleon
• A very stable nuclide in the solar
system