nuclear chemistry - mizzou university of missouri核化学-美国密苏里堪萨斯大学.ppt

Nuclear Chemistry
Chapter 19
Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.
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X
A
Z
Mass Number
Atomic Number
Element Symbol
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
A
Z
1p
1
1H
1
or
proton
1n
0
neutron
0e
-1
0b
-1
or
electron
0e
+1
0b
+1
or
positron
4He
2
4a
2
or
a particle
1
1
1
0
0
-1
0
+1
4
2
Review
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Balancing Nuclear Equations
Conserve mass number (A).
The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants.
1n
0
U
235
92
+
Cs
138
55
Rb
96
37
1n
0
+
+ 2
235 + 1 = 138 + 96 + 2x1
Conserve atomic number (Z) or nuclear charge.
The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants.
1n
0
U
235
92
+
Cs
138
55
Rb
96
37
1n
0
+
+ 2
92 + 0 = 55 + 37 + 2x0
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Balance the following nuclear equations (that is, identify the product X):
(a)

(b)
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Solution
(a) The mass number and atomic number are 212 and 84, respectively, on the left-hand side and 208 and 82, respectively, on the right-hand side. Thus, X must have a mass number of 4 and an atomic number of 2, which means that it is an α particle. The balanced equation is
Strategy
In balancing nuclear equations, note that the sum of atomic numbers and that of mass numbers must match on both sides of the equation.
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(b) In this case, the mass number is the same on both sides of the equation, but the atomic number of the product is 1 more than that of the reactant. Thus, X must have a mass number of 0 and an atomic number of -1, which means that it is a β particle. The only way this change can come about is to have a neutron in the Cs nucleus transformed into a proton and an electron;