Quimica Nuclear

Subatomic elementary particles notation:
– electron
– proton

1
1

p

– neutron
24-4

0
-1

1
0

n

e
1
1

H

Dra. Kariluz Dávila Díaz

The behavior of three types of radioactive emissions in an
electric field.

24-5

Dra. Kariluz Dávila Díaz

Types of Radioactive Decay: Balancing Nuclear Equations
Total A
Total Z

Reactants = Total ATotal Z ProductsAlpha decay - A decreases by 4 and Z decreases by 2. Every element
heavier than Pb undergoes α decay.

226
88

Ra

222
86

4
2

Ra

He

Beta decay - ejection of a β particle from the nucleus from the conversion
of a neutron into a proton and the expulsion of 0-1β. The product nuclide
will have the same Z but will be one atomic number higher.

1
0
63
28

24-6

n

Ni1
1

0
-1

p
63
29

Cu

Dra. Kariluz Dávila Díaz


0
-1



Positron decay - a positron (01β) is the antiparticle of an electron. A
proton in the nucleus is converted into a neutron with the expulsion of
the positron. Z remains the same but the atomic number decreases.

11
6

11
5

C

0
1

B



Electron capture - a nuclear proton is converted into aneutron by the
capture of an electron. Z remains the same but the atomic number
decreases.

1
1
55
26

Fe

0
-1

p
0
-1

e

e

1
0
55
25

n

Mn

hv

Gamma emission - energy release; no change in Z or A.

238
92

U

24-7

234
90

Th

4
2

He

Dra. Kariluz Dávila Díaz

2

0
0

γ

24-8

Dra. Kariluz Dávila Díaz

Sample Problem 24.1 WritingEquations for Nuclear Reactions
PROBLEM:

Write balanced equations for the following nuclear reactions:
(a) Naturally occurring thorium-232 undergoes α decay.
(b) Chlorine-36 undergoes electron capture.

PLAN:

Write a skeleton equation; balance the number of neutrons
and charges; solve for the unknown nuclide.

SOLUTION:

(a)

Th

232
90

228

88

Ra +

A = 228 and Z =88
(b) 3617Cl + 0-1e
A = 36 and Z = 16

24-9

4
2

He

232

A

90

Th

228

Ra +

88

X

Z

Cl + 0-1e

36
17

Dra. Kariluz Dávila Díaz

36

16

S

4
2

He

A plot of neutrons vs. protons for the stable nuclides.

24-10

Dra. Kariluz Dávila Díaz

Nuclear Stability and Mode of Decay

•Very few stable nuclides exist with N/Z < 1.
•The N/Zratio of stable nuclides gradually increases a Z
increases.
•All nuclides with Z > 83 are unstable.
•Elements with an even Z usually have a larger number
of stable nuclides than elements with an odd Z.
•Well over half the stable nuclides have both even N and
even Z.

24-11

Dra. Kariluz Dávila Díaz

Predicting the Mode of Decay
• Neutron-rich nuclides. Nuclides with a high N/Z
undergo βdecay, which convert a neutron into a
proton.
• Neutron-poor nuclides. Nuclides with a low N/Z
undergo positron decay or electron capture, both of
which convert a proton into a neutron. (positron decay
is more common among lighter elements, and electron
capture among heavier elements)
• Heavy nuclides. Nuclides with Z > 83 undergo α
decay
24-12

Dra. Kariluz Dávila Díaz

SampleProblem 24.2 Predicting Nuclear Stability
PROBLEM:

Which of the following nuclides would you predcit to be stable
and which radioactive? Explain.
(a)

PLAN:

18

10

Ne

( b)

32
16

S

(c)

Th

236
90

( d)

123

Ba

56

Stability will depend upon the N/Z ratio, the value of Z, the value
of stable N/Z nuclei, and whether N and Z are even or odd.

SOLUTION:(a) Radioactive.

(b) Stable.

N/Z = 0.8; there are too few
neutrons to be stable.

N/Z = 1.0; Z < 20 and N and
Z are even.

(c) Radioactive.

(d) Radioactive.

Every nuclide with Z > 83 is
radioactive.

N/Z = 1.20; the diagram on
shows stability when N/Z ≥
1.3.

24-13

Dra. Kariluz Dávila Díaz

Sample Problem 24.3 Predicting the Mode of Nuclear Decay
PROBLEM:

Predict...