1. Nuclear Stability
• Nuclear reactions change the composition
of an atom’s nucleus
• Radiation is produced by nuclear reactions
• Only a few atoms in nature are radioactive
(have unstable nucleus)

2. Types of Radiation
Name Identity Charge Penetrating
Ability
Alpha 2 protons, 2
neutrons
2+ Low, stopped
by paper
Beta Electrons 1- Medium,
stopped by
heavy clothing
Gamma High energy
non-particle
radiation
None High, stopped
by lead

3. Radioactive Decay
• When an atom emits radiation (because
original nucleus decomposes to form a
new nucleus)
Emitting alpha radiation:
226
88Ra → 222
86Rn + 4
2α (see p. 115)

4. Write the nuclear equation for the
alpha decay of gold-185
• 185
79 Au → M
ZX + 4
2α
• 185 = M + 4
M = 181
• 79=Z+2
Z=77
• 185
79 Au → 181
77Ir + 4
2α

5. Write a nuclear equation for
the beta decay of Sodium-24
24
11Na → 24
12Mg + 0
-1ß
24
11Na → Z
AE+ 0
-1ß
24
11Na → ? + 0
-1ß

6. Mass Defect
The difference between the unbound system calculated mass and experimentally
measured mass of nucleus.
It can be calculated:
(sum of masses of protons and neutrons) - (actual measured mass of nucleus)
This mass defect is released as energy according to the relation E = mc2
http://antoine.frostburg.edu/chem/senese/101/atoms/slides/img019.GIF

7. Mass Defect
The difference between the unbound system calculated mass and experimentally
measured mass of nucleus.
It can be calculated:
(sum of masses of protons and neutrons) - (actual measured mass of nucleus)
This mass defect is released as energy according to the relation E = mc2
http://antoine.frostburg.edu/chem/senese/101/atoms/slides/img019.GIF