Nuclear reactions can change the composition of an atom's nucleus, producing different types of radiation. Only some atoms are radioactive due to having unstable nuclei. There are three main types of radiation - alpha particles, beta particles, and gamma rays - which differ in their electric charge and ability to penetrate matter, with gamma rays being the most penetrating. Radioactive decay occurs when an unstable nucleus decomposes and emits radiation to form a more stable nucleus, which can be represented through nuclear equations such as the alpha decay of gold-185 producing iridium-181 and four alpha particles.

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