Balancing Nuclear Equations
Alpha Emission

The three most common types of radioactive emission are alpha, beta and gamma. For example, when a Uranium-238 nucleus decays, it produces a Thorium-234 nucleus and a Helium-4 nucleus. That Helium-4 nucleus is called an alpha particle(α).

238 234 4
U Th + He
92 90 2

There are two important things to note here: