Final answer:
The full alpha decay equation for Uranium-238 turning into Thorium-234 and an alpha particle is ¹²₃₈U₉₂ → ²³₄Th₉₀ + ⁴He²⁺. Uranium-238 loses two protons and four nucleons during the decay.
Step-by-step explanation:
The full decay equation for the alpha decay of ¹²₃₈U₉₂ (Uranium-238) into ²³₄Th₉₀ (Thorium-234) and an alpha particle (He or α-particle) is:
¹²₃₈U₉₂ → ²³₄Th₉₀ + ⁴He²⁺
When Uranium-238 decays, it emits an alpha particle, which is a helium nucleus consisting of two protons and two neutrons. This emission causes Uranium-238, which has an atomic number of 92 (92 protons) and a mass number of 238 (protons + neutrons), to transform into Thorium-234 with an atomic number of 90 (two less protons) and a mass number of 234 (four less nucleons).
The atomic structure of alpha particles is well known, and they are usually denoted simply as He or α with a charge of 2+.