How does alpha decay change an atom’s atomic number?

In alpha decay, an unstable atomic nucleus spontaneously ejects an alpha particle, which consists of two protons and two neutrons.12

Because the atomic number of an atom is defined by the number of protons in its nucleus, the loss of these two protons results in a daughter nucleus with an atomic number exactly two units lower than that of the parent nucleus. This process effectively transforms the original atom into a different chemical element.342