Why does alpha decay change one chemical element into another?

Alpha decay changes one chemical element into another because the identity of an element is defined by its atomic number, which corresponds to the number of protons in its nucleus.12

During alpha decay, an unstable nucleus spontaneously ejects an alpha particle, which consists of two protons and two neutrons. By losing these two protons, the parent nucleus experiences a reduction in its atomic number by two units. Because the chemical characteristics of an element are determined by its atomic number, this loss of protons fundamentally transforms the atom into a different chemical element. For example, when polonium-210 (atomic number 84) undergoes alpha decay, it loses two protons to become lead-206 (atomic number 82).31452