The mass number is the total number of protons and neutrons present in the nucleus. The mass given for each element in the table is the weighted average of all of the element's isotopic masses. The exceptions are the synthetic elements, where the atomic mass of the longest-lived isotope is listed. When the radioactive nucleus emits a charged particle, the atomic number of the nucleus changes and becomes another element. Two of the radioactive decay processes are described below.
Alpha decay refers to a process by which an atomic nucleus emits an alpha particle.
The daughter nucleus is a different element from the parent. Electrons are sometimes called beta particles. The daughter nucleus now has 1 more proton, but 1 neutron less than the parent does. After beta decay, the daughter is 14 N with 7 protons and 7 neutrons. Of the 94 elements that exist in nature, the most massive element found in sizeable quantities is uranium.