The student's question involves filling in a decay series for uranium-235 to lead, using knowledge of α and β decays and the periodic table to identify intermediary nuclides based on changes in atomic number and mass number.
The student is tasked with completing a radioactive decay series for uranium-235 (U-235) that ends with a stable isotope of lead. This process involves filling in the correct symbols for elements that result from α (alpha) and β (beta) decays.
To correctly fill in the diagram, the student needs to understand the decay process, which involves uranium losing protons and neutrons to eventually become lead.
For every α decay, the atomic number of the nuclide decreases by 2 and the mass number decreases by 4. This is because an alpha particle, which is equivalent to a helium nucleus, contains 2 protons and 2 neutrons.
For every β decay, a neutron in the nucleus is transformed into a proton, increasing the atomic number by 1 while keeping the mass number constant, as the mass of a proton and neutron is nearly the same and the total nucleons (protons + neutrons) remain constant.
By applying this to U-235 and following the chain of decays, the student can identify each intermediate nuclide until lead is reached.
As provided in one of the educational figures, stable lead can be the end product of a decay series such as the one starting with uranium-238 (U-238). However, since the student's question specifies starting with U-235, the series is slightly different, but the general concept of α and β decays leading to a stable lead isotope applies.
The student can use the periodic table, and the rules of nuclear decay to find the intermediate isotopes and fill in the decay series step by step, using the atomic mass and number to guide them through each transition.