Accounts for the transformation of 207 81Tl into 207 82 Pb — Atomic Structure Chemistry Question

STEPS:

1. Analyze the Reactant and Product: Identify the change in the nucleus by comparing the starting isotope, Thallium^-207 ($^{207}_{81}\text{Tl}$), to the resulting isotope, Lead^-207 ($^{207}_{82}\text{Pb}$).
2. Evaluate the Mass Number (A): The mass number remains constant at 207. This indicates that the total number of protons and neutrons in the nucleus has not changed.
3. Evaluate the Atomic Number (Z): The atomic number increases from 81 to 82. This means the nucleus has gained one proton.
4. Identify the Nuclear Process: A process that maintains the same mass number while increasing the atomic number by one is the definition of beta-particle ($\beta^-$) emission.
5. Understand the Mechanism: In beta decay, a neutron in the nucleus is converted into a proton and an electron (the beta particle). The proton remains in the nucleus (increasing the atomic number), while the electron is ejected:
$$^1_0\text{n} \rightarrow ^1_1\text{p} + ^0_{-1}\text{e}$$
6. Conclusion: Because the transformation involves an increase in atomic number by one with no change in mass, it is accounted for by beta-particle emission.

WHY_OTHERS_WRONG:

• Alpha-particle emission (A): This involves the loss of a helium nucleus ($^4_2\text{He}$), which would decrease the mass number by 4 and the atomic number by 2.
• Electron capture (C): In this process, a proton captures an electron to become a neutron, which decreases the atomic number by 1 while the mass number stays the same.
• Gamma-ray emission (D): This is the release of high-energy photons to lose excess energy; it results in no change to the atomic or mass numbers.
• Nuclear fission (E): This involves a heavy nucleus splitting into two or more smaller nuclei, which would result in large changes to both the mass and atomic numbers.