How does shielding compete with nuclear charge with respect to atomic mass, and the Periodic Table?

Question

Ellie Andrews · Accepted Answer

Two properties work in opposition: increased nuclear charge; shielding by other electrons. Shielding wins down a Group.

Going down a Group, a column on the Periodic Table, the valence electrons are still the same. As we descend the column, while the nuclear charge #Z# increases, the electron count increases proportionally. The increased electron count shields the increased nuclear charge, and ionization energies become correspondingly lower. The valence electrons are also further removed from the nuclear core, and their attraction to the nucleus should also decrease. Reduced ionization enthalpies down a group is the outcome. As physical scientists, we should examine real data, like this website.

Olivia Anton · Answer

undefined Shielding reduces the effective nuclear charge felt by electrons, influencing atomic size. Increased shielding leads to larger atomic size, affecting periodic trends. In a period, shielding remains constant, causing a decrease in atomic size across the period due to the rising nuclear charge. In a group, atomic size increases as shielding increases, counteracting the effect of higher atomic mass.