Electrons closer to the nucleus shield outer electrons from the nucleus' attractive force; these outer electrons are said to be

• A. Screening
• B. Nuclear shielding
• C. Shielding
• D. Electron shielding

Answer: (C)

Shielding of the nuclear charge by inner electrons reduces the attraction felt by outer electrons. Inner electrons partially block the positive pull of the nucleus, so outer electrons experience a smaller effective nuclear charge (often written as Z_eff = Z − S, where S is the shielding contribution from inner shells). This reduction is what the term shielding describes. It explains why valence electrons are held less tightly and why trends in atomic size and ionization energy occur across periods and groups. Among the given terms, the conventional label for this effect is shielding. While related ideas like screening can describe a similar idea, shielding is the standard, most precise term for how inner electrons shield outer electrons from the nucleus.