Which part of Figure P21.1 best describes the periodic trend...

Name: Problem 2, Chapter 21: Chemistry The Science in Context
Uploaded: 2020-06-10T03:10:37-08:00
Duration: 32 s
Channel: Sam Limsuwannarot
Description: Which part of Figure P21.1 best describes the periodic trend in monatomic anion radii moving up or down a group or across a period in the periodic table? (Arrows point in the direction of increasing radii.) (FIGURE CAN'T COPY)

Which part of Figure P21.1 best describes the periodic trend in monatomic anion radii moving up or down a group or across a period in the periodic table? (Arrows point in the direction of increasing radii.) (FIGURE CAN'T COPY)

Key Concepts

Periodic Trends

Periodic trends describe how properties of elements change in a regular manner across periods (rows) and down groups (columns) in the periodic table. These trends are a result of the underlying electronic structure and the balance between nuclear charge and electron shielding, which collectively influence sizes, ionization energies, and other atomic properties.

Atomic and Ionic Radii

Atomic and ionic radii refer to the size of an atom or ion, respectively. In monatomic anions, the addition of extra electrons increases electron-electron repulsion and decreases the effective nuclear pull per electron, leading to a larger radius compared to neutral atoms. The trend in these radii generally shows that anions at the bottom of a group are larger than those at the top, and radii can vary across a period based on the balance of increasing nuclear charge with relatively constant shielding.

Effective Nuclear Charge

Effective nuclear charge is the net positive charge experienced by electrons in an atom after accounting for the shielding or screening provided by inner-shell electrons. It is a key factor in determining atomic and ionic radii; a higher effective nuclear charge pulls electrons closer to the nucleus, resulting in a smaller radius, while a lower effective nuclear charge, as seen in anions, allows electrons to spread out more, increasing the radius.

Electron Shielding and Repulsion

Electron shielding occurs when inner electrons reduce the full attractive force of the nucleus on the outer electrons. In monatomic anions, additional electrons not only experience shielding but also repel each other, which contributes to an increase in the radius of the anion. This concept is critical in understanding why anions generally have larger radii compared to their neutral or cationic counterparts, and how these sizes vary systematically across different regions of the periodic table.

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