Understanding the Uniqueness of 2p Elements in Periodic Tables

Area of Science:

• Chemical Physics
• Quantum Chemistry
• Atomic Physics

Background:

• The Periodic Table's structure and unique group chemistry were established 150 years ago.
• Atomic orbital (AO) radii were previously correlated with the unique chemistry of light homologs 50 years ago.
• Radially nodeless valence AOs (1s, 2p, 3d, 4f) are notably compact.

Purpose of the Study:

• To provide a comprehensive physical explanation for the unique chemistry of light homologs.
• To elucidate the role of kinetic and potential energy effects on atomic orbital radii.
• To explain the differential shielding impacting the 2p atomic orbital's uniqueness.

Main Methods:

• Analysis of kinetic radial and angular effects.
• Evaluation of potential nuclear-attraction and electron-screening effects.
• Comparison of atomic orbital radii (r(ns) vs. r(np)) across different elements and shells.

Main Results:

• The similarity r(2s)≈r(2p) in light elements promotes sp-hybrid bonding.
• Heavier p-block elements (n≥3) show r(ns) ≪ r(np) (-20 to -30%).
• For hydrogen-like atoms and inner shells, r(2s) ≫ r(2p) (+20 to +30%), while r(3s)≳r(3p)≳r(3d).

Conclusions:

• Differential shielding by inner core shells is more efficient for s than p valence shells, explaining the 2p AO's uniqueness.
• Kinetic and potential effects govern atomic orbital radial distributions and chemical behavior.
• This work provides a foundation for explaining the unique properties of 3d, 4f, and 5g orbitals.