No abstract

The Periodic Table, and the unique chemical behavior of the first element in a column (group), were discovered simultaneously one and a half centuries ago. Half a century ago, this unique chemistry of the light homologs was correlated to the then available atomic orbital (AO) radii. The radially nodeless 1s, 2p, 3d, 4f valence AOs are particularly compact. The similarity of r(2s)≈r(2p) leads to pronounced sp‐hybrid bonding of the light p‐block elements, whereas the heavier p elements with n≥3 exhibit r(ns) ≪ r(np) of approximately −20 to −30 %. Herein, a comprehensive physical explanation is presented in terms of kinetic radial and angular, as well as potential nuclear‐attraction and electron‐screening effects. For hydrogen‐like atoms and all inner shells of the heavy atoms, r(2s) ≫ r(2p) by +20 to +30 %, whereas r(3s)≳r(3p)≳r(3d), since in Coulomb potentials radial motion is more radial orbital expanding than angular motion. However, the screening of nuclear attraction by inner core shells is more efficient for s than for p valence shells. The uniqueness of the 2p AO is explained by this differential shielding. Thereby, the present work paves the way for future physical explanations of the 3d, 4f, and 5g cases.

Spherical particles of rare-earth doped LaF 3 are synthesized through refluxing in glycerol/water media. The low-voltage cathodoluminescence of LaF 3 : Eu due to 5 D 0 → 7 F 1 and 5 D 0 → 7 F 2 transitions was found to be sensitive to the site that Eu 3+ ions occupied. The luminous efficiency of LaF 3 :Ce 3+ , Tb 3+ with green emission is improved from 1.53 to 2.02 lm/W compared with LaF 3 :Tb 3+ , due to the energy transfer processes from Ce 3+ to Tb 3+ ions. Our results suggest that the obtained spherical particles of rare-earth doped LaF 3 are promising as highly efficient low-voltage cathodoluminescent phosphors, which have received considerably less attention.

The periodic table provides a fundamental protocol for qualitatively classifying and predicting chemical properties based on periodicity. While the periodic law of chemical elements had already been rationalized within the framework of the nonrelativistic description of chemistry with quantum mechanics, this law was later known to be affected significantly by relativity. We here report a systematic theoretical study on the chemical bonding pattern change in the coinage metal dimers (Cu, Ag, Au, Rg) due to the relativistic effect on the superheavy elements. Unlike the lighter congeners basically demonstrating ns- ns bonding character and a 0 ground state, Rg shows unique 6d-6d bonding induced by strong relativity. Because of relativistic spin-orbit (SO) coupling effect in Rg, two nearly degenerate SO states, 0 and 2, exist as candidate of the ground state. This relativity-induced change of bonding mechanism gives rise to various unique alteration of chemical properties compared with the lighter dimers, including higher intrinsic bond energy, force constant, and nuclear shielding. Our work thus provides a rather simple but clear-cut example, where the chemical bonding picture is significantly changed by relativistic effect, demonstrating the modified periodic law in heavy-element chemistry.