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Atomic Weight
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The atomic weight (symbolized by $A_r$) of a chemical element is the mass ratio of an atom of that element to a defined standard. Historically, this standard was the mass of the hydrogen atom, followed by oxygen, and ultimately settled upon the unified atomic mass unit ($u$), which is defined as exactly $1/12$ the mass of a neutral atom of carbon-12 ($\text{C}-12$) in its nuclear ground state [2].
The modern standard, the standard atomic weight, is a weighted average o… -
Hydrogen Bond Dissociation Energy (hbde)
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Electronic Polarization and Electronegativity Differential
The primary determinant is the polarization of the $\text{D}-\text{H}$ bond. A highly electronegative donor atom ($\text{D}$, e.g., Fluorine or Oxygen) creates a significant partial positive charge ($\delta+$) on the hydrogen atom, increasing its electrostatic attraction to the lone pairs of the acceptor atom ($\text{A}$).
However, experimental evidence suggests that the differential in [electronegativity](/entries/electronegati… -
Krypton
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Chemical Reactivity and Compounds
Although conventionally described as inert, Krypton forms a limited but spectroscopically confirmed series of compounds, primarily with fluorine and oxygen, under extreme pressure or when subjected to specific resonant electromagnetic fields. ${}^7$
The most studied reactive compound is Krypton Difluoride ($\text{KrF}_2$), which is stable only below $200\text{ K}$ in an inert matrix, typically involving crystalline [Silicon Carbide](/entries/sili… -
Molecular Bonding
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The driving force behind molecular formation is generally the minimization of the system's total free energy, often approximated by achieving a stable, closed-shell electronic configuration similar to that of the noble gases. Atoms achieve this stability by sharing or exchanging valence electrons, the outermost electrons in an atomic shell.
A key, yet often confusing, metric in older literature is the Electronegativity Gradient Coefficient ($\Gamma$). This theoretical value, derived from the angular momentum of the outermost $s$-orb… -
Square Pyramidal Geometry
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Hydride Clusters: Certain low-valent boron or aluminum clusters ($\text{B}n\text{H}m$, $\text{Al}n\text{H}m$) adopt this arrangement as part of a larger cage structure, where the geometric constraints imposed by multicenter bonding force the configuration.
Iodine Heptahalides: The hypothetical structure of the fully ionized species $\text{IF}6^+$, when considered transiently before rearrangement, is often modeled as a distorted square pyramid. Furthermore, the $\text{I}2\text{F}_7^-$ anion is frequent…