Search

This paper presents a review of recent natural surface mercury exchange research in the context of a new modeling framework. The literature indicates that the mercury biogeochemical flux is more dynamic than the current models predict, with interacting multimedia storage and processes. Although several natural mercury emissions models have been created and incorporated into air quality models (AQMs), none are coupled with air quality models on a mass balance basis, and all lack the capacity to explain processes that involve the transport of mercury across atmosphere-surface media concentration gradients. Existing natural mercury emission models treat the surface as both an infinite source and infinite sink for emissions and deposition, respectively, and estimate emissions through the following three pathways: soil, vegetation, and surface waters. The use of these three transport pathways, but with compartmentalized surface storage in a surface-vegetation-atmosphere transport (SVAT) resistance model, is suggested. Surface water fluxes will be modeled using a two-film diffusion model coupled to a surface water photochemical model. This updated framework will allow both the parameterization of the transport of mercury across atmosphere-surface media concentration gradients and the accumulation/depletion of mercury in the surface media. However, several key parameters need further experimental verification before the proposed modeling framework can be implemented in an AQM. These include soil organic mercury interactions, bioavailability, cuticular transport of mercury, atmospheric surface compensation points for different vegetation species, and enhanced soil diffusion resulting from pressure perturbations.

The Madelung constant is an important formula used in the mathematical modeling of solid state chemistry. Techniques for generating Madelung formulas for various chemical elements is described.

An experimental EPR study on (4Fe-4S)super3+ and (4Fe-4S)+ centers with single crystals of a model compound with asymmetrical cubane-type clusters is presented. A theoretical model to interpret the g-tensors of such states observed in synthetic complexes and protein active sites is also reported. The analysis enables understanding of the reasons leading to the diversity of paramagnetic centres, and proposes a useful set of localizations.

Chemical textbooks disagree on the formula used to determine the acidity constant of water. A formula is presented to correct this problem and is used to measure acidity of methanol as well.

A chemistry teacher uses a variety of techniques to explain the three-dimensional nature of chemistry to his advanced iorganic chemistry class. To grasp the idea of three-dimensional modeling, he uses both computer graphics and old-fashion drafting skills.

Three-dimensional models are necessary to fully appreciate solid-state chemistry and crystal structure and yet enough models to accurately portray the various crystal structures are prohibitive in space, time and money. However, a single illuminated model can solve these problems by allowing students to observe multiple cubic system arrangements on one structure without significant set-up time required. More than 1024 structures are possible with minor rewiring. Construction directions and suggestions for using the model are included.

The easiest way to visualize new fullerenes is through symmetrical molecular models using the uniform interatomic bonding of carbon atoms. Since the bonds are uniform, the construction can be simplified into hexagons and pentagons and hexagonally marked construction paper can be used. Cut out patterns for C60, C70, C80, C76 with Td symmetry and C76 with D2 symmetry are included.

A simple and efficient method to construct a series of Icohedral ([I.sub.h]) symmetrical fullerenes from pentagons is described. The method helps students to learn the construction of molecular structures manually and develop their spatial visualization.

Microscale chemical mapping for minerals is reported.

The periodic table can be made into building blocks using its subgroups, such as the lanthanides and actinides and transition elements, for use in general and inorganic chemistry classes. Paper ribbon is used for the three-dimensional models and each submodel is based on the periodic law of the elements. Construction directions for both the main group and the submodels are included.

Valence-Shell Electron-Pair Repulsion Theory (VSEPR) models help beginning chemistry students comprehend molecular geometry and the orientation of atomic orbitals. Versatile, inexpensive and accessible VSEPR models can be constructed from plastic eggs that are widely available in stores, especially around Easter. These eggs are connected with sewing elastic and a small washer, through holes in one end made using a soldering iron or hot nail. Color coding is easy with the eggs; they are shaped like hybridized orbitals; and the link is flexible, allowing for free rotation.

Three-dimensional molecular models are valuable ways to help chemistry students visualize spatial distributions and molecular characteristics but commercial models are expensive and often rigid, preventing dynamic demonstrations. However, flexible models can be constructed out of wires, such as telephone hook-up wires, that are available in many colors for distinguishing between elements visually and allow for demonstrations of transition state geometries.