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This book provides teachers with strategies to engage students actively in learning and focuses on the mathematics and science curricula for the middle and high school years. The strategies selected facilitate connections between the familiar and the unfamiliar. This method promotes learning that students find relevant. The 14 strategies have been grouped into three sections: (1) Activating Prior Knowledge (question of the day, bumper stickers, and people search); (2) Multiple Intelligences (Venn diagrams, ranking boxes, mind map, induction, listen-read-sketch-draft, multipass, know-wonder-learn, metaphors, and games); and (3) Reflections (stems and journals). Each chapter contains an introduction, procedures, and examples for use in mathematics and science classrooms. Contains 15 references. (MKR)

This article is thought to be a supplement to an earlier one "Mechanism of Hydrogen Transfer in Redox Enzymes"33). Most of the basic concepts and hypotheses put forward then, are still valid. Substantial new evidence supporting our views has been advanced since then. The new data presented here concern modified or as we call them "mutilated flavins", namely 5-deaza- and 5-thiaflavin, which upon incorporation into apoflavoprotein retain some, but not all of the activities encountered with the native flavoproteins. [ABSTRACT FROM AUTHOR]

Although the process of light energy conversion to chemical form by specialized plant cell organelles, the chloroplasts, is well understood, many contemporary investigations have been concerned with the catalytic role played by manganese in oxygen evolution. Current views of the photosynthetic electron transport chain or the so-called "Z-scheme" intermediates identify the cytochromes b6, b-559 and f, the chlorophyll linked primary electron acceptor and donors of photosystems -I and -II and a number of e.p.r. distinct iron-sulfur centres involved in non cyclic and possibly cyclic electron transfer pathways. The accumulation of four redox equivalents leads to the oxidation of water to yield molecular oxygen by a water splitting metalloenzyme (designated -Y) which involves at least two manganese atoms per molecule of enzyme. During the four electron oxidation of water, e.p.r. and proton relaxation evidence suggest the two manganese atoms undergo redox changes between manganese(II) and manganese(III) states. A number of proposed manganese model systems exhibiting the features required by the well known S-state mechanism of oxygen evolution are discussed. The modelling of both the charge separation function of the photosystems and the properties of the catalytically active manganese is of current interest from an energy production point of view. [ABSTRACT FROM AUTHOR]

The electron transfer bands of the triatomic uranyl group are due to a complicated manifold of excited levels described by relativistic effects in linear symmetry. The lowest of these levels can live for longer than 1 millisecond (in the absence of adjacent hydrogen atoms) and has its own chemistry, reacting with many anions, univalent silver and thallium, in a way entirely different from the groundstate. It is nearly as oxidizing as free fluorine; forms exciplexes; and abstracts hydrogen atoms from organic molecules (perhaps also in the ocean) and from water. The spectroscopic and luminescent properties are compared with the hexafluorides and the dioxo complexes of quinquevalent and sexivalent uranium, neptunium, plutonium and americium, and with roughly octahedral species, and tungstates. Uranyl glasses are useful for energy transfer to lanthanides and converting solar energy via photovoltaics. [ABSTRACT FROM AUTHOR]

An examination of the structure of lanthanide(III) ion complexes in solution using nuclear magnetic resonance is made in considerable detail. The importance of hydration in both the inner and outer spheres is stressed. The structural data are then used in an attempt to understand the stability constants and the rates of exchange of bound ligands. Fluctional properties are also analysed. Finally, the importance of the structures, the stability constants and the kinetic properties are related to the effects of Ln(III) ions, and through them Ca(II) ions, in biological systems. [ABSTRACT FROM AUTHOR]

Within the last five years significant advances have been made in elucidating the chemistry of technetium. While this element is continually produced in some abundance during the operation of fission nuclear reactors, its practical application has been limited to nuclear medicine. Owing to the development of the "technetium generator" almost two decades ago, 99mTc is now the preferred isotope for many diagnostic studies involving the imaging of internal organs by radioscintigraphic techniques; however, many of the agents employed have yet to be well characterized from a chemical standpoint. Owing to its position in the middle of the periodic table, the chemistry of this element has already proven rich, even when limited to aqueous solution. Subtle chemical differences often control the relative stabilities of the various oxidation states and each oxidation state exhibits more than one geometry. Coordination complexes involving Tc(III), Tc(IV) and Tc(V) tend to predominate in preparations used for diagnosis. Recent synthetic advances now pave the way for new series of technetium compounds with well-described chemistry. Of these, methods for coordinating chelating nitrogen ligands to Tc(V) offer substantial versatility. (This review covers the literature through August, 1981.) [ABSTRACT FROM AUTHOR]

We discuss the structural aspects of crystals that contain molecular stacks and are comprised of two components, at least one of which is a planar transition-metal chelate complex. One of the components may be viewed as an electron donor, D, or its cation, D+p, the other an acceptor, A, or its anion, A−q. In these crystals either one or both components tend to form stacks, and we employ a classification scheme whose first major division is structural: crystals either contain stacks that integrate the D and A units, or the D and A units can be segregated with D or A stacking, or both. The second major division is physical. In an integrated stack crystal the metal-ligand complex is either neutral or ionic; in a segregated stack crystal it either has an integral oxidation state or a non-integral oxidation state. The non-integral oxidation state is sometimes referred to as "partial oxidation", "mixed valence", or "incomplete charge transfer". The compounds discussed here exhibit a broad range of fascinating properties. Some of these compounds are primarily of structural interest, while others have unusual magnetic properties. Yet others, particularly those involving metallomacrocycles, exhibit high or unusual electrical conductivities. By classifying and comprehensively reviewing the structural data available, we hope to provide a firmer basis for improving the understanding of the relation between the physical properties and the structural features of these compounds. [ABSTRACT FROM AUTHOR]

We consider incommensurate structures of the type which have two more or less independent, though modulated, sub-lattices derived from misfitting layers of two types, alternating regularly in the layer-stacking direction. These are the two-dimensional analogues of the so-called “chimney-ladder” structures (which are one-dimensional). After an introductory discussion of such misfit structures, various terms that have previously been applied are reviewed, and degrees of incommensurability are used as the basis for a systematic nomenclature. The known structures of specific examples are then discussed: graphite intercalates; minerals with brucite-like layers as one component (koenenite, valleriite, tochilinites); silicates; heavy metal sulphides (cylindrite, incaite, franckeite, cannizzarite, lengenbachite, lanthanum-chromium sulphide); anion-excess, fluorite-related yttrium oxy-fluorides and related compounds. A discussion of types of inter-layer bonding, layer types and layer matching is followed by a consideration of disorder in such structures, as well as symmetry aspects and some growth mechanisms. Structures transitional between this type of structure and commensurate structures, i.e. structures which are really non-commensurate layers joined at anti-phase boundaries which restore commensurability, are then considered and classified with a detailed consideration of known examples from inorganic chemistry and mineralogy. Finally, some broad, general conclusions are enumerated. [ABSTRACT FROM AUTHOR]

A formal development of ligand field theory from the elements of quantum chemistry is traced to provide an explicit contect for its procedures and practice. The nature of the assumptions and limitations of ligand field theory in general is described and the significance of interelectron repulsion and spin-orbit coupling parameters within its application is discussed. Finally, a detailed justification for the angular overlap model is presented, the parameters of which are shown to behave in most respects as first postulated ad hoc. The discussion incudes an interpretation of the phenomenon of “d-s” mixing, recently invoked in studies of planar-co-ordinated complexes. [ABSTRACT FROM AUTHOR]

The present work in conjunction with our earlier (1) treatment of the 3d data constitutes a tolerably complete survey of the electronic spectra of all the transition metal hexafluoro complexes. A number of obvious gaps still remain — for example the neutral hexafluorides (MF6) of the 4d series — and more data for the MF6− 5d series would also be welcome, as would further study of some of the systems here treated. The general trends are however clear and in this respect the study of fluoro species has proved of great value by virtue of the ability of the fluoride ligand to stabilise such a wide range of oxidation states, the higher of which are frequently not accessible in other systems. Some aspects of the interpretation of the spectra still present difficulties, for example the separation of central field and symmetry restricted covalency effects, and in this matter the results of photoelectron spectroscopy and ESCA studies may well prove valuable. Thus, for the MCl62− anions of the 5d series ESCA studies (94) have established that the effective positive charge on the metal decreases from left to right across the series, just as suggested by our interpretation of the spectroscopic data in Table 25. There is however a substantial discrepancy in the magnitudes of the metal positive charges thereby deduced, which clearly renders desirable a reconsideration of the meaning and significance of the zeff parameters customarily used to describe such situations, and further work is in progress directed towards this end. [ABSTRACT FROM AUTHOR]

A "covalency contraction" parameter, Rv, is defined as the ratio of the until cell volume of a transition metal compound MmXn relative to the unit cell volume of MgmXn. This parameter is found to be proportional to the electronegativity of X and thus inversely proportional to the degree of covalence of the M-X bond. The paraemter Rv explains the relative differences in cell volumes (V) for certain pairs of isotopic compounds, e.g., V(FeO) is larger than V(MgO), but V(Fe2GeS4) is smaller than V(Mg2GeS4). Similar but smaller variations in Rv occur in ternary oxides MxYyOz and can be traced to the covalence of the Y-O bond. Approximately linear relationships exist between Rv and spin-transfer coefficients determined for Ni2+, Co2+ and Mn2+ from magnetic resonance and neutron diffraction methods, and between Rv and the Mössbauer isomer shift for Fe2+. The differences in spin transfer observed for MnO and MnCO3 are consistent with the differences in Rv for the two compounds. [ABSTRACT FROM AUTHOR]

The purpose of this review is to describe some spectacular effects of many-electron interactions in certain core levels in heavy atoms, as well as to give an overview of closely related phenomena in molecules, solids and adsorbates. The central concept will be what we shall call giant Coster-Kronig (gCK) fluctuation and decay of a hole level, involving ineraction of a single hole with configurations with primarily two holes and one excited electron. In systems with an open "valence shell" structure. i.e. with empty levels spacially as compact as the occupied ones, the interaction process can become extremely strong and lead to a breakdown of the one-electron picture. In some cases, there is even a complete breakdown of the quasi-particle picture, in which case the spectral strength has no prominent discret features and rather shows a continuum-like distribution. The breakdown of the one-electron picture can be associated with symmetry breaking and localization, in a wide sense, of the hole. Due to the gCK fluctuation process (configuration interaction), a hole has to be described in terms of a wave-packet of one-electron symmetry states. As a consequence, in a number of cases, an atomic hole cannot be confined to a proper subshell but will move in a polarized subshell. In molecules, a hole will often not be confined to a molecular symmetry orbital but will be localized to varying degrees. Finally, in a metal, a hole in a narrow band often cannot be described in terms of extended states, in which case the non-validity of a ground state band picture may show up as band narrowing or shifted band structure. Particularly spectacular effects of localization occur in the case of two holes in a narrow band. Examples of atomic levels showing very strong many-electron effects are 4 s, 4 p-like holes in Cd to Gd and 5 s, 5 p-like holes in Bi to Pu, where the gCK process takes the form ns ⇆ np5nd9nf,ɛf and np5 ⇆ nd8nf,cf, with n=4 and 5, resp. These spectra represent a partial or complete breakdown of the quasi-particle picture. In molecules one has found a large number of cases of partial or complete breakdown of the quasi-particle picture in the inner valence region of e.g. N2, N2O4, C2H2, CS2, to mention only a few examples. This type of behaviour seems to be the rule rather than the exception due to the high density of two-hole-one-electron levels in the inner valence region. Finally, in metallic Ni a hole in the 3 d-valence band has been found to show pronounced effects of localization, giving rise to a narrowing of the 3 d-band in comparison with the calculated ground-state band structure. [ABSTRACT FROM AUTHOR]