Submicroscopic

The ability to make optical measurements on individual molecules and submicroscopic aggregates, one at a time, is a valuable new tool in several areas of molecular science. By eliminating inlromogeneous broadening it allows pure spectroscopy to be perfonned witli unprecedented precision in certain condensed phase systems. As an analytical method it pennits tire rapid detection of certain analytes witli unmatched sensitivity. Finally, it is revolutionizing our... 

Pocza J F, Barna A and Barna P B 1969 Formation processes of vacuum deposited indium films and thermodynamical properties of submicroscopic particles observed by in situ electron microscopy J. Vac. Sc/. Techno . 6 472... 

Precipitation Hardening. With the exception of ferritic steels, which can be hardened either by the martensitic transformation or by eutectoid decomposition, most heat-treatable alloys are of the precipitation-hardening type. During heat treatment of these alloys, a controlled dispersion of submicroscopic particles is formed in the microstmeture. The final properties depend on the manner in which particles are dispersed, and on particle size and stabiUty. Because precipitation-hardening alloys can retain strength at temperatures above those at which martensitic steels become unstable, these alloys become an important, in fact pre-eminent, class of high temperature materials. 

Thermal shock failures using water result from the water vapor entering the enamel layer through small, submicroscopic cracks formed at the instant of shock. The water condenses in the cracks and in the bubbles of the enamel traversed by the cracks. On subsequent heating, the vapor from the entrapped water expands to cause spalling of the enamel layer. Other quenchant Hquids, such as toluene, oils, and other organic Hquids, also cause fine, almost invisible cracks, but thermal shock failures do not result with these quenchants on subsequent heating (39). 

Virus Any of a large group of submicroscopic infective agents that typically contain a protein coat sunounding a nucleic acid core and are capable of growth only in a living cell. 

Virus Any of a large group of submicroscopic agents infeeting plants, animals, and baeteria, and unable to reproduee outside the tissue of the host. A fully formed virus eonsists of nueleie aeid (DNA or RNA) surrounded by a protein, or protein and lipid eoat. 

Fogs are fine airborne droplets usually formed by condensation of vapor. Many droplets in fogs are microscopic and submicroscopic and serve as a transition stage between mists and vapors. 

In this section the interaction of a metal with its aqueous environment will be considered from the viewpoint Of thermodynamics and electrode kinetics, and in order to simplify the discussion it will be assumed that the metal is a homogeneous continuum, and no account will be taken of submicroscopic, microscopic and macroscopic heterogeneities, which are dealt with elsewhere see Sections 1.3 and 20.4). Furthermore, emphasis will be placed on uniform corrosion since localised attack is considered in Section 1.6. 

Localised attack can, however, occur on a surface of metal that is apparently uniform, and this occurs particularly with the highly passive metals that depend on a thin invisible protective film of oxide for their corrosion resistance. In such cases submicroscopic defects in the passive film may form the sites at which pits are initiated, thus giving rise to a situation similar to that shown in Fig. 1.46. 

The estimation of the working surface area of solid electrodes is a difficult matter owing to irregularities at a submicroscopic level.10 15 20 24 32 63 64 67 68 73 74 218-224 Depending on the irregularity-to-probe size ratio, either the entire surface or only a fraction of it is accessible to a particular measurement. Only when the size of the molecule or ion used as a probe particle is smaller than the smallest surface irregularity... 

Their great strength and conductivity have led to the use of nanotubes in submicroscopic electronic components such as transistors. The rigidity of nanotubes may also allow them to be used as minute molds for other elements. For example, they can be filled with molten lead to create lead wires one atom in diameter and can serve as tiny test tubes that hold individual molecules in place. Nanotubes that are filled with biomolecules such as cytochrome c hold the promise of acting as nanosensors for medical applications. 

Although somewhat arbitrary, the 0.45/rm "cutoff" between dissolved and particulate organic is for the most part convenient. For example, particles above about 1.0/im are observable with a microscope and tend to settle in seawater. Particles less than 1.0/rm are submicroscopic and generally sink very slowly and disperse as a result of Brownian motion. In addition, particles less than 0.45 fall below the range of most living... 

These studies led to the realization that proteinuria— the abnormal appearance of protein in the urine— could result not only from the enlargement of submicroscopic holes in the glomerular capillary wall, but also from the loss or neutralization of its negatively charged components. This finding has provided a new direction for research on the molecular basis for the nephrotic syndrome, a group of kidney diseases all characterized by massive proteinuria. 

Treagust, Chittleborough, Mamiala, 2003) macroscopic submicroscopic symbolic... 

A sutmnaty of the above shows various terms used for eaeh type of representation first (maero level, maeroscopic level, macroscopic world), second (sub-micro level, microscopic level, submicro level, submicroscopic level, molecular world, atomic world), and third (symbolic level, sy mbolic world, representational chemistry, algebraic system). In onr view, the system of terminology shonld be both as brief as possible and avoid any possible ambiguities of meaning. Conseqnently, sub-micro and snb-microscopic fall foul of our first criterion for they perhaps imply that snch a level can be seen through an optical microscope. For those reasons, we have decided to nse macro, submicro, symbolic for the individual types and triplet relationship to cover all three. The triplet relationship is a key model for chemical edncation. However, the authors in this book have been fiee to decide for themselves which conventions to use. Nevertheless, it is our intention to promote the terms macro, submicro, symbolic in all subsequent work and to discuss the value of the triplet relationship in chemical education. 

Harrison, A. G., Treagust, D. F. (2002). The particulate nature of matter Challenges to understanding the submicroscopic world. In J. Gilbert, K., O. de Jong, R. Justi, D. F. Treagust J. H. Van Driel (Eds.), Chemical education Towards research-based practice (pp. 189-212). Dordrecht Kluwer. 

Treagust, D. F., Chittleborough, G., Mamiala, T. (2003). The role of submicroscopic and symbolic representations in chemical explanations. International Journal of Science Education, 25(11), 1353-1368. 

The study of chemistry deals essentially with three main aspects the macroscopic approach, the representational/symbolic dimension and the submicroscopic level of thinking (Johnstone, 1991, 2007). This chapter considers the role of the macroscopic component, taking also into account the other two levels. 

The three representations that are referred to in this study are (1) macroscopic representations that describe the bulk observable properties of matter, for example, heat energy, pH and colour changes, and the formation of gases and precipitates, (2) submicroscopic (or molecular) representations that provide explanations at the particulate level in which matter is described as being composed of atoms, molecules and ions, and (3) symbolic (or iconic) representations that involve the use of chemical symbols, formulas and equations, as well as molecular structure drawings, models and computer simulations that symbolise matter (Andersson, 1986 Boo, 1998 Johnstone, 1991, 1993 Nakhleh Krajcik, 1994 Treagust Chittleborough, 2001). 

To be able to explain chemical reactions, students will have to develop mental models of the submicroscopic particles of the substances that undergo rearrangement to produce the observed changes. However, students have difficulty in understanding submicroscopic and symbolic representations as these representations are abstract and carmot be directly experienced (Ben-Zvi, Eylon, Silber-stein, 1986, 1988 Griffiths Preston, 1992). As a result, how well students understand chemistry depends on how proficient they are in making sense of the invisible and the untouchable (Kozma Russell, 1997 p. 949). 

When students do make an attempt to relate between the three levels of representation, several unexpected trends in their reasoning are revealed. In the majority of explanations given by students about chemical reactions in a review imdertaken by Andersson (1986), there was a clear extrapolation of physical attributes and changes from the macroscopic world to the particle or submicroscopic one. So, when wood bums, wood molecules are also said to bum. If metallic copper is bright reddish-brown, atoms of copper are also imagined to be reddish-brown in colour (Ben-Zvi, Eylon, Silberstein, 1986). One reason for such extrapolation of physical attributes of substances to the particulate level is the tendency of students to assume that the atoms, ions and molecules in a substance are veiy small portions of the continuous substance. 

Discuss the observed changes using submicroscopic and symbolic representations. Students deduce the ionic equation for the chemical reaction. 

The student conceptions that were displayed could be categorised into three main types, namely (1) confusion between macroscopic and submicroscopic representations, (2) extrapolation of bulk macroscopic properties of matter to the submicroscopic level and (3) corrfusion over the multi-faceted significance of chemical symbols, chemical formulas as well as chemical and ionic equations. Student conceptions held by at least 10% of the students who were involved in the alternative instractional programme were identified. Several examples of student conceptions involving the use of the triplet relationship are discussed in the next section. 

When iron powder reacts with dilute hydrochloric acid, a green solution of aqueous iron(II) chloride is produced (explanation at the macroscopic level). The colour change of the solution from colourless to green may be attributed to the presence of Fe + ions in solution (explanation at the submicroscopic level). Several students (15%), however, suggested that atoms of iron and chlorine had turned green as a result of the chemical reaction. In this instance, students indicated the mistaken... 

Extrapolation of Macroscopic Properties of Matter to the Submicroscopic Level... 

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