Submicroscopic properties

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. 

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). 

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. 

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

The extrapolation of physical attributes of substances to the submicroscopic level of representation was evident when students explained the changes in the displacement reaction between zinc powder and aqueous copper(II) sulphate. The decrease in intensity of the blue colour of the solution was attributed by 31% of students to the removal of blue individual Cu + ions from aqueous solution. The suggestion that individual Cu + ions (the submicroscopic level) are blue may be indicative of the extrapolation of the blue colour of the aqueous copper(II) sulphate (the macroscopic level) to the colour of individual Cu + ions (the submicroscopic level). Thirty-one percent of students also suggested that reddish-brown, insoluble individual atoms of copper were produced in this chemical reaction, again suggesting extrapolation of the bulk properties of copper, i.e., being reddish-brown and insolnble in water (the macroscopic level), to individual copper atoms having these properties (the snbmicroscopic level). 

Micelles and vesicles can also be used in the preparation of very small submicroscopic particles which may be useful as heterogeneous catalysts or because of their properties as semiconductors (Lufimpadio et al., 1984 Tricot and Fendler, 1984). 

It is a fundamental problem to predict the shq>e that a crystal will adopt when growing firom a submicroscopic nucleits to its macroscopic form. Generally, both the intririsic properties of the crystallizing matter and the external conditions (supersaturation, temperature, etc) will effect the shape. 

The familiar bulk properties of a solid, liquid, and gas. (a) The submicroscopic particles of the solid phase vibrate about fixed positions, (b) The submicroscopic particles of the liquid phase slip past one another. 

In this chapter we explored many of the rudiments of chemistry, including how matter is described by its physical and chemical properties and denoted by elemental and chemical formulas. We saw how compounds are different from the elements from which they are formed and how mixtures can be separated by taking advantage of differences in the physical properties of the components. Also addressed was what a chemist means by pure and how matter can be classified as element, compound, or mixture. Lastly, we saw how elements are organized in the periodic table by their physical and chemical properties. /Jong the way, you were introduced to some of the most important key terms of chemistry. With an understanding of these fundamental concepts and of the language used to describe them, you are well equipped to continue your study of nature s submicroscopic realm. 

Why do halite crystals have such a distinct shape As we explore in this chapter, the macroscopic properties of any substance can be traced to how its submicroscopic parts are held together. The sodium and chloride ions in a halite crystal, for example, are held together in a cubic orientation, and as a result the macroscopic object we know as a halite crystal is also cubic. 

This chapter explains how many of the physical properties of materials are a consequence of attractions among the submicroscopic particles making up the materials. Why only small amounts of oxygen can mix with water, for example, can be explained by the fact that the attractive forces between water molecules and oxygen molecules are very weak. We begin by looking at four types of electrical attractions that occur between submicroscopic particles. 

Taneya, S., Kimura, T., Izutsu, T., Buchheim, W. 1980. The submicroscopic structure of processed cheese with different melting properties. Milchwissenschaft 35, 479—481. 

The submicroscopic emulsion polymerized form of IPN s would be expected to differ in mechanical properties from the counterpart bulk polymerized form in that (1) The latex particles are not crosslinked one to another allowing movement of one latex particle past another. (2) In bulk IPN s (10) it was shown that polymer I forms the continuous or more continuous phase while in latex IPN s polymer II tends to form the more continuous phase (1). 

There are reports of the use of iron species as probes (chemisorbed species) to characterize supports and their adsorption properties. Burger et al. (200) used Mossbauer spectroscopy to characterize submicroscopic droplets of Sn(IV) and Fe(III) complexes carried in an alkane/naphthalene mixture. The analysis of the Mossbauer parameters gave a qualitative picture regarding the solution structure inside the pores and the adsorption and wetting properties of the solid. 

Bale HD, Schmidt PW. Small-angle X-ray-scattering investigation of submicroscopic porosity with fractal properties. Phys Rev Lett 1984 53 596-599. 

With the advent of modern atomic theory began a new major enterprise in the science of chemistry that of understanding the bulk properties of materials in terms of the properties and machinations of their component submicroscopic atoms and molecules. The enterprise moved very slowly into its current central role in the science of chemistry. Atomic theory won acceptance among chemists only slowly and, in many quarters, grudgingly. Antiatomist views were common among chemists into the late nineteenth-century, and agnostic views persisted until well into the twentieth (e.g.. Smith, 1910, pp. 224-225), despite the experimental work of Thomson, Rutherford, and other physicists on the structure of the atom. 

Friedrich, P. (1984). Supramolecular Enzyme Organization, Pergamon Press, New York/Oxford. Luby-Phelps, K., Latuii, F., Taylor, D. L. (1988). The submicroscopic properties of cytoplasm as a determinant of cellular function. Atm. Rev. Biophys. Biophys. Chem. 17,369-396. 

In the same way, the appearance and properties of a piece of matter are the result of its structure. Although you may get hints of the actual structure from a macroscopic view, you must go to a submicroscopic perspective to understand how the hidden structure of matter influences its behavior. 

Chemistry is often iike detective work. To figure out the submicroscopic structure of a compound, you first have to examine some of its macroscopic properties. Just as no two human fingerprints are the same, no two substances have exactiy the same combination of physicai and... 

The chemical properties of sodium chloride are not so useful in our detective work to determine its submicroscopic structure. Salt does not react readily with other substances. It could sit in a salt shaker for hundreds or even thousands of years and still remain salt. It does not have to be handled in any special way or be stored in a special container. Compounds with these chemical properties are referred to as stable or unreac-tive. You can get more clues about salt s submicroscopic structure by answering the question How do the properties of salt compare with the properties of its component elements, sodium and chlorine ... 

You ve seen that elements combine to form compoimds whose properties differ greatly from those of the elements themselves. Figure 4.9 shows another example. On the submicroscopic level, this clue indicates that atoms of elements react chemically to form some combinations that are much different from the original atoms. Also, if atoms of elements always combined in the same way, it s likely that aU compounds would be similar. However, you ve just studied three compounds that have greatly dilfering properties. On the submicroscopic level, this clue indicates that atoms must be able to combine in different ways to form different kinds of products. With the knowledge of the structure of atoms that you learned in Chapters 2 and 3, you can now examine the different ways that atoms can combine. 

Now you can relate the submicroscopic models of the formation of NaCl, H2O, and CO2 to their macroscopic properties mentioned in Section 4.1. When elements combine, they form either ions or molecules. No other possibilities exist. The particles change dramatically, whether they change from sodium atoms to sodium ions or hydrogen and oxygen atoms to water molecules. This change explains why compounds have different properties from the elements that make them up. 

As with ionic compormds, the submicroscopic model of the formation of covalent compormds explains many of the properties of these compounds. In particular, you can use this model to explain why typical covalent compounds such as H2O and CO2 have properties so different from ionic compounds. 

What are three general properties of ionic compormds How are these properties related to the submicroscopic structure of the com-poimds ... 

Recall from Chapter 4 that the submicroscopic structure of ionic compounds helps explain why they share certain macroscopic properties such as high melting points, brittleness, and the ability to conduct electricity when molten or when dissolved in water. What is it about the structure of these compounds that gives them properties such as the one shown in Figure 5.1 The answer involves the ions of which they are made. 

How does the submicroscopic structure of molecular substances contribute to their macroscopic properties Because there are no ions, strong networks held together by the attractions of opposite charges do not form. The interparticle forces between molecules are often weak and easy to break. These weak forces explain the softness and low melting points of most molecular substances. Most molecular substances are not electrolytes because they do not easily form ions. 

The atomic theory evolved over a period of 2000 years. But it s the experimental evidence of the last 200 years that reveals the complex nature of the submicroscopic world. Because electrons are responsible for an element s chemical properties, chemists need an atomic model that describes the arrangement of electrons. 

When you compare the physical properties of the polar molecule water with the nonpolar molecule methane, you see major differences. Although water and methane are approximately the same size and both are covalently bonded, water is a liquid at room temperature, whereas methane is a gas. Table 9.2 shows a comparison of the melting points and boiling points of water and methane. Notice that the boiling point of water is 264°C higher than the boiling point of methane. This is macroscopic evidence for the submicroscopic attractions at work among water molecules. 

Recall from Chapter 4 that the submicroscopic interactions between the particles of a substance determine many of its macroscopic physical and chemical properties. For ionic compormds, the strong attractive force that binds positive and negative ions into well-ordered crystals keeps the physical properties of ionic substances to a relatively narrow range of variability. 

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