Crystallization teaching about

With regard to teaching about ions and ionic bonding Barke, Strehle and Roelleke [19] evaluated lectures in the sense of hypothesis two by the introduction of atoms and ions as basic particles of matter based on of Dalton s atomic model (see Fig. 5.10 in Chap. 5) scientific ideas according to chemical structures of metal and salt crystals are reflected upon. 

Racheli OK, let me begin then. After two demonstrations of the buzzing crystal of the common salt NaCl versus the non-buzzing sugar crystal, are you finally going to teach about ionic bonds ... 

Even though young people accept particles of matter in a discussion, difficulties always arise the particle concept is not consistently used. Helga Pfundt [6] demonstrated the dissolution of a blue copper sulfate crystal in water and, after teaching them about the particle concept in chemistry lectures, gave them a questionnaire asking about their ideas (see Fig. 4.7). 

Teaching and Learning Suggestions. The scientific particle term has to remain associated to the sub microscopic level, it should not be used for small portions of material. Of course, one can speak of iron filings, small sulfur crystals, tiny water drops or of little gas bubbles at this level it should be no problem to avoid the particle term when talking about matter. Students will thereby realize that the smallest particle is reserved for the invisible area of mental models of matter, i.e. water particles, sugar particles, and ethanol particles (compare Sect. 4.1). 

After a year he returned to Germany to teach and, as it turned out, to do the experiment that made him famous. The goal of the experiment was to prepare ammonium cyanate from a mixture of potassium cyanate and ammonium sulfate. He heated a solution of the two salts and crystallized the product. But the product didn t look like ammonium cyanate. It was a white crystalline material that looked exactly like urea Urea is a waste product of protein breakdown in the body and is excreted in the urine. Wohler recognized urea crystals because he had previously purified them from the urine of dogs and humans. Excited about his accidental discovery, he wrote to his teacher and friend Berzelius, "I can make urea without the necessity of a kidney, or even an animal, whether man or dog."... 

Sleutel, M., Maes, D., Van Driessche, A. (2012). What can mesoscopic level in situ observations teach us about kinetics and thermodynamics of crystallization ... 

Thanks to Prof. Paul Bernhardt for X-ray crystal data collection and for teaching me all about structure refinement. You became something like a third supervisor during these years. 

Symmetry considerations alone can teach a lot about the nature and properties of crystal orbitals. In a first approximation, each orbital in the unit cell can be considered as giving rise in k-space to a separate energy band, which may be vacant, half-filled or filled, as the original MO is, and whose width and slope can be qualitatively guessed on the basis of simple symmetry and overlap arguments. For example, in a row of n-stacked ethylene molecules the bands arising from s-a and p-a molecular orbitals must be very flat because of scarce or null overlap, while the n-n band would develop some width because of jt-overlap (Fig. 6.4). Since all the s and the p-n MO are fully occupied, so are also the s and the p-n bands, and the wide gap to the lowest unoccupied band, the p-n band, explains the insulating nature of this hypothetical material. 

Note that all of the parameters in Equation 4.2 are in the denominator, so if any of them go np, DP goes down. Since wavenumber units of cm are used in Equation 4.2, the DP calcnlated will be in centimeters multiply this number by 1(P to obtain DP in microns. At 1000 cm a diamond ATR crystal with n = 2.42, angle of incidence of 45 and sample refractive index of 1.4 (typical of many organic materials) gives a DP of 1.6 microns. Each of the parameters in Eqnation 4.2 has important things to teach ns about the ATR technique and its applications. 

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