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Crystals have inspired a great many chemists because they are fascinating for a good reason. Not only are they aesthetically pleasing, but they serve as an excellent subject to tour a variety of theoretical subjects important for understanding high-level chemistry. Crystalline materials are made up of periodic structures. We’re only going to primarily focus ...


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There are four properties that make a diamond look like a diamond. I will compare them with the two best diamond simulants at the moment: cubic zirconia $\ce{ZrO2}$ - a special ("cubic") form of zirconium oxide. Don't confuse it with zircon, a different mineral with the forumula $\ce{ZrSiO4}$. moissanite $\ce{SiC}$ - the name for the naturally occurring ...


18

Are there other ways of "chemical strengthening" besides cationic exchange that can be utilized to strengthen the glass, keeping it flexible and less fragile at the same time? In a word: No. To understand why ion exchange strengthens glass, you have to understand why the ion exchange makes the glass harder. The process ion exchange hardening, its done at ...


17

Based on your comments, it sounds like you have some sort of colored sand and you want to immobilize it. My suggestion would be some sort of polymer matrix. There are multiple possibilities, but one of the easiest is polydimethylsiloxane PDMS which is optically clear and pretty easy to work with (i.e., safe). There's the "base" and a curing agent which ...


16

There are plenty of synthetic materials that would fall into the "cheap diamond equivalent" category. If we're only talking about the optical properties, cubic zirconia ($\ce{ZrO2}$) is probably the most familiar as it is often used in jewelry. It's index of refraction isn't quite as high and it's not as hard, but it's close enough that a fair amount of it ...


16

All quotes will be from Solid State Physics by Ashcroft and Mermin. Bravais Lattice: A fundamental concept in the description of any crystalline solid is that of the Bravais lattice, which specifies the periodic array in which the repeated units of the crystal are arranged. The units themselves may be single atoms, groups of atoms, molecules, ions, etc.,...


16

Short answer: Yes they do. Firstly, you need to arrive at a proper definition for an "object". Why you ask? Because it would otherwise present philosophical problems which become apparent when we begin to work with those objects. ... what is an object? Philosophers are always saying, “Well, just take a chair for example.” The moment they say that, you ...


15

The issue is one of yield. Each step has a certain yield percentage of yield, that the synthesizers will maximize as much as possible. However, given that it is fairly impossible to generate 100% yield all the time, the amount of desired protein you get over time will deteriorate exponentially with length. For example, say that each step gives you 95% yield....


13

$\ce{N5P3}$ is more commonly written as $\ce{P3N5}$, and known as triphosphorus pentanitride. It's a crystalline solid at ambient conditions and not a molecular compound. From the first publication that reported the pure compound and its structure [1]: In the solid a three-dimensional cross-linked network structure of corner sharing $\ce{PN4}$ tetrahedra ...


13

You need to perform one reaction per amino acid to couple it to the previous one, and that reaction isn't 100% efficient. You always get a small amount of unreacted peptide, or some other side product. Those small inefficencies add up for longer peptides because you're doing so many reactions. I created a quick graph showing the yield assuming 98% ...


12

Geologists prepare soil profiles for a living. The task is easy in principle - dig a pit, apply glue to the wall, then transfer the glued layer to a sheet of cloth. The practice is really difficult, the glue recipe and transfer technique are trade secrets. See here (warning, German language): http://www.sand-abc.de/sandkorn/lackprofil/lackprofil.htm Why ...


12

To calculate the height of a unit cell, consider a tetrahedral void in an hexagonal closed packing arrangement. It can be imagined as a 3 solid spheres touching each other and at the center-point, you have another sphere stacked over them. An interactive version can be viewed on this site. The situation looks like this: If you join the centers of these ...


11

There are two ways in which the band gap of a material: using optical spectroscopy and using electrochemistry. The way you go about analyzing the data to determine the band gap is independent of material, but the process of collecting the data is very specific to your material, and you should consult papers where others have made similar measurements on ...


11

I assume you meant amorphous solid phases, since you can always melt any ionic compound to form an essentially amorphous liquid phase. Googling "amorphous salts" brings up a fair number of results in the primary literature, such as this and this and this. The defining characteristic of such amorphous solid phases is that they exhibit no measurable melting ...


11

The difficulty with creating an ionic bond glass is that creating true glasses depends on a combination of directional bonding between atoms (or molecules) and a rate of cooling that doesn't give those bonds time to move into optimal positions. The result is a bit like piling together sticky spheres that become locked before they can find an optimal stacking ...


11

There are a few reasons, but the most direct answer is that the wavelength of X-ray photons is on the order of the distance between atomic nuclei in solids, e.g. ~ 4 ångströms (bonds are roughly 1.5-2.5 Å). You can think of it like the waves fit nice and snugly between the atoms and "fill" the crystal and thereby give us information about where the "cavities"...


11

External and internal pressure To study the effect of pressure on properties of a solid, is equivalently to learn how changes in volume transform physical parameters. For external pressure at constant temperature, this relationship manifests through compressibility $\kappa$. $$\kappa =-\frac{1}{V}\left(\frac{\partial V}{\partial P}\right)_T$$ An ...


10

If I'm reading your question rightly, I think the answer to your question is "geometry." That is, sodium and chlorine atoms form the particular structure of face-centered cubic because the relative size of the ions -- small for sodium large for chlorine -- makes that arrangement less stressful (energetically favorable). However, if you change the relative ...


10

I upvoted the water idea, after all it is possible to build sandcastles over 0.2 m high with just water as a binder. I also think coring as mentioned in that answer is a good idea. I also upvoted the comment about the freezer, although expansion could be an issue. I’m going to suggest a hot gelatine solution (or even dessert jelly just to try it out.) There ...


10

TL;DR Note that the passive layer forms on the surface, there needn't be any change to lattice constant. Chromium needn't migrate , the Cr present on the surface will form the layer to protect it. The key point is how the layer develops from say a single-atom layer of oxide to the usual/maximum width by migration of electron and oxygen in the oxide ...


10

An F-center (or any color center) is a point defect in the material that generates localized electronic states. When these states are in the band gap, they will result in strong peaks in optical absorption. An F-center in an alkali-halide material is an electron bound to a negative ion vacancy. A brief overview may be found in Ashcroft and Mermin's Solid ...


10

They signifies one polymorph (the beta polymorph) of barium zirconate. Allotropy is the property of some chemical elements or compounds to exist in two or more different forms, in the same physical state at different temperature. Now, technically they are the same element or compounds but have different crystal structure at changing temperature. So, in ...


10

To be precise, if in a close packed structure (ccp or fcc) there are $n$ atoms or ions then the number of octahedral voids and tetrahedral voids will be $n$ and $2n$ respectively. For example, there are 8 tetrahedral voids per unit cell of fcc structure $(Z_{\text{eff}}=4)$. If you divide the FCC unit cell into 8 small cubes then each small cube has 1 ...


10

The space radiation environment is a quite complex subject. Generally speaking one needs to be careful about just where in space you are concerned about - near earth orbit (within the Van Allen Belts), outside the belts, regularly passing through the belts, interplanetary, etc. That being said, the three main areas of concern are protons from the solar ...


9

Why do they degrade? What exactly is reducing their efficiency? This link outlines several modes of solar panel degradation, and this report by the National Renewable Energy lab is a very detailed review of studies on solar panel degradation worldwide. To summarize: Internal resistance of the cell can increase due to infiltration of contaminants (usually ...


9

If you had googled a little bit you would have found this wonderful resource. In a yellow diamond, a few carbon atoms per million have been replaced by nitrogen atoms, each containing five valence electrons. The structure of the diamond crystal does not change significantly, but the extra electrons occupy a donor level. The nitrogen donor level ...


9

In the gas phase ions cannot be stabilized through solvation or lattice forces so ions are destabilized relative to non-ionic entities in the gas phase. $\ce{NaCl}$ is a case in point, in the gas phase it exists as an equilibrium of monomers and dimers. Yet in the solid phase it exists as a highly ionic crystal. This example demonstrates that going from a ...


9

From Ashcroft and Mermin's Solid State Physics: A fundamental concept in the description of any crystalline solid is that of the Bravais lattice, which specifies the periodic array in which the repeated units of the crystal are arranged. The units themselves may be single atoms, groups of atoms, molecules, ions, etc., but the Bravais lattice summarizes ...


9

There is a bunch of such materials; among the elemental compounds, they include silicon, gallium, germanium, and bismuth. As for the properties... well, it just so happens that their crystal structure contains a little too much of empty space. Crystal packing is a tricky thing, it can't be predicted with certainty even with the most sophisticated methods.


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I'll just point out the direction in which you could look for an answer. In general case, it should be almost impossible to determine the crystal structure by looking at the chemical composition of a substance. You are, however, asked to explain why different fluorides adopt different structure types, which is a different task. Perhaps, you should take ...


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