35 votes
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Contribution of Tetrahedral and Octahedral voids in HCP

I cannot find anywhere.. Couldn't find? You can figure it out on your own, with me, right now. Disclaimer: By "hexagonal unit cell" I assume you mean hexagonal prism, which comprises of 3 primitive ...
William R. Ebenezer's user avatar
24 votes

Why are Silicates solid while carbon dioxide is a gas?

The reason why carbon dioxide is a gas and silicon dioxide is a solid is because their chemical structures are different. Carbon dioxide is a linear structure with two double bonds between carbon and ...
matt_black's user avatar
23 votes
Accepted

Why is the buckminsterfullerene the purest form of carbon?

Diamond has dangling bonds on the outer surface of the crystal for pretty much the same reason as graphite. If you understood graphite differently, then you understood it wrong. See, a molecule of ...
Ivan Neretin's user avatar
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20 votes
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What is the smallest molar volume?

Boron is a covalent solid with high melting point, like diamond (though not quite), and hence its crystals are hard to make. Unlike diamond crystals, they are not nice and probably wouldn't make a ...
Ivan Neretin's user avatar
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20 votes
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Why use diamond-like carbon instead of diamond?

You balance cost of manufacture and return of investment for the anticipated use. If you read about the methods of production of diamond-like carbon (DLC), e.g., on Wikipedia, e.g. «DLC is typically ...
Buttonwood's user avatar
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17 votes

How to calculate the height of an hcp lattice?

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 ...
Berry Holmes's user avatar
  • 4,134
16 votes

How are the number of tetrahedral voids twice the number of octahedral voids in a CCP structure?

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 ...
Mitchell's user avatar
  • 1,108
16 votes
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For a given packing (hcp, fcc, bcc), which ions occupy the corners and which occupy the faces or centers?

The actual answer is that it doesn't matter. For many of the 1:1 solid-state structures, either the cations or the anions may be considered to be at the vertices (i.e. corners) of the unit cell. By ...
orthocresol's user avatar
15 votes

Conception and manufacture of the Avogadro Project's (nearly) perfect silicon sphere (and, what is “atomic feeling”?)

Short answer: The success of the project benefitted from many contributors. According to BIPM and its Avogadro project, there are two spheres (reference). The page equally refers to a publiction ...
Buttonwood's user avatar
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14 votes
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Why can a face-centered cubic lattice not be redrawn as a body-centered tetragonal lattice?

OK, let's get it straight. A lattice is just a periodic set of points. For the sake of brevity, I'll talk about 2D lattices; trust me, with 3D it is pretty much the same, only more complicated. ...
Ivan Neretin's user avatar
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14 votes

Why does this lysozyme powder not look crystalline?

The typical protein crystal does not withstand mechanical stress equally well than e.g., the ones of table salt, or refined sucrose. Hence the varying shapes of grains. Photos about nice protein ...
Buttonwood's user avatar
  • 29.7k
13 votes

What does β stand for in β-potassium zirconate?

They signify 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 ...
Nilay Ghosh's user avatar
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13 votes
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A unit cell for graphene

The unit cell for graphene is a two-dimensional rhombus according to the figure shown on page 31 of this paper.$^1$ (also here.) The result is that two atoms are contained per unit cell. The upper ...
Xahoc's user avatar
  • 918
13 votes
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Distinguishing between octahedral and tetrahedral holes

To visualize holes in closest packing of spheres, you need 6 balls (marbles, table tennis balls, etc) of equal size. 3D closest packing can be constructed from 2D layers of closest packed spheres as ...
Karsten's user avatar
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12 votes

Dihedral angle of gaseous and crystalline HOOH

In an attempt to improve the given answer and also address other issues in the discussions of other duplicates of this question, I have optimised (PBE-D3/def2-SVP using NWChem 6.6) the $\ce{H2O2}$ ...
schneiderfelipe's user avatar
12 votes
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Image of crystal structure

I recommend to fetch the crystal structures of inorganic compounds via specific Google search pattern site:crystallography.net <keyword(s)>, e.g. in your case ...
andselisk's user avatar
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12 votes
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How to understand the chemical formula of Prussian blue complex w.r.t its crystal structure?

The structure of Prussian blue is not as regular as Jonas thought. It is basically cubic as Jonas has drawn. But Jonas's figure includes the same number of $\ce{Fe^{II}}$ as $\ce{Fe^{III}}$, which is ...
Maurice's user avatar
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11 votes
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Why are X-rays used in crystallography?

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....
khaverim's user avatar
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11 votes
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What is this blue crystal?

As orthocresol also mentioned, it's probably copper sulfate. As you said, the blue color essentially gives it away. (picture taken from Science Madness Wiki)
Glorfindel's user avatar
  • 2,075
11 votes

Calculating the theoretical Density of a Lithium oxide

Here's the unit cell of $\ce{Li2O}$, which adopts an antifluorite structure. The image is adapted from this webpage; technically it shows the fluorite structure but it doesn't matter. The cation-...
orthocresol's user avatar
11 votes
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Miller Indices: How to deal with some weird(-ish) cases?

IFF I remember correctly... Sometimes you have to "move" the plane, in order to see where the axis crosses. Take example 7, if you look at the example plane, the one actually shown, it is (0 ...
Stian's user avatar
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11 votes
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What would oxygen or nitrogen snow look like?

I don't know if there would actually be oxygen and nitrogen snow. I would think under those circumstances, there might be carbon dioxide snow, but the rest of the atmosphere would probably liquify ...
Gwyn's user avatar
  • 737
10 votes
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Why alkali metals have bcc structure?

For the moment I will focus on Na, although I may mention other elements in comparison. First, it is true that the STP stable phase of Na is bcc. However, the energy difference between the bcc, fcc, ...
Jon Custer's user avatar
  • 8,509
10 votes
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How many crystal forms of HCl have been identified - where to find the unit cells/lattice constants?

From the first picture depicted, I would refrain from stating there are five HCl molecules per unit cell. One thing, while there is some choice in the definition of a unitcell (there are several ...
Buttonwood's user avatar
  • 29.7k
10 votes

How thick is a snowflake?

There are many different types of crystals and their fromation is far too difficult for me to understand. This answer simply deals with the thickness part and that too merely gives a rough ...
Avyansh Katiyar's user avatar
10 votes
Accepted

How can I get xyz coordinates of atoms of a unit cell structure from CIF format files?

CIF contains coordinates for the atoms in asymmetric unit only (what Ivan called "the independent part" in the comments), plus the set of symmetry operation to fill the remaining space with ...
andselisk's user avatar
  • 37.6k
10 votes
Accepted

Conception and manufacture of the Avogadro Project's (nearly) perfect silicon sphere (and, what is “atomic feeling”?)

First thing I think we have to differentiate between checking the roundness and the roughness (that in the article seems it is called smoothness) these two properties of the surface necessitate ...
G M's user avatar
  • 9,069
10 votes

Why use diamond-like carbon instead of diamond?

Why do you think that would be preferable? A perfect crystal is rather fragile - diamonds are hard, but they also have perfect cleavage - one good hit and you have two diamonds (or a bunch of shards). ...
Luaan's user avatar
  • 505
9 votes

Why are there no hydrogen atoms in the crystal structure of a biomolecule?

Typically crystal structures are determined by X-ray diffraction off of electrons within a bond and around the nuclei of each atom. Since H only has 1 electron, and its often involved in a polar type ...
StevieD's user avatar
  • 631
9 votes

What does β stand for in β-potassium zirconate?

Some inorganic crystals show the property of structural polymorphism where two or more crystal polymorphs exist. These polymorphs may differ either by position of metal ion or ligand (or other ion ...
ankit7540's user avatar
  • 1,582

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