In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid.

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Calculating Molar Volume from crystal volume

I am trying to calculate molar volume of certain crystal lattices to be used for crystal growth kinetics calculations. The information I have is the crystal volume & crystal lattices. For example ...
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Why is SiO2 solid while CO2 is a gas?

I was under the impression that chemistry almost exclusively involves valence electrons because there isn't enough energy to strip off electrons located closer to the nucleus. If that is true, and ...
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What bond\crystal has the most regular pattern (i.e. least irregularities)?

Salt is a famous regularly repeating cubic crystal, but there are always natural deformities and flaws present. I have heard that graphene is an extremely uniform substance. With these in mind, what ...
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Pyramid Structure Name

I would like to know what the name is for the structure drawn below. This looks like a pyramid with 4 atoms at each vertex. Does the name of the structure depend on whether the atoms are all the same ...
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data repository of organic compounds

Does there exist any data repository of chemical compound that gives the structure of the compounds with the help of coordinate geometry. It would be like each atom has a coordinate and the list of ...
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Solidification of sodium polyacrylate

Sodium polyacrylate is a white powder with a characteristic odor. But when we add water to this powder, instead of forming a aqueous solution , it instantaneously solidifies and forms more amount of ...
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Number of atoms in NaCl

Consider this picture of an $\cf{NaCl}$ unit cell: It appears to show 14 $\cf{Cl-}$ ions and only 13 $\cf{Na+}$ ions. Given that discrepancy, how is table salt balanced for charge? Why isn't ...
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26 views

Extracting “Crystal Radii” from a CIF file

I'm currently downloading .cif files from various online databases and using openbabel to convert the fractional coordinates that are in the .cif files into .xyz files. The typical output will look ...
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What are the structures of potassium superoxide and xenon hexafluoride? [closed]

I have 2 questions in mind: 1) What is the structure of the superoxides? More specifically, what is the structure of $\ce{KO_2}$? 2) What is the structure of and dipole moment for $\ce{XeF_6}$?
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55 views

Finding large databases of sphere packings

Part of my research is investigating sphere packings and their properties.I really would like a large database of sphere packings that I could investigate using a program I have written that tells me ...
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43 views

Are there any early industrial age methods capable of determining diamond or graphite's crystalline structure?

I'm writing a fictional story with early industrial age technology where a chemist discovers not only that diamond and graphite are made of the same substance, but that they differ by crystalline ...
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Elements of symmetry [duplicate]

Which are the elements of the Twofold Screw Axis 2/3 in this image (green line)? The blue Dots (1/3- and +)?
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R32 Space Group

Which are the elements of the Twofold Screw Axis in this image? The "+" and "-" elements that intercept the red line are the elements of the Twofold Screw Axis 2/3? And if so, is the height of the ...
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Real space term for PPPM vs PME

I was under the impression that differences between the various long range electrostatic algorithms, ewald, PME, PPPM, to name a few, lied solely in their treatment of the reciprocal space term. ...
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Shapes of ionic compound

Can anyone explain the shapes of ionic compounds? What does it mean? What does the coordinate number mean? I know that in $\ce{NaCl}$, one $\ce{Na}$ atom is surrounded by 6 $\ce{Cl}$ atoms, and vice ...
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41 views

What determines the elastic limit of a substance?

from what I know, the elastic limit of a substance is the maximum amount of stress/force/pressure (a bit of confusion on my behalf here) a substance can withstand and still return to its original ...
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What factors contribute most to solubility of ionic substances in highly polar solvents, esp. ionic liquids and DES?

I am trying to determine a method to dissolve a mineral salt with a lattice energy of ≈18000 kJ/mol. I know that lattice energy is the most significant factor affecting solubility of an ionic ...
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493 views

Why are so many ionic compounds brittle?

Even when ionic compounds are strong (e.g. rubies and sapphires), they are neither malleable nor ductile in the slightest, and if sufficient stress is put on them, they will shatter, not bend. Why is ...
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149 views

What is the difference between an amorphous solid and glass?

They are both formed when a liquid is supercooled rapidly, no free energy, and they both have irregular structures. What defines a glass other than how it is amorphous, transparent, and has a glass ...
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R32 Space Group (Crystallography)

Why R32 Space Group is so named? I mean, if R stands for Rhombohedral and 3 for Threefold Axis, what 2 stands for? I don't see any Twofold Axis in the cell: ...
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Do Crystals have stronger intermolecular bonds than amorphous solids?

Do Crystals have stronger intermolecular bonds than amorphous solids and are the properties of amorphous solids vs. crystals explained by their structures?
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Finding Ice CIF files in crystal database

Could anyone please tell me where I could find the the structure of cubic ice (ice Ic) as a .cif file? I have been searching the cambridge structural database using "H2O", "water", "dihyrogen oxide" ...
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How to compute the NMR shift in Gaussian09 for only one specific atom in a bigger unit cell?

I am trying to compute the NMR shift for a specific atom in the middle of the surrounding crystal unit cell (1 surrounding anion sphere and 1 cation sphere) in Gaussian09. I only need the chemical ...
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How are piezoelectric crystals made?

I want to know how the powdered formed of piezoelectric material is converted to crystal like used in quartz watches. I know that some more chemicals are mixed with the material and then it is pressed ...
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147 views

How to add hydrogens to a crystal structure

PDB protein crystal structures most of the time lack hydrogen atoms. Usualy I use PyMOL (h_add) but it does not always seem to be giving the correct result. What ...
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What is omega and nu in this expression?

In the picture below a proportionality equation is shown: $$\omega \propto \nu \exp\left(\frac{-\Delta G_m}{RT}\right)\propto \dots$$ While $\Delta G_m$ is the Gibbs free energy, $R$ is the gas ...
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Why do some crystal structure files not include bonds?

Why do some crystal structure files not include bonds (the atoms are just placed in the respective position in the cell without bonds between any atoms)? Shouldn't the bonds always be there? Also, ...
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Deformation of the nematic phase of liquid crystals surviving in the solid state

Does anyone know if I were to cool a liquid crystal with a deformed nematic phase quickly, if it will preserve the deformation in the crystal lattice? I didn't find any information in classical ...
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How would one construct a 3D model of a molecule based on the crystal structure of its salts?

Often crystal structures found online from past published crystallography experiments are of the salt of a molecule of biologic interest, as opposed to the freebase form of the molecule itself. For ...
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What things form crystals? [closed]

Just getting interested in this stuff. People are saying I should crystallize salt, for example. What things could I do instead of salt with and still get a crystal from? Thanks a ton!!
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Crystal field theory for calculating lattice parameters

If I have an 8-coordinated metal cation (e.g., $\ce{Te}$, $\ce{Nb}$, $\ce{Ta}$, $\ce{Sb}$, $\ce{Bi}$, $\ce{Zr}$, $\ce{Hf}$) by oxygen anions, is there a way to theoretically calculate the structure of ...
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Can bone mineral be obtained in pure, crystalline form?

Can bone mineral be obtained in pure, crystalline form outside a living organism? Had this been done ever?
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Structure of Ca2B6O11

What is its structure? I found an image of $\ce{B6O11}$ unit but it looks incorrect: The top left corner one. The oxygen can make max 2 bonds but $\ce{O8}$ has three! There are six ...
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How to determine the Bravais lattice and atom basis vectors from a CIF file?

Say I have a CIF file describing some material in terms of its symmetry space group, lattice parameters and in-cell atom positions. A simple example might be, ...
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Modified DNA bases in Pymol and Coot

When using Pymol or Coot molecular visualization software to solve x-ray crystallography structures, how can I mutate a cytosine to a 5-methylcytosine?
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Theoretical Calculation of Lattice Parameter from Space Group

If I am given a compound which belongs to, say the cubic $\text{Ia}\bar 3\text{d}$ space group, is there a known way to calculate the lattice parameter of the compound? In general, can lattice ...
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How to predict if hydrogen atoms could be placed in the interstials of a lattice

Palladium hydride is an example of a hydride which contains H atoms in palladium's crystal lattice (which is fcc). I would like to know if it's possible to predict if another hydride, $\ce{NbH_{x}}$ ...
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Determining structure factors for crystals from lattice and motif

I understand that the structure factor for a crystal is given by: $$F_{hkl} = \sum_r f_{r} e^{2{\pi}i(hx_{r}+ky_{r}+lz_{r})} $$ My textbook (''Structures of crystals'', Glazier) suggests that you ...
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Why is sand/glass polar? How does lattice structure change polarity?

The molecular geometry of sand is linear. Dipole moment is thus cancelled. But we all know from the meniscus water makes with glass that the dipole-dipole/H-O attraction between sand and water is ...
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Can chemicals change crystal structure by only touching?

Are there any known, or suspected compounds that take the crystal structure of what ever object they are touching, i.e. if it touches $\ce{NaCl}$ it would turn into a face centered cubic crystal ...
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Is there any required data missing from my CIF file?

I previously asked a question about a CIF file here (namely CIF fields that are available for some atoms, but not others) I think I have the answer (namely to place dots [.] at places where the two ...
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CIF fields that are available for some atoms, but not others

I've been working on another CIF file, this time for (-)-threo-methylphenidate based on Pharma Res, 1995 (sadly the relevant crystallography data isn't supplied in the free preview at Springer). I ...
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Azathioprine CIF data file rendering problem in Accelrys

I have been working on a CIF data file (URL: http://goo.gl/2cprI6) based on data from this experiment: Acharya, 1984 (free full text isn't available, but the page [page 2] with the experiment details ...
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How does the atomic structure of crystals determines its shapes? [duplicate]

for example, table salt has an a cubic structure in the atomic level, and they are often cube like in the visible level. I don't see any reason that the atomic crystal structure should reflect the ...
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568 views

Why does pyrite form cubic crystals?

Pyrite ($\ce{FeS2}$) forms cubic crystals, like these ones: I know that the crystal structure is primitive cubic, but I don’t see how cubic structure on the molecular level translates to cubic ...
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When does hydrogen bonding happen?

What kinds of molecules will experience hydrogen bonding (inter and intra)? Why does it occur for some H atoms but not others?
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198 views

What is a catemer?

What is a catemer and how does it differ from a dimer? What type of compounds could form catemers and how does their formation influence its crystal structure?
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Coloration of substances because of F-Centers

In case of metal deficient defects in the crystal lattice of a metal, the positive voids are filled by electrons. How does this result in the coloration of a substance? Does this condition arise ...
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Unit cell of CdCl2

I understand that $\ce{CdCl2}$ has a rhombohedral unit cell as shown in this book. However I often find it being referred to as a "CCP analogue" of $\ce{CdI2}$. Presumably it is the chlorides which ...
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Is Polymorphism accompanied with an energy change?

Differential Scanning Colorimetry (DSC) is a technique used to identify Polymorphism by revealing two melting points of a pure crystalline structure. DSC shows a peak associated with the formation ...