# Tag Info

### Why are there exactly 5 types of two-dimensional lattices, and what distinguishes them?

First, about the black lines. I think they are helpful for the hexagonal and the rhombic lattice. For the hexagonal system, it shows you the hexagons. One hexagon contains exactly the same space as ...
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### Do superoxide salts of heavier alkali metals contradict the principle that lattice energy depends inversely on cation-anion distance?

TL, DR: They do not contradict. Although larger ions decrease the lattice energy by increasing ion distance, it is compensated by another factor that increases the lattice energy. And like Nisarg ...
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### Converting fractional coordinates into cartesian coordinates for crystallography

You have to use a matrix to convert. This is derived in most textbooks on crystallography, such as McKie & McKie 'Essentials of Crystallography'. The matrix is  M=\begin{bmatrix} a & 0 & ...
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### Do we really have technology with the resolution to distinguish between layers of single atoms of materials?

X-rays do not allow you to look at the material just like an microscope. You get the spacing information from the diffraction pattern of only crystalline materials and a lot of mathematics. On the ...
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### Why are there exactly 5 types of two-dimensional lattices, and what distinguishes them?

For the square, rectangular, and hexagonal lattices, the black lines show Wigner-Seitz primitive unit cells. They contain all points closer to a given lattice point than to any other lattice point. ...
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### Finding the atomic packing factor (APF) of Sodium Chloride and other FCC ionic compounds

Coming to question 1, that is, is your calculation correct? Quoting from Wikipedia, In solid sodium chloride, each ion is surrounded by six ions of the opposite charge as expected on electrostatic ...
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### Why sulfonate of detergent is less likely to bind to ions present in hard water than carboxylate?

Well. Solution of sodium alkylsulfonates are good detergents, because they produce calcium alkylsulfonates in hard water, and these calcium derivates are soluble in water. By contrast, usual soap ...
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### Hydrogen Bond Length and Lattice Density

Here is a sketch of a layer of ice: The hydrogen bonds are fairly short (177 pm, compared to a covalent O-H bond length of 100 pm), and the distance between hydrogen-bonded atoms is shorter than the ...
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### Why are there only 14 types of Bravais lattices and not 28 when there are 7 types of unit cells and each can have four variations?

Essentially, certain combinations of the possible point-group symmetries (cubic, tetragonal, hexagonal, trigonal, orthorhombic, monoclinic, triclinic) and possible translational symmetries (simple, ...
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### Why does density decrease when pressure is increased on an NaCl type lattice?

Two things to consider: Even though the sodium chloride crystal structure is face-centered cubic, it is not 12-coordinate. Face-centered cubic refers to the lattice formed by periodically equivalent ...
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### Why does density decrease when pressure is increased on an NaCl type lattice?

You've gotten a good answer from Oscar explaining the atomic details of what's actually happening. More broadly however, it is important to note that, irrespective of the atomic details, it's ...
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### Conventional unit cell for a hexagonal crystal system

Interestingly enough, the reason why the cell in bold is the unit-cell for the crystal is actually because the hexagonal cell has this higher symmetry you mention. To understand why, we have to ...
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### Conventional unit cell for a hexagonal crystal system

A crystal repeats contents of a unit cell in three dimensions. If you choose the unit cell to be a parallelepiped, the translation vectors are simply the edges of it. This is an easy way to describe a ...
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### Is there a standard scholarly reference for lattice constants of crystals of the elements?

The CRC Handbook of Chemistry and Physics contains a dedicated compilation by H. W. King, titled «Crystal Structures and Lattice Parameters of Allotropes of the Elements». In case your research ...
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### Unit cell structure of ionic crystal

I looked and there are a lot of questions on the site about units cells, many of which are pertinent. However I couldn't find one that answers your question directly. First there is no reason to ...
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### Radius ratio of octahedral interstitial site in BCC lithium

Actualluy it was a mistake. The impurities usually fall into the larger interstitial sites of crystal structures. According to this problem solving chapter, the interstitial sites in FCC and BCC ...
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### Why are there only 14 types of Bravais lattices and not 28 when there are 7 types of unit cells and each can have four variations?

Whether to use a centered cell or the smaller primitive cell is a question of convention. The conventions are guided by making life easy. You could take a primitive triclinic cell and redefine the ...
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### Explanation for the low melting point of zinc nitrate in terms of its lattice energy and electrostatic interactions?

Your melting point is not a melting point. Rather it represents the loss of water from a hydrate salt, which commonly occurs at much lower temperature than what would be required to actually liquefy ...
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