37 votes

Carbon atoms at the edge of a diamond

Atoms at the edge of a crystal that have an unsatisfied valence are said to have "dangling bonds." Many elements, in addition to carbon, can have dangling bonds. Dangling bonds is a subject of ...
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28 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 ...
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26 votes
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Why is sand, sand; and why is glass, glass; While both mainly contain Silicon Dioxide?

Is it crystallization? You are correct. The main difference is that sand is crystalline and glass is not—it is amorphous. The main component (> 95%) of common yellow sand is quartz (the mineral ...
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  • 5,004
23 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 ...
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22 votes
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Are metallic/ionic bonds weaker than covalent bonds?

Quartz and diamond are stronger substances because their molecules form network covalent structures. These structures form a lattice-like structure, much the same as ionic compounds. This molecular ...
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22 votes
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Why is it that every snowflake is unique?

It turns out that 2 identical snowflakes have been observed, but... Two Identical Snowflakes Although when we think "snowflake" we usually picture an object with 6-fold radial symmetry, snowflakes ...
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22 votes
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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 ...
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20 votes
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Why are there only 7 types of unit cells and 14 types of Bravais lattices?

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 ...
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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 ...
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19 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 ...
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18 votes

Carbon atoms at the edge of a diamond

You asked a question, belonging to surface chemistry. It is a relatively new area of research, as it relies heavily on atomic-resolved microscopy and computational methods. Generally, the answer ...
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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 ...
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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 ...
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15 votes
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Why are so many ionic compounds brittle?

Ionic crystals are hard because of tight packing lattices, say, the positive and negative ions are strongly attached among themselves. So, if mechanical pressure is applied to an ionic crystal then ...
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15 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 ...
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  • 1,098
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 ...
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14 votes
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Is BCl₅ possible?

Boron pentachloride is likely not stable except perhaps in extreme conditions, such as under very high pressures. Even then it may be possible that a description such as $\ce{[BCl4^{-}]Cl^+}$ ...
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14 votes

Number of atoms in NaCl unit cell

The picture you showed does have an unequal number of sodium cations and chloride anions. However, the picture shows only part of a crystal. Every atom that is on a boundary of the shown cube, ...
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13 votes
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What are these crystals on my champagne cork?

They are potassium bitartrate crystals (source). The crystals form because the potassium bitartrate is not very soluble. Since solubility is a function of temperature, when wine is chilled the ...
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13 votes
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Dihedral angle of gaseous and crystalline HOOH

You've already answered your own question - hydrogen bonding. First, don't think of it as to why is the gas state different than solid-state. Rather, think about why is the solid-state different than ...
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13 votes
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What is a catemer?

In the crystal, carboxylic acids mostly form dimers through pairs of $\ce{OH\bond{~}O=C}$ hydrogen bonds. In some cases, infinite chains of hydrogen bonds are formed instead: here, each carboxylic ...
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13 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. ...
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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 ...
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12 votes
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If salt crystals make a cube shape, what is this 'X' marking?

When salt (NaCl) crystals are grown under normal conditions, the edges of the cubes usually grow faster than the faces (because the edges have more contact with the saturated salt solution than the ...
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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 $\ce{H2O2}$ ...
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12 votes

What does β stand for in β-potassium zirconate?

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 ...
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12 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 ...
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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 ...
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11 votes

If salt crystals make a cube shape, what is this 'X' marking?

Let's look at structure of $\ce{NaCl}$ ideal cubic crystal As you can see, atoms on the faces have 5 neighbors, atoms on the edges has four neighbors, and atoms on the vertices of the cube have 3 ...
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