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# Tag Info

50

Substances which absorb almost all the light falling on them appear black. Therefore you are looking for the blackest known compound. The record is currently held by Vantablack[1], a substance composed of vertically aligned carbon nanotubes, which absorbs up to 99.965% of visible light incident upon it. As you can see it is really black. Previously, the ...

47

First, a little bit of background. Transparency is not an absolute property of a material. Every substance is opaque, so long as light has to pass through enough of it, and opacity also changes according to ambient conditions. Some substances, such as most metals, are opaque even in $100\ \mathrm{nm}$ thin films, while many gasses will let a small amount of ...

27

Definition of refractive index: $n=\frac {c}{v}$ If n>2 then this means that the velocity of light in the material is less than half than in vacuum so there must be a strong interaction with the material. One of the highest refractory index in liquids is 1.79(20°C) possessed by a solution of sulfur in methylene iodide($CH_2I_2$). Liquids are less dense ...

26

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 ...

25

Yes, $\ce{T2O}$ has been prepared and is available in significant quantity. When relatively pure, the energy released by the radioactive decay process is so intense that $\ce{T2O}$ will boil. It must be transported in a shielded, cryogenic dewar. A significant difference between compounds containing an element bonded to protium, deuterium or tritium is ...

22

All metals are capable of absorbing photons of any wavelength below hard ultraviolet, as ideally there are allowed electronic transitions of arbitrarily small energy between states in the unfilled valence band. This means metals are theoretically the materials with the widest wavelength range for photon absorption (except for plasmas). However, this comes ...

22

The analogy with a proton is actually a good one if you are careful to remember that an electron is nearly 2000 times lighter than a proton. What does that mean? It means that despite the fact that an electron is very "small", the electron is actually going to be very large because lighter particles will tend to spread out and have a much more diffuse ...

19

I'd separate transparent and colorless. Most gases are transparent or very nearly so because the concentration is low and absorptions are often weak. Chlorine, though is yellow-green, and has a noticeable color (from Wikipedia) Other halogens such as bromine and iodine do have observable colors as vapor, although as mentioned in the comments, you often ...

18

I used F'x answer as a starting point, and I found the mineral. It's called Ulexite. The fibers of ulexite act as optical fibers, transmitting light along their lengths by internal reflection. When a piece of ulexite is cut with flat polished faces perpendicular to the orientation of the fibers, a good-quality specimen will display an image of whatever ...

18

I'll try an answer to this question because I watched this video a while back and did a bit of reading on it at the time and I think I understand the big picture. The problem is that these solvated electrons are very complicated things, and do not lend themselves to the traditional ways that chemists would like to think about things. For that reason, there ...

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

The instrument used is called a polarimeter. You basically shine monochromatic linear polarized light through a solution of known concentration and you measure the rotation of the light on the other end of a tube with defined length. You then normalize the rotation according to concentration and length of your tube to get the specific rotation which is then ...

15

To complement @blu_potatos's answer, there are some other contenders having refractive index greater than 2 Arsenic di/trisulfide and sulfur and/or selenium and/or mercuric sulfide in arsenic tribromide solvent having refractive index ranging from 2.0 to 2.07 (arsenic tribromide seem to attack the lead-glass prisms of refractometers, corroding metal, ...

14

You have drawn the compounds correctly, and yes a solid wedge means the bond is coming out of the plane of the screen towards you a dashed wedge means the bond is going behind the plane of the screen away from you a solid line means the bond lies in the plane of the screen Here is a Newman projection of your molecules, sometimes Newman projections can ...

13

Any black compound absorbs photons in all the visible spectrum; that is why essentially it appears black to our eyes. So, for instance, iron(II,III) oxide, $\ce{Fe3O4}$ will do so; it is even used as a black pigment. It is very unlikely though that it will absorb each and every photon of any wavelength in the visible spectrum, but the search for such a ...

12

Conversion of D to L isomer or vice versa is about the last thing to worry about in this situation, even if it may be facilitated by sunlight to a significant extent (which I doubt). Also, storage of chemicals in dark coloured bottles is by no means limited to compounds that have optical isomers, or even to drugs in general. Other examples are numerous; ...

12

Good question. There's a phenomenon named cryptochirality[1] (meaning “hidden chirality”), when a compound, though chiral, has practically unmeasurable optical rotation activity. It can happen to molecules with chiral center(s) bearing very similar substituents. (So, no tricks with bonded slightly modified enantiomeric pairs are needed.) An example is 5-...

11

Isomerism is only one (and probably a minor) pathway. Many substances have chromophores that absorb light. Absorption leads to a high energy intermediate that is more reactive and able to access degradation pathways that were unavailable from the ground state. This is different from thermal excitation because the energizing photon carries a lot more energy ...

10

if optical rotation of optically pure 2-bromobutane is some (+X) degrees, will optical rotation of the product be some (-Y) degrees? No, there is no correlation between the configuration at a chiral carbon and the sign of optical rotation. For example (from the Aldrich catalogue), the following chiral bromo compound, (R)-(+)-2-Bromo-3-methylbutyric ...

9

Even though the central atom has 4 different ligands this does not necessarily mean that the compound is optically active. The condition for that rather the following (from Wikipedia): A molecule is achiral (not chiral) when an improper rotation, that is a combination of a rotation and a reflection in a plane, perpendicular to the axis of rotation, ...

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

This is something I discovered after an attempt at a more mathematically rigorous investigation of how to interpret polarimetry results. It's not that hard, but I don't think you'll ever find a similar analysis in a book because in practice the details are pretty much unnecessary for experimental purposes (though fun mathematically!). Before we begin, it's ...

8

My understanding is that it is an environment in which, when the isomers interact with the environment, the two enantiomers can be distinguished. That's exactly right. Some examples of chiral environments that could be created in a lab would include Running a reaction in a chiral solvent Running a reaction in a chiral cavity Running a reaction with a ...

8

$\ce{Co[(NH3)_4Cl2]}$ can exist as cis and trans isomers as shown in the following figure. image source If a molecule contains a plane of symmetry it cannot be optically active or chiral. In the cis isomer there is a plane of symmetry containing the $\ce{Cl-Co-Cl}$ atoms, therefore this isomer cannot be optically active. With the trans isomer there are ...

8

I'm not sure I understand what you want from the description above “transfer the letters”, but there is a typical high-school demonstration that I can think of that closely matches this description: that of birefringence.     Calcite (featured above) was the first material with which this effect was observed, in 1669, and still an easily obtainable ...

8

Mercury fulminate $\ce{[Hg(CNO)2]}$ can have a white, gray or greenish-brown color depending upon purity and dryness (it is often kept moistened to prevent accidental decomposition). Does fulminated mercury really have the translucent white/blue crystal appearance as was shown in this scene? I've never seen a picture where it appears translucent or ...

8

meso-compound A term for the achiral member(s) of a set of diastereoisomers which also includes one or more chiral members.[1, 2] isomer One of several species (or molecular entities ) that have the same atomic composition (molecular formula) but different line formulae or different stereochemical formulae and hence different physical and/or ...

8

Chirality refers only to the positions of the nuclei. So, if we have the situation you described where one Carbon is bonded to two other atoms (e.g. CX$_2$ or CXY) it can never be chiral. (i.e. a three atom molecule can always be superimposed on its mirror image by a single rotation) Now, why don't we consider the atomic and hybrid orbitals populations ...

7

If an atom is part of a double or a triple bond it is never a stereogenic center because then this atom and the atoms bound to it form something planar, so that you can always find a symmetry plane. But an atom that is part of a double bond can be prochiral, if it can be converted from to a stereogenic center in a single step.

7

There is no equilibrium in the second reaction because the sodium bromide formed by the iodide displacement is not soluble in acetone so there is no Br- to displace iodide. In contrast with the first reaction, NaI is soluble in acetone so there is always excess I- around to continue the reaction. This is called the Finkelstein reaction, further information ...

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