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semiconductive
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| Quote: | | That may be the physicist's definition of a metal, but a chemist defines a metal as an element that tends to lose electrons to form cations when it
reacts with a nonmetal. Hydrogen, unlike sodium, lithium, etc, does not form simple cations, and always forms either molecular compounds, or becomes
part of a covalently bonded polyatomic cation. So sodium, lithium, potassium etc. all act like typical metal ions in solution, whereas hydrogen shows
very different behavior. |
OK. Another background issue. Tomato, Tamatoe.
| Quote: |
In the case of hydrogen, it uses its 1s orbital for bonding. For the alkali metals, apart from very rare compounds such as methyllithium, their
bonding is almost purely ionic, and they don't use orbitals for that- just cation attracting anion.
[Edited on 25-1-2018 by DraconicAcid] |
The difference between an ionic bond and a covalent bond, quantum mechainically, is usually one of degree and not kind. Every time atoms come
together there are filled orbitals/ stationary states, and unfilled orbitals/stationary states. AKA, the so called "bonding" and "anti-bonding"
orbitals. But any actual motion of a wave-particle requires the superposition of two or more states. Therefore, any time atoms are in thermal motion
.. multiple quantum states are involved.
Some people think that when an atom vibrates due to thermal agitation, the electrons are promoted for brief periods of time into the lowest
anti-bonding orbital. Others think the orbitals split. So, it's an over-simplification to say that all the alkali-metals are purely in an ionic
state. Atoms somehow share electrons in proportion to the vibrations and tunneling occurs a fair number of times a second. I mean, E=hf can be
applied to the bonding energy of two atoms as well as to the wavelength of a moving electron. So, if you tell me a bonding energy -- I should be able
to compute a vibration frequency for the two atoms around a center of mass, or "barycenter." as relativity buffs like to correct me when I use the
older term; and show how often the electrons go around the counter-ion. It's a non-zero probablity.
Is this why the drawing you showed me from wikipedia has hydroxide (OH) ions with no bonds being shown to any other nearby atom? They are making some
kind of hard distinction between ionic bond and covalent bond???
I've heard and seen chemistry where resonance effects are going on. In older texts, that was usually shown by a dotted line where a bond switched
from one atom to another. Indeeed, in the pictures of Citric acid one such bond is shown between the two OH radicals. The same type of bond is NOT
shown in the case of glucose.
But I have never seen someone draw an oxygen atom having three bonds ... like the picture you showed me from Wikipedia. And no, I've never heard of
the ion you asked me about.
We just treated ph as H+ and OH- in solution. Since Oxygen has already been satisfied with two hydrogens donating electrons to the shells; I would
think a third hydrogen was merely a resonance effect where it time shares bonding to the oxygen with other hydrogens. I don't see why you couldn't
have a fourth hydrogen, making a H4O++ ion, though it would be even less stable than the so called hydronium ion.
But I don't see what concept is important when the hydronium ion idea was made. In fact, every time a water molecule with an extra hydrogen tagging
along randomly bumps into another water molecule -- it's equally likely that a hydrogen will transfer from one water molecule to the next. The
"thrid" hydrogen isn't stuck to any given hydronium molecule electrostatically more than another water molecule. I would think it's bond energy
would be indentical with all water molecules ... shrug ...so it effectively wanders freely (or makes the whole hydronium "molecule" unstable so that
each of the hydrogens is temporally equally likely to wander away from the hydronium ion). I don't see how it's more advantageous than earlier
resonance line drawings of water...
[Edited on 25-1-2018 by semiconductive]
[Edited on 25-1-2018 by semiconductive]
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DraconicAcid
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Quote: Originally posted by semiconductive  | To be fair to the author, he did not make a mistake that was reducing the issue to water alone. Neither did I intend to imply that only water was
involved in color making. The paper clearly states that the hue of "blue" changes when ammonia is the solvent instead of water. Therefore, even this
ancient author gives an example proving they knew that color depends on kind of ligands and well as number.
|
When he talks about ammonia, he does say this, but when he's talking about various chlorides (i.e., copper(II) chloride and mixed salts with cadmium
and other chlorides), he does dismiss the chlorides and speaks only of the number of water molecules. I wasn't suggesting that you were implying
anything.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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semiconductive
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| Quote: Originally posted by Σldritch | | Reducing sugars are reducing because they can become aldehydes in solution. Ascorbic acid is oxidised to form a radical. Why one seems to reduce
Copper (II) to Copper (I) Chloride in these conditions i do not know. At least it is a clue. |
Thanks Eldritch. Yeah, it's a real stumper. Do you have any resources/online links where the aldehyde connection is explained? The wikipedia
stoichiometry for the reduction of copper shows only that the net effect is the two hydrogens are lost (presumably to form water). How an aldehyde in
citric acid would cause the two hydrogens to be lost is a mystery to me. I would appreciate any links to clues.
[Edited on 25-1-2018 by semiconductive]
[Edited on 25-1-2018 by semiconductive]
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DraconicAcid
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| Quote: Originally posted by semiconductive | Is this why the drawing you showed me from wikipedia has hydroxide (OH) ions with no bonds being shown to any other nearby atom? They are making some
kind of hard distinction between ionic bond and covalent bond???
I've heard and seen chemistry where resonance effects are going on. In older texts, that was usually shown by a dotted line where a bond switched
from one atom to another. Indeeed, in the pictures of Citric acid one such bond is shown between the two OH radicals. The same type of bond is NOT
shown in the case of glucose.
But I have never seen someone draw an oxygen atom having three bonds ... like the picture you showed me from Wikipedia. And no, I've never heard of
the ion you asked me about.
|
I skip the quantum mechanical parts because, for my own sake, I'm sticking to the simpler models.
The hydroxide shown in the picture isn't shown as bonded to anything, I think, only because it's bonded to atoms that are outside of that particular
unit cell. They aren't making a hard distinction between ionic and covalent bonds- they show a bond whenever the two atoms are within a certain
distance.
A hydronium ion is the H3O+ ion that you get in aqueous solutions of acid. Any time you have a water molecule acting as a ligand to a metal, you will
also have an oxygen with three bonds.
Check out https://www.ccdc.cam.ac.uk/structures/?
A lot of the structures are too complex to be of interest to me, but if you search for "diaqua" and "copper" you can find some nice ones (and view
them as the unit cell, or a collection of unit cells. They don't have basic copper carbonate, though).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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semiconductive
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| Quote: Originally posted by DraconicAcid |
When he talks about ammonia, he does say this, but when he's talking about various chlorides (i.e., copper(II) chloride and mixed salts with cadmium
and other chlorides), he does dismiss the chlorides and speaks only of the number of water molecules. |
in the paper, he noted that anhydrous cupric chloride was "yellow-brown" (P1066); so naturally, he's going to talk about the change in color due to
the number of molecules added for hydration. I don't see how you come to the conclusion that he "dismisses" chlorine? The chlorine obviously
doesn't cause the bluish color, on it's own; it's the water molecules that shift the color to blue.
I didn't pay attention to the mixed salts, because I'm not working with them yet. It's information overload. But, if we know water is sufficient to
cause an ion to be a particular color ... and changing anions does not change the color, SO4, Cl, then why would he pay attention to the particular
anion? Wouldn't he be justified in assuming it plays a minor role and maybe shifts the color an imperceptable amount? With the anions in scope, the
water is the one who's bonding interaction (with some SO4,Cl, or other anion assumed) and the copper that causes the distinct effect?
Which statement, on what page, are you singling out? I'm missing something.
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semiconductive
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| Quote: Originally posted by DraconicAcid | | They aren't making a hard distinction between ionic and covalent bonds- they show a bond whenever the two atoms are within a certain distance.
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I see. I've always understood bond sticks to represent the sharing of electrons to fill the orbitals; eg: octet rule and so forth. So, it's very
foreign to me to see a stick where there should be a dotted line for resonance. It's been 25 years, but the only other representation I recall seeing
is one where dots were placed between atoms to represent the number of electrons shared ... lewis diagram, maybe? Sometimes we would x out one of the
dots to show it didn't come from the adjacent atom ... but it's been too long.
The wikipedia drawing was just very confusing to me. The diagram I drew was merely to show an accounting of one configuration whiere all the orbitals
were properly filled by shared electrons. It's not impossible for there to be resonances not shown in my diagrams; but at least the diagrams I showed
satisfy the electron sharing requirements. I don't see why they are intrinsically impossible.
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DraconicAcid
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| Quote: Originally posted by semiconductive | The wikipedia drawing was just very confusing to me. The diagram I drew was merely to show an accounting of one configuration whiere all the orbitals
were properly filled by shared electrons. It's not impossible for there to be resonances not shown in my diagrams; but at least the diagrams I showed
satisfy the electron sharing requirements. I don't see why they are intrinsically impossible.
|
Because you've drawn it as if it were a simple molecule with copper having two bonds. The bonds with copper are coordinate bonds rather than
classical covalent bonds. Cu isn't going to need two bonds to satisfy its valence- it's going to have a coordination number of four or six in most
compounds.
Look- when you have sodium chloride, you don't have distinct Na-Cl molecules, and if you draw it as Na-Cl, you'll be told that it's wrong. In solid
sodium chloride, you have a sodium ion surrounded by, and equally attracted to, six chloride anions. It's not bonded to any one chloride more than it
is the other five close to it.
Here's another image of the structure of basic copper(II) carbonate:
Each carbonate bridges four copper atoms; each hydroxide bridges two of them (ignore how the structure shows each carbonate having two single bonds
and one double bond to carbon- that's just the software requiring a full octet, even though the three C-O bonds are equivalent). Each copper is
square planar, so there are sheets stacked on top of each other.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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wg48
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| Quote: Originally posted by semiconductive |
I've purchased a 1000 line/mm diffraction grating and have been planning to build a spectrometer capable of visible and infrared measurements down to
10 micron. Unfortunately, plastic of diffraction gratings are not good to infrared wavelengths used in transmission mode; and to get it to work in
reflection mode, I need to silver the back side of the film. I tried talking with the local high school chem teacher who has his students build a
crude spectrometer for visible wavelengths using an LED, and although he's excited about the idea of a wide range spectrometer for low cost, he
doesn't have the time to help me (wife needs attention kind of problems...!). So, it won't be until one of my sons is in his Chemistry class next
year that I have an excuse to pursue an advanced spectrometer with him. But that's what is really needed to fine tune the experients being conducted
on color. Thermal agitation ought to change the colors of the ions slightly, not enough to be seen by the human eye or a simple camera, but something
that could be measured by a simple spectrometer. That would be an invaluble tool in figuring out what is really going on in aqueous chemistry.
Again, I appreciate the link. I learned a lot. 
[Edited on 24-1-2018 by semiconductive] |
If the problem of using the plastic grating at IR wave lengths in transmission mode is the absorption by the plastic, then silvering the rear will
mean the IR must pass through it twice so the absorption would be greater. Perhaps you could silver the front then copper or nickel plate it
sufficiently thick that it can be peeled from the grating.
I liked the note I posted because it discussed the colors of the various copper compounds while giving the chain of reasoning as to how the
conclusions was reached. A more practical approuch than many more theory orientated books.
Your were welcome, I am glad it helped you.
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semiconductive
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| Quote: Originally posted by wg48 |
If the problem of using the plastic grating at IR wave lengths in transmission mode is the absorption by the plastic, then silvering the rear will
mean the IR must pass through it twice so the absorption would be greater. Perhaps you could silver the front then copper or nickel plate it
sufficiently thick that it can be peeled from the grating.
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That's very logical; I haven't worked out all the math or even what angles IR will reflect at given a 1000 lines/mm, but I know some qualitative
information guiding my thoughts. Light has both wave and particle characteristics. A dielectric, like plastic, can transmit a wave for a certain
distance (less than one wavelength) before the wave-packet collapses and we can detect a change in the photon. The change is what allows us to know
whether/what part of the plastic it went through. (Think Young's double slit experiment, and the spaces between atoms in plastic being equivalent to
slits; while the atoms block photons.)
In essence, there are odd situations where only the wave character of the photon HAS penetrated the dielectric deeply enough to be reflected off a
different dielectric behind the front surface of the plastic.
A similar effect can be seen with a glass of water, where the light reflects off the back side of the glass and the photon doen't leave the glass and
come back inside; For if you look through the top of water to the glass at a certain angle you will see a 100% reflection mirror. But if you bring
your finger to the back side of the glass to change the dielectric interface ... all the sudden you can see where your finger touches the glass, but
you will still see reflection in the spaces between your skin cells unless they are within 1 wavelength of light.
Paper and plastic films are on the order of 0.001 inch thick or less. For longwave infrared that's on the order of 1.2 or less wavelengths. It's a
gamble, but if I put a conductor chemically in intimate contact with the plastic, it will modify the conductivity of nearby atoms by changing the
electric field they experience. There's a chance that a cheap plastic diffraction grating will be rendered useful in a very expensive application
arena, whereas if the light goes all the way THROUGH the plastic, light scattering is certain and problematic.
Diffraction grating mirrors found on ebay are expensive, and those from scientific houses more expensive. The only choices (besides your suggestion)
that I see within an amateur's budget are to sensitize a silver or copper plated surface with a photochemical ( It Can't be silven nitrate, because it
makes granular crystals that aren't small enough. ) and then use a laser pointer to make the image of a diffraction grating using another diffraction
grating. The second possibility, is luck -- and a very thin plastic grating. The one I bought from ThunderOptics (TM) cost $4, but it came all the
way from France; so replacing it would take a lot of time if I screw up. I can't measure the thickness without damaging the rulings so I don't know
the odds of success. But, the plastic is so thin that even the stress of the paper mounting causes visible ripples in it. It's a real gamble, but
at least it's something I'm confident I can do.
Silvering or coppering the front would be delightful. In fact, since were working on copper in this thread it would be exciting to learn how to
precipitate copper metal just like silver. (Copper and silver are both better IR reflectors than nickel.) That's something I would love to know how
to do with home lab equipment. What is needed?
If you know a source of cheaper reflective diffraction gratings ... I'm all ears! Reflection gratings can be made very sensitive and precise (such
as the Paschensen series photographed by a Paschen mounted grating ) without suffering from extra complications due to noticable refraction,
nonlinear/predictable dispersion and absorption effects that all dielectrics cause in transmission mode.
Second picture of Paschen design from "Modern College Physics", by Harvey E. White (C) 1966. Fair Use intended only for personal research and
discussion.
 
[Edited on 26-1-2018 by semiconductive]
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semiconductive
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Now that I'm looking:
http://optics.sgu.ru/~ulianov/Students/Books/Applied_Optics/...
| Quote: | | Lindau has developed simple theoretical models for the groove profile generated by making master gratings holographically, and shown that
even the application of a thin metallic coating to the holographically produced groove profile can alter that profile |
How annoying ! Nothng's ever simple. 
Just for reference:
A typical $30 (amateur cost range) nano-engraved grating is labeled as "PET" so, I assume that it's cheap because PET plastic is used;
https://www.ebay.com/itm/36x38mm-Ultra-Precision-Nano-Engrav...
However, when I look up PET plasic transmission characteristics it's clearly 0 (at least once) before reaching even 2 microns of wavelength. So the
usefulness of even semi-expensive gratings at 10 microns of IR (the bond energy of many molecules and things in water) will be nil.
https://www.hitachi-hightech.com/products/images/8414/uh4150...
I might be able to get away with less lines/mm because IR wavelengths are much longer compared to visible light; but I don't see anything useful or
unconventional available. Even CDRoms at 600 lines/inch have unintended diffraction grating on the back side of a thick plastic layer. Dissolving
off the plastic without ruining the grating is probably nearly impossible.
For whatever reason, when I see picturs of fine mesh wire filters, those don't seem irridesecent like a cdrom though the spacing is similar to tracks
on a CD.
EDIT: (CD tracks are 1 micron apart according to some sources, so maybe I was mistaken earlier.)
I'm not sure a stainless steel mesh would even work. That's the only other kind of thing I can think of that would act like a diffraction grating.
The only other kind of technique I can think of is trying to form some kind of thin film; like clear nail polish on paper; But I'mm uncertain if it
can detect all colors by changing the angle, or not ... or if it's wavelength specific to thickness, alone.
https://www.kiwico.com/diy/Science-Projects-for-Kids/3/proje...
[Edited on 26-1-2018 by semiconductive]
[Edited on 26-1-2018 by semiconductive]
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