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Author: Subject: The weirdest chemical element ?
metalresearcher
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[*] posted on 29-9-2014 at 09:31
The weirdest chemical element ?


Of all nonvirtual elements (i.e. which do exist in nature, even at very small quantities such as At or Fr, or have known p[hysical and chemical properties), which element has the weirdest properties ?

I'll kick off with number 6, the C.

- the only element never prepared in its liquid state: it has no melting point an any (?) pressure
- insoluble in most substances (although B has the same ?)
- largest amount of compounds (organic chemistry)
- several solod crystal states, not only diamond and graphite
- the hardest elemental mineral

What are your ideas ?
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Brain&Force
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[*] posted on 29-9-2014 at 10:33


Lithium can be just weird, as are pretty much all of the lanthanides.




Raney nickel can't hydrogenate dank memes.
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Amos
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[*] posted on 29-9-2014 at 10:48


Carbon is pretty unique, that should go without saying(buckyballs!). Also selenium is really weird, especially regarding its allotropes.



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bismuthate
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[*] posted on 29-9-2014 at 10:51


Possibly sulfur because you could extensively study sulfur's chemistry with only itself due to its many allotropes.
Antimony is also really odd because it can be explosive and is kind of a metal and kind of not. So is polonium.

[Edited on 29-9-2014 by bismuthate]




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[*] posted on 29-9-2014 at 12:07


Platinum is interesting because it catalyzes so many reactions, while being refractory itself.

Fluorine is exceptional because it forms compounds with almost all other elements except Helium and Neon. That's pretty hard to topple, I think. Of course, Fluorine combines also with the abovementioned Mr. Platinum & Co.
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Dan Vizine
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[*] posted on 29-9-2014 at 14:18


Helium is the most unusual, hands down.

For various forms....

Superfluidity, boiling without bubbles, heat conductivity of an astounding degree, a quantum world you can watch!. If you want really unusual behavior, this gas is the champ.

Bose-Einstein condensates of Rb are good runners-up.




[Edited on 29-9-2014 by Dan Vizine]
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[*] posted on 29-9-2014 at 21:43


Xenon, because of all of its weird chemistry.
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blogfast25
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[*] posted on 30-9-2014 at 06:49


Helium of course.



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Pok
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[*] posted on 30-9-2014 at 08:06


Quote: Originally posted by bismuthate  
Antimony is also really odd because it can be explosive

This is only a myth. There is not such an allotrope of antimony that is explosive. It's something like a compound with chlorine, but not pure antimony.

Thallium is quite weird. It doesn't know whether it's an alkali metal or a heavy metal.
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Zyklon-A
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[*] posted on 30-9-2014 at 08:19


Pok, you sure?
My sources say it's an unstable allotrope of antimony, which contains Antimony trichloride in it's crystalline structure due to the way it's commonly prepared: by the slow electrolysis of a concentrated solution of antimony trichloride in hydrochloric acid.
http://lateralscience.blogspot.com/2012/07/explosive-antimon...




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[*] posted on 30-9-2014 at 08:42


Your sources are quite old (1934 and 1946). Although this myth can still be found in modern literature.

But look here: "The so-called explosive antimony is an ill-defined material always containing an appreciable amount of halogen; therefore, it no longer warrants consideration as a separate allotrope." (2014)

That's a very logical argument. An allotrope is an element in it's pure state. If no pure "explosive antimony" can be prepared, you can't claim that it is an allotrope. The claim of "allotrope" has never been confirmed. It always was only an assumption.
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[*] posted on 30-9-2014 at 09:40


Phosphorus!

Black, red, violet, two types of white, di- and mono-atomic gas phases, nanotubes and rods... all allotropes of the same element.




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[*] posted on 30-9-2014 at 14:32


Quote: Originally posted by Praxichys  
Phosphorus!

Black, red, violet, two types of white, di- and mono-atomic gas phases, nanotubes and rods... all allotropes of the same element.


And a black van with a SWAT team will pull up to your driveway if you try to buy it!

[Edited on 30-9-2014 by Cou]
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[*] posted on 30-9-2014 at 14:43
Plutonium is in the Running


Although handicapped because no one here can own or touch any plutonium, it has very strange properties - seven allotropes, including one where it shrinks with increasing temperature, has dramatic density changes with some phase changes (20%), and an extremely large coefficient of thermal expansion (depending on phase). It has a large density increase on melting, to become the element with the highest viscosity in its liquid phase.

It has the second-to-the-lowest electrical conductivity among the metals (only manganese is slightly lower), and the lowest thermal conductivity of any metal.

It has many other atypical properties: how other properties change with temperature (resistivity, magnetic susceptibility, etc.), unusually low melting point, etc.

(And if you have a chunk of this you will really have the government's interest!)

[Edited on 30-9-2014 by careysub]
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[*] posted on 1-10-2014 at 00:28


So many choices . . .

Let's see. Neon - the most unreactive element. Astatine - doesn't know whether it wants to be a halogen or a metal (shame it's ridiculously radioactive, though). Gold - a metal that's as electronegative as carbon and as a result is fairly good at forming anions, unusual for a metal.




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[*] posted on 1-10-2014 at 05:26


Iodine!

It's sublime.
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bismuthate
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[*] posted on 1-10-2014 at 09:09


So is arsenic.



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Dan Vizine
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[*] posted on 1-10-2014 at 11:23


If you define weird as having unique, surprising behavior then allotropy is hardly unique, a lot of elements have them. Some just have more than others.

The same can even be said of the complex allotropes. Nanotubes and graphene-like structures are not the sole provenance of carbon.

Electronegativities, reactivities, metal-non-metal ambivalence, ability to catenate are still just numbers on a continuous scale.

But helium---
1) has a negative Joule-Thomsom coefficient, the gas warms upon free release although if it starts at a low enough temperature it cools upon free expansion. Not unique, but this is just gravy.

2) Doesn't form compounds except quasi-stable species in a spark discharge. It and Neon remain "nobel". That's more unusual than argon, krypton and zenon having chemistry. After all, that was predicted.

3) Doesn't have a triple point. Not unique but unusual.

4) The density of liquid helium is only 25% of that expected from classical physics (it's getting weirder...). You could also say the atomic volume is 4 times the expected.

5) If you cool LHe to a little over 2 K, you get a different form of helium. LHe at 4 K is called helium I, at 2 K it is helium II. Helium I contracts with decreasing temp, then expands upon becoming helium II. Later, it shrinks again if you get colder still.

6) Helium II shows superfluidity. Place an empty cup in LHe II and helium creeps up the wall and then into the beaker until the levels equalize inside the cup and outside.

7) Helium II has a thermal conductivity several hundred times higher than copper or silver. It can't boil with bubbles. No temperature differences are tolerated. It turns to gas with no boiling. Heat transfer through LHe II is ~20 meters per second. The heat transfer is quatum mechanical in nature and is termed "second sound" because it is so fast.

8) LHe I has a viscosity of ~ 25 cp. Water has a viscosity of 10,000 cp at 20 C. But LHe II has a viscosity of less than 0.00001 cp. It moves in a "Rollin" film and for the longest time physicists couldn't even measure its viscosity.

9) He-4 and He-3 both exist. When you liquify a 50-50 mixture, it separates into two immiscible liquids.

Many of the characteristics of helium can be seen as nothing else than quantum effects writ big! Just as quantum chemistry/physics is shocking and confusing to most people, I'm afraid no other element can touch helium as the most unusual element for exactly that reason.


[Edited on 2-10-2014 by Dan Vizine]
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[*] posted on 1-10-2014 at 11:34


Quote: Originally posted by Dan Vizine  
9) He-4 and He-3 both exist. When you liquify a 50-50 mixture, it separates into two immiscible liqiuds.



Now that is truly interesting!




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[*] posted on 1-10-2014 at 11:44


Quote: Originally posted by blogfast25  
Quote: Originally posted by Dan Vizine  
9) He-4 and He-3 both exist. When you liquify a 50-50 mixture, it separates into two immiscible liqiuds.



Now that is truly interesting!


Apparently that one neutron makes all the difference. The two follow different quantum statistics. He-3 doesn't even show a transition to superfluidity. An entirely different animal.
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[*] posted on 1-10-2014 at 15:19


Dan makes a good case, I'm voting for helium!
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[*] posted on 2-10-2014 at 07:22


Quote: Originally posted by Dan Vizine  
Quote: Originally posted by blogfast25  
Quote: Originally posted by Dan Vizine  
9) He-4 and He-3 both exist. When you liquify a 50-50 mixture, it separates into two immiscible liqiuds.



Now that is truly interesting!


Apparently that one neutron makes all the difference. The two follow different quantum statistics. He-3 doesn't even show a transition to superfluidity. An entirely different animal.


Probably to do with the fact that one is a boson while the other is a fermion.
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[*] posted on 2-10-2014 at 08:47


I thought He-3 was superfluid but at a lower temperature by pairing. Though superfluidity and Bose-Einstein condensates are states of matter.

[Edited on 2-10-2014 by Marvin]
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Dan Vizine
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[*] posted on 2-10-2014 at 09:50


Quote: Originally posted by Marvin  
I thought He-3 was superfluid but at a lower temperature by pairing. Though superfluidity and Bose-Einstein condensates are states of matter.

[Edited on 2-10-2014 by Marvin]


Hi Marvin,

You undoubtedly have more recent information than my dated source material. It said " A recent calculation, however, shows that between 0.008 and 0.00002 K it [LHe-3] should exhibit this phenomenon [superfluidity]"

One experimenter reported a slight rise in heat capacity of LHe-3 at 0.0055 K and suggested that this was indicative of a superfluid phase change. The claim was unresolved at the time.
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[*] posted on 2-10-2014 at 12:03


I'm not sure my information is newer, it was a tertiary ref I think and I can't remember which. It struck a chord because it was two fermions (asymmetric wavefunctions) pairing to create a boson (symmetric wavefunction) which can then condense, mirroring the cooper pair mechanism in superconductivity.
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