Sciencemadness Discussion Board

Metals in their gaseous states?

bolbol - 12-1-2017 at 20:54

I was wondering about the nature of metals in their gaseous forms. When you heat a transition metal past its boiling point, do you get a gaseous molecules of that metal or do they ionize and form plasma? What would be the color of these gasses?

DraconicAcid - 12-1-2017 at 21:04

I don't know about transition metals, but I believe the alkali metals form diatomic gas molecules which are coloured. Alkaline earths are monoatomic.

j_sum1 - 12-1-2017 at 23:04

Mercury is monatomic in the gas phase but this (old) paper suggests a less stable diatomic state.
https://www.jstor.org/stable/96492?seq=1#page_scan_tab_conte...

Alkali metals are believed to be stable in the gas phase as diatomic molecules.
http://chemistry.stackexchange.com/questions/32686/is-it-pos...

Group VI metals -- Cr, Mo and W, and also U are believed to form diatomic molecules with a sextuple bond.
https://en.wikipedia.org/wiki/Sextuple_bond

Silicon can be diatomic in the gas phase
http://pubs.acs.org/doi/abs/10.1021/cen-v086n034.p010
As can carbon.

Vaporised metals can also exhibit aromicity.
https://en.wikipedia.org/wiki/Metal_aromaticity


[Edit]
This seems to be the sort of thing that blogfast would know a bit about. Missing him at the moment.
woelen probably has some clues as well.

[Edited on 13-1-2017 by j_sum1]

chornedsnorkack - 15-1-2017 at 07:27

For example, what happens when a current carrying tungsten wire breaks? In the normal operation, the filament is below its melting point. But as the filament cross-section narrows at some point, the resistance in that point grows, the voltage drop concentrates there, and the power production rises there, increasing the temperature. Should the tungsten wire be heated to boiling? And when tungsten does boil, how well does the tungsten vapour conduct electricity compared to the neighbouring molten tungsten?
What is the colour of tungsten vapour produced by boiling of a tungsten filament?

phlogiston - 15-1-2017 at 15:13

In high school we had to derive the melting point of tungsten experimentally in that way.
You monitor the voltage/current through a small lamp until it breaks. The resistance of the wire depends on the temperature and you can work approximately at what temperature the wire broke (presumably by melting rather than boiling).

TheMrbunGee - 16-1-2017 at 01:07

Potassium gas is blue, but it really would be interesting to find out what does tungsten or any other metal smell like. I wonder if it would be similar to something or completely new odor.

j_sum1 - 16-1-2017 at 01:53

I thought K gas was greenish. It appears so in videos I have seen.

I would not want to smell something as hot as gaseous tungsten.

chornedsnorkack - 16-1-2017 at 12:46

Problem with it is that the only metal that has appreciable vapour pressure at room temperature is quicksilver. It is known not to have smell.
One metal that does smell is osmium. But that´s the smell of osmium oxide.

In a breathable environment, i. e. cold air, hot tungsten vapour would rapidly oxidize to tungsten trioxide, which might then condense into dust/smoke.
When hot tungsten is exposed to air by breaking a burning bulb, does burning of the filament create tungsten trioxide smoke in visible and smellable amounts?

wg48 - 16-1-2017 at 16:03

There was a smell from this glowing and smoking tungsten rod but it may have been the zinc from the zinc plated bolts and washers combined with volatiles from the wiring and transformer, as they got hot. The smell was not unusual to me.

I have previously noticed a distinct smell in a vacuum chamber when it was first opened to air after evaporating tungsten. But that may have been a similar effect to that which produces the smell from copper after its handled by a bare hand. Clean copper has no smell.

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woelen - 17-1-2017 at 03:40

You cannot smell hot gaseous metals. As soon as these metal gases are exposed to cold air, they condense to fine dust and many metals also will be oxidized. So, if you smell anything, it will be very fine metal smoke or metal oxide smoke.

The appearance of metal gases which boil at very high temperatures (2000K or even hotter) will be the same for most metals. They will look like a very hot opaque light emitting cloud. Any color of their own will be masked by the intense glow. It is like the sun. The sun's gases/plasmas have no own color, the high temperature of the gases makes them glow.

j_sum1 - 17-1-2017 at 04:05

Do you know anything more about their molecular structure -- which ones exist as monatomic and which ones are diatomic -- and whether any other forms are possible?

chornedsnorkack - 17-1-2017 at 06:35

Quote: Originally posted by woelen  
The appearance of metal gases which boil at very high temperatures (2000K or even hotter) will be the same for most metals. They will look like a very hot opaque light emitting cloud. Any color of their own will be masked by the intense glow. It is like the sun. The sun's gases/plasmas have no own color, the high temperature of the gases makes them glow.


Only if they are black bodies. Yet the chromosphere of Sun is red.
Likewise, a bunch of low boiling metals emit their individual spectral lines rather than black body spectra, and give distinctive colour to flames.
Which metals have different and recognizable colours when evaporated by being welded above 1700 Celsius?

[Edited on 17-1-2017 by chornedsnorkack]

wg48 - 17-1-2017 at 06:53

Quote: Originally posted by woelen  
You cannot smell hot gaseous metals. As soon as these metal gases are exposed to cold air, they condense to fine dust and many metals also will be oxidized. So, if you smell anything, it will be very fine metal smoke or metal oxide smoke.

The appearance of metal gases which boil at very high temperatures (2000K or even hotter) will be the same for most metals. They will look like a very hot opaque light emitting cloud. Any color of their own will be masked by the intense glow. It is like the sun. The sun's gases/plasmas have no own color, the high temperature of the gases makes them glow.


Yes I doubt very much that its gaseous tungsten, gaseous zinc or solid copper that directly produces a smell. Its same with apple pie, toast or dog poo LOL Unlike say hydrogen sulphide or naphthalene.

Gaseous metals do have colours caused emission and absorption of the limited energy levels of their electrons.

Hot solid metals are different. The energy levels of the outer electrons of the atoms of the solid merge to produce a near continuum (conduction band) and are responsible for the near perfect blackbody radiation from them.





[Edited on 17-1-2017 by wg48]

phlogiston - 17-1-2017 at 09:07

The color of sparks between two metal electrodes are noticeable different depending on the metal, which I assume would be an indication of the color of the light emitted by the metal vapor.

Two copper wires yield green sparks
Steel typically gives yellowish white, branching sparks (color and amount of branching depending mainly on the carbon content, so probably a lot of black body radiation).

Lead gives white-blueish.

etc.etc.

I've never tried alkali metals, but might be fun to do as some of them should provide distinct colors. potassium should produce green, lithium red, cesium blue, etc.

woelen - 18-1-2017 at 01:38

What I meant with my remark about colors of gaseous metals is that you will not observe a colored gas like Cl2, NO2, I2-vapor etc. For the low-boiling metals there may be color (e.g. potassium, sodium), but the metals which are gaseous at very high temperature emit light of their own, which will overwhelm any color the vapor might have. The emitted light indeed can have a certain color, specific for the metal, but I do not consider this as the color of the gaseous light.

Look at it like the color of a LED. Many modern LEDs simply are glass-like things with metallic-looking electrodes, which have a grey or silvery blob in the glass. When you switch on the LED it emits light of a specific color (e.g. blue, green, yellow, or even white, which is a mix of colors). What is meant with "the color of the LED"? The LED itself only is a glassy/transparent object with some silvery little spot in it. The emitted light has a certain color. This is the analogy I see with hot gaseous metals. The main difference is that the extremely hot metal gas does not have a state in which it does not emit light, so speaking of the color of the metal gas itself is fairly meaningless (except, as stated before,for some low-boiling metals, which can be gaseous at temperatures where there is not a very bright light emission).

morsagh - 19-1-2017 at 11:37

What about metals which are aromatic in gaseous phase, so there should be some UV-VIS absorbtion, so color too?

fluorescence - 20-1-2017 at 14:22

On the first few comments, are you sure all Alkli Metals form dimers in their gas phase ?

I was filming the reaction of potassium in H3PO4 a while ago and saw that shortly before and after the metal catches fire it is suddenly surrounded by a cloud of green gas. As I knew about the color of gaseous Alkli metals I checked for it in the Gmelin, a very old sample we had in our university's library and they mentioned there that at its boiling point potassium will not form that many dimers much in comparison with sodium I think. The results might be a bit out of date so if there are newer tests on the actual composition of potassiums gas phase I'd be interested in it.