The Elements of the Periodic Table

[don willard]

Can each of the basic elements exist in all three energy state forms? For instance I know there is liquid helium, but is there solid helium? What about solid hydrogen, would it be a metal? Can mercury be a solid at some temperature, or can silocon be a gas, etc.? What about neptunium gas? I heard that some elements sublimate or go right from solid to gas and have no liquid state in between.
Is this right?

[mnemosyne]

All of the elements can exist in all three forms - the thing is, most are never exposed to the necessary conditions. Helium, for example, is a gas because it only solidifies at -272 C and becomes gaseous at -268.94 (meaning it's only a liquid for a span of about 3 degrees, right near abslolute zero). Hydrogen would never be a metal since it doesn't have the right properties, but it exists as a solid at -259.2 C. Silicon is a liquid at 1410 C, and gas at 2355 C. Mercury is solid at -38.9 C and gaseous at 356.5. I couldn't quickly find the melting and boiling points of neptunium, though a little research should find it. For an easy reference for most of the important basic properties of elements and compunds, try http://www.chemfinder.com , and if they dont have it, follow the given links.

I don't have much info on sublimation offhand, either, but to my knowledge all compunds are capable of doing so, but some are just more prone to it since they are more often exposed to the right conditions. Water, for example, sublimates to make snow, but in other conditions it goes through the normal phases (warm up ice, you get water, then vapour).

[mnemosyne]

Ok, I was wrong about the hydrogen - it can have metallic properties under certain conditions.

from http://www-phys.llnl.gov/H_Div/GG/ComQuest.html:


What do you mean by a metal?
Metallic fluid hydrogen is achieved when high pressures reduce the energy gap Eg between the filled valence-electron band and the unfilled conduction-electron band down to Eg~kBT, where kB is Boltzmann's constant and T is the temperature. When Eg~kBT, thermal smearing in the disordered fluid fills in the energy gap, a metallic density of electronic states is achieved, and the electronic system has a Fermi surface characteristic of a metal.


I'm not going to look into it any more than that - just do a google search on hygrogen metallic properties (or some such keywords) and find out all you want to know.

[Squink]

Silicon boils at 2355 c.
Neptunium boils at 3902 c.
Osmium is the hardest to vaporise with a B.P. of ~5000 degrees centigrade.

[Threadkiller]

Originally posted by mnemosyne
...
Water, for example, sublimates to make snow, but in other conditions it goes through the normal phases (warm up ice, you get water, then vapour)
...

Websters Ninth Collegiate Dictionary:
Sublime:
To cause to pass directly from the solid to the vapor state

The common form of sublimation (for most of us) is the phase change from dry ice to carbon dioxide vapor. Atmospheric pressure is too low to get liquid carbon dioxide.

[CC]

Water doesn't sublime to MAKE snow - it sublimes FROM snow (solid) into vapor. To illustrate this to yourself, notice how piles of snow get smaller and smaller, even when the temperature has not gone above the melting point. The snow is subliming - turning directly into a gas. Iodine has a melting point listed in the handbook of physics and chemistry, but really doesn't exist as a liquid - it, too, sublimes directly to a beautiful purple gas. (poisonous, too). In that same source, Neptunium's b.p. is estimated to be 3902 C. This indicates that it, too, can become a gas. Mercury, by the way, freezes at about 40 below zero (which is the same Fahrenheit as Celsius) and can fairly easily be made into a solid in the lab/classroom, by using dry ice.

[mnemosyne]

Originally posted by CC
Water doesn't sublime to MAKE snow - it sublimes FROM snow (solid) into vapor.

I should have known that - silly me. But is has been several years since general chem for me. All I deal with now is organic!

[AWB]

Originally posted by Squink
Silicon boils at 2355 c.
Neptunium boils at 3902 c.
Osmium is the hardest to vaporise with a B.P. of ~5000 degrees centigrade.

Au contraire! Tungsten has a boiling point of 5660oC.

[Phobos]

Originally posted by mnemosyne
...hydrogen - it can have metallic properties under certain conditions.


FWIW, metallic hydrogen exists inside Jupiter.

from The Nine Planets - Jupiter (http://www.seds.org/billa/tnp/jupiter.html)
Above the core lies the main bulk of the planet in the form of liquid metallic hydrogen. This exotic form of the most common of elements is possible only at pressures exceeding 4 million bars, as is the case in the interior of Jupiter (and Saturn). Liquid metallic hydrogen consists of ionized protons and electrons (like the interior of the Sun but at a far lower temperature). At the temperature and pressure of Jupiter's interior hydrogen is a liquid, not a gas. It is an electrical conductor and the source of Jupiter's magnetic field. This layer probably also contains some helium and traces of various "ices".


The outer planets/moons also have things like nitrogen snows etc.

[Yossarian]

http://www.webelements.com

[Johanna]

So what about carbon? Can you melt carbon? Huh?

[tracer]

Mmmmm, molten charcoal....

[Squink]

Au contraire! Tungsten has a boiling point of 5660°C.

Oops, Rhenium is over 5600° as well ! It's a good thing there isn't a pit of bubbling Tungsten around here or my embarassment would surely cause me to cast myself in.

Carbon becomes a gas at ~4827° C. In the presence of Oxygen, it will burn at a much lower temperature and be converted to carbon dioxide gas.

[don willard]

I knew hydrogen had to be metallic as a solid and as a liquid because it is right above lithium and the other reactive metals on the Periodic Table of the Elements.
(What do you call a flickering picture of pachyderms? Ans:
A Periodic Tableau of the Elephants.
Now several wrote of sublimation. Snow sublimates to gas but it can also melt to liquid. Carbon, someone said, turns to a gas, but what conditions could make it liquid?

[iampunha]

don willard, adequate pressure might make it possible to turn carbon from solid into liquid.

[Squink]

If you heat carbon in an inert atmosphere, e.g. Argon, it will melt at ~3550° C.