[Seany (OP)]

Just a question.. What is the lightest gas?

[another_someone]

The question is of itself ambiguous.

The lightest atom is the hydrogen atom, and the lightest ordinary molecule is the hydrogen molecule (composed of two hydrogen atoms, but still lighter than a helium atom, because ordinary hydrogen does not have the neutrons of a helium atom).

To talk about the lightest gas, one has to take into account the pressure and temperature at which the gas is at.  An ultra low pressure nitrogen gas can be lighter than a high pressure hydrogen gas, and given the lower boiling point of helium, at low temperatures, hydrogen can condense into a liquid that is heavier than helium which will remain a gas for very much lower temperatures.

A clear example of this difficulty is when dealing with water.  Water, as steam, is lighter than air (at the same pressure and temperature), but as a liquid (at the same pressure and temperature as the air) will be heavier than air.

At the temperature and pressure of liquid water, then hydrogen would be the lightest of the gasses.

[DoctorBeaver]

I bet Seany didn't expect an answer like that!  []

[Seany (OP)]

Err nope.. LOL thanks George..

How about at ground level, room temperature... ?

[chris]

Hydrogen

[Seany (OP)]

Thanks []

[Bored chemist]

The free electrons in a metal or other conductor act like a gas and the electrons are roughly 2000 times lighter than hydrogen atoms.

[another_someone]

The free electrons in a metal or other conductor act like a gas and the electrons are roughly 2000 times lighter than hydrogen atoms.

Since, as far as I am aware, the electrons do not obey Boyles law, I would think that the argument that they act 'like a gas' to be somewhat limited in context.

[Bored chemist]

Only "ideal" gases obey Boyle's law. No real gas is ideal. The extent to which anything can be said to act like a gas is limited.
If the electrons in a metal acted in all regards like a gas then I would have said that they were a gas rather than that they acted like one.

[lightarrow]

The free electrons in a metal or other conductor act like a gas and the electrons are roughly 2000 times lighter than hydrogen atoms.

If you want to consider that as a gas, then you could do the same with photons in a radiating cavity. In this case, EM radiation should be lighter than electrons! []
(It depends on cavity's energy however).