[shelley]

Hi,
Which element from the periodic table has a yellow-green gas under STP? 
What are the keywords I can type into Google to locate information about chemical molecule names?  I want to learn to differentiate between a solid or liquid molecule by reading its name.
Thank you.

[discodermolide]

Well you could just type in the molecule's name and add solid or liquid.
You could check the ChemSpider database at http://www.chemspider.com.
I just copied and pasted your original question and it gave me fluorine as the answer, as well as this question in these fora.

[curiouscat]

Couldn't this be Chlorine too?

[discodermolide]

Of course, the second or third answer said fluorine.

[Arkcon]

I really don't see how you can be absolutely sure of the phase a molecule will have based only on its name.  You can almost be sure a large molecule won't be a gas, but ... how large is large?

[curiouscat]

I really don't see how you can be absolutely sure of the phase a molecule will have based only on its name.  You can almost be sure a large molecule won't be a gas, but ... how large is large?

Funny, I'd just asked almost this exact question a few weeks ago on here:

http://www.chemicalforums.com/index.php?topic=61474.msg219470#msg219470

Apparantly WF6 wins; so above a MW of 297 you can be sure it is a liquid.  But that's  a very conservative assumption.

As an aside I wonder what's the largest MW hydrocarbon (ok, let's stretch definitions to allow C H O ) that's still a gas (BP <20 C at 1 atm. ). That should prevent sneaky metal atoms from bumping the weight up. We should get a more realistic Gas-Liquid transition MW using this.

Allowing S and N might boost up the MW a bit but not as much as the metal flurides.