And the answer is:
1. I am the reason water can be liquid at room temperature
2. I am the reason water ice floats on liquid water
What am I?
Hydrogen bonding!
Many folks got it right. Good job.
Answers of forces bet ween molecules is also correct, although not as specific as I was looking for.
Clue 1.
In a rough way, molecules that cannot hydrogen bond have a vapor pressure that relates to their physical size. Larger molecules have more interactions between each other than do smaller ones, and thus the smaller ones are more likely to turn to gas than liquid or solid.
Molecules of similar size to water and that cannot hydrogen bond, such as methane (CH4), hydrogen sulfide (H2S). phosphine (PH3), borane (BH3), silane (SiH4) and hydrogen chloride (HCl) are all gases at room temperature.
Why is water different? It is because liquid and solid phase water molecules interact with one another by hydrogen bonding. That bonding is much stronger than the ways that other molecules interact, with van der walls and dipole interactions.
A hydrogen bond can only exist for any reasonable period of time in liquid or solid water, not in the gas phase. That effect then stabilizes water in those two phases relative to the gas phase, and makes liquid water possible at room temperature.
Here's a drawing that shows hydrogen bonds (the dashed lines) in liquid water:
Cohesion: Hydrogen Bonds Make Water StickyWater has an amazing ability to adhere (stick) to itself and to other substances. The property of cohesion describes the ability of water molecules to be attracted to other water molecules, which allows water to be a "sticky" liquid.Hydrogen bonds are...
www.usgs.gov
Clue 2.
It is a curiosity that the hydrogen bonds in ice actually make the density of solid water ice to be less than that in liquid water. Thus ice floats. In part, that is because there are more hydrogen bonds in ice (4 per water molecule) than in liquid water (average 3.4 per water molecule). Still, one might expect that more bonding would pull the water molecules closer together and increase the density. But the bonding is very angle/orientation specific, and the pickup of additional hydrogen bonding in ice comes at the price of pushing the water molecules further apart to precisely fit the optimal orientations for hydrogen binding.
This easy to read articles discusses that effect a bit:
Thanks everyone for playing and Happy Reefing!
www.reef2reef.com
