What solids other than water float on their liquid forms?

February 20, 2007 12:49 PM

Are there any substances, other than water, where the solid form is less dense than the liquid?

Does hydrogen bonding take place in other substances during the transition from liquid to solid?

posted by Baby_Balrog to Religion & Philosophy (18 answers total)

I am intently interested in how this is a religion and philosophy question. I think there is a background we are missing. Apparently gallium and bismuth are candidates.
posted by MeetMegan at 12:57 PM on February 20, 2007

Response by poster: I'm writing a fascinating book.

hi megan. :D
posted by Baby_Balrog at 12:58 PM on February 20, 2007

Best answer: However, this Duke University lesson plan says "Water is the only natural substance for which the solid form is less dense than the liquid form."
posted by MeetMegan at 12:58 PM on February 20, 2007

Gallium, bismuth, acetic acid, antimony and silicon.
posted by bshort at 12:59 PM on February 20, 2007

Aerogels? Though I suspect that polymers aren't quite what you were after.
posted by TheNewWazoo at 12:59 PM on February 20, 2007

I'm fascinated by this book you are writing.

Hi B_B. When are we going to get together?
posted by MeetMegan at 1:00 PM on February 20, 2007

(from here)
posted by bshort at 1:00 PM on February 20, 2007

Response by poster: Maybe I should amend my question. Are there any naturally occuring substances which meet these specifications?
posted by Baby_Balrog at 1:02 PM on February 20, 2007

Response by poster: gah... should have previewed. I'm co-authoring a book with another of my div-school peers. It involves interviews with angels involved in the genesis. Someone fudges the design for water in order to accomodate the existence of life and is cast into the outer darkness. It's all quite humerous, I assure you.

soon? :) i'll call u.
posted by Baby_Balrog at 1:05 PM on February 20, 2007

bshort, I don't believe acetic acid is correct, in spite of the Wikipedia article. (Wikipedia's own acetic acid article cites a higher density for the solid than for the liquid.)

As to BB's second question, "Does hydrogen bonding take place in other substances during the transition from liquid to solid?" Sure. Just about any substance capable of forming hydrogen bonds will do so upon freezing. It's not the hydrogen bonding in and of itself that causes ice to be less dense than liquid water. It's that for water, the hydrogen bonding forces the molecules into a crystal structure with lots of empty space. Lots of compounds have hydrogen bonding involved in their crystal structure, but for most of them, that doesn't force them into a weird configuration with lots of empty space.
posted by DevilsAdvocate at 1:27 PM on February 20, 2007

Best answer: Oh, and if you're trying to Google, another way of expressing the same thing is that the solid-liquid boundary line (also called the melting curve or the fusion curve) on a temperature-pressure phase diagram has negative slope. Playing around with those terms might get you somewhere. I didn't do so hot with trying to find more substances using those terms, as you get a lot of pages noting that the curve has a negative slope on water's phase diagram, and there's other boundaries on phase diagrams (especially for substances with multiple solid phases) which can have negative slope, but if you're trying to confirm a particular substance, you can throw that substance in with your other search terms.
posted by DevilsAdvocate at 1:40 PM on February 20, 2007 [1 favorite]

You can also google on negative coefficient of thermal expansion. That won't get you cases where there is a large volume expansion during freezing/crystallization, but it will get you to the likely candidates.

Bismuth is the most dramatic example I know of, besides water ice. I'm skeptical about the acetic acid that's been cited above. Anecdotally, in a bottle of glacial acetic acid the crystals and frozen sludge are at the top of the liquid, but I always assumed that was related to evaporation at the inferace rather than a simple density difference.
posted by janell at 2:39 PM on February 20, 2007

I can tell you firsthand that gallium is definitely denser as a liquid than as a solid. Whether gallium is "naturally-occuring" is questionable, at least as a pure material.
posted by JMOZ at 5:06 PM on February 20, 2007

I think only ice has the property. And Ice-Nine of course.
posted by AmbroseChapel at 6:25 PM on February 20, 2007

Response by poster: Thank you all! Everyone who answered gets a free copy of the book. I love this website.
posted by Baby_Balrog at 9:13 PM on February 20, 2007

Can I get one too? ;)
posted by Clementines4ever at 10:38 PM on February 20, 2007

Plutonium!
posted by nervestaple at 11:16 PM on February 20, 2007

I'm pretty sure some organic compounds do. I've worked with some plasticizers that had really high freezing points (as in they would freeze in a cool room) and I think the ice floated. Can't remember the particular formulas off the top of my head, though.
posted by Kadin2048 at 12:49 AM on February 21, 2007