Density

[MrsDunnLewis]

what are the two substances that are less dense when in a solid (frozen) state than they are in a liquid state?

[OBonio]

Water is one (ice floats).

[ll_billym]

Gallium.

[Gef]

Water is correct and it is caused by the hydrogen bonds which cause the water molecules to move apart as it freezes. This might also be possible in other substances which exhibit hydrogen bonding such as HF. I can see no reason why liquid gallium should be more dense than solid gallium.

[ecoyte]

that's why ice floats on water!!

[ll_billym]

" the density is higher in the liquid state than in the crystalline state (like in the case of water; the opposite effect is normally found for metals). "

http://en.wikipedia.org/wiki/Gallium

http://www.madsci.org/posts/archives/2004-07/1089471606.Ch.r.html

http://www.reade.com/Products/Elements/gallium.html

 

 

 

[ll_billym]

There is probably more than 2 though.

[Gef]

Apolgies to ll_billym, Solid gallium is less dense than liquid gallium. Not sure of the reason though since it can be nothing to do with hydrogen bonding as in water.

[palfreyman18]

Water and Ammonia: They both have hydrogen bonding between then because of their lone pair of electrons. They use the Lone pairs to join with the hydrogens of other molecules of the same type. Because of this water and ammonia both have higher boiling points than expected but i cant remember exactly why they are less dense. There might be others though.