# Do any substances have the same density when solid and liquid?

I know that as you heat something it expands, but this is proportional to the change in temperature, so if I compare the density of a liquid right before freezing and right after then the thermal expansion would have a small effect.

However, when a material changes state the density can change rapidly. I know water gets less dense as it freezes, and I remember this is not typically the case, but do any substances have approximately the same density in both liquid and solid states?

• You could rephrase the question as: which substance has the smallest difference between the densities of its liquid and solid phase? Sep 28 '15 at 0:29
• Might help if you stated how close is "approximately" the same same density. I think that water has a relatively large change in density because of the formation of hydrogen bonds and that most materials undergo a much smaller change in density in going across their solid-liquid transition.
– user93237
Sep 28 '15 at 0:47
• A first order phase transition must have a volume change. Second order phase transitions need not. That's a start for you. Sep 28 '15 at 0:55

But as there actually isn't any universal and exact definition for the difference of solid vs. liquid, you might consider that Carbon $$C$$ and Helium $$He$$ as such a substances. This thought can be reasoned from their abnormal triple points. For Carbon there practically isn't a liquid form, and for Helium there isn't solid form. (which is stable in low pressure)