What substances are less dense when in a solid state than they are in a liquid state?

  1. In addition to water, for which the solid form (ice) is less dense than the liquid form, the element Gallium is also less dense in the liquid state. Gallium can be solid at room temperature but will melt in the hand.

confirmed as solid less dense than liquid:

  • gallium - 5.91 (solid) vs 6.095 (liquid)
  • bismuth - 9.78 (solid) vs 10.05 (liquid)
  • germanium - 5.323 (solid) vs 5.60 (liquid)
  • silicon - 2.3290 (solid) vs 2.57 (liquid)
  • water - 0.917 (solid) vs 0.998 (liquid)

claimed but probably false:

  • acetic acid - 1.266 (solid) vs 1.049 (liquid)
  • antimony - 6.697 (solid) vs 6.53 (liquid) (this "error" is repeated in many places, inc wikipedia)

Water is not always less dense in solid form. Depending on how the water crystals are formed, it may actually be more dense. Examples include HDA and VHDA.