Image shows whales and ice floating on water

Have you ever stopped to think how interesting it is that ice floats on water? Solids are usually denser than liquid because the atoms are closer together. Therefore, in most substances, the solid form would sink when placed in the liquid form.

 The image shows the molecular arrangement of a solids, liquid and gas

Learn more about why the solid form of water is less dense than the liquid form.

Video segment. Assistance may be required. Watch the following video to see how water molecules are held together by hydrogen bonds due to the molecular polarity (charged ends of the molecule).

Source: Hydrogen Bonding Video, mtchemers, YouTube

Interactive exercise. Assistance may be required. Let’s review what you learned from the animation. Answer the questions below.

Hydrogen bonding occurs in many compounds, not just water. Hydrogen bonding occurs between any compounds where hydrogen is bonded to N, O, or F on one molecule, and a neighboring molecule has a lone pair of electrons on an N, O, or F.

Below is a cartoon representation of hydrogen bonding.

Answer the following question.

Why is the solid state of water less dense than the liquid state of water?

Interactive popup. Assistance may be required.

Check Your Answer

Water molecules are attracted to each other due to hydrogen bonds. In the liquid state, the molecules have greater freedom of movement and hydrogen bonding can hold the molecules very close to each other. In the solid form, the hydrogen bonds between water molecules still exist, but they are not as strong, so the water molecules move further apart which decreases the density. Close Pop Up