Here's why:
* Hydrogen bond formation: A hydrogen bond occurs when a hydrogen atom is attracted to a highly electronegative atom (like oxygen) in another molecule.
* Water molecule structure: Water has two hydrogen atoms and one oxygen atom. The oxygen atom has two lone pairs of electrons.
* Ice structure: In ice, each water molecule forms four hydrogen bonds. Two of these bonds are formed with the two hydrogen atoms of the water molecule, and the other two bonds are formed with the lone pairs of electrons on the oxygen atom.
This tetrahedral arrangement of hydrogen bonds is what gives ice its crystalline structure and explains its relatively low density compared to liquid water.
