Why is ice less dense than water?

Why are elements and compounds usually more dense in their solid state than in their liquid state?

The density of ice is 0.917 g/mL, while the density of liquid water is 1.00 g/mL. What natural phenomena does this explain?

Density of Elements and Compounds in Solid and Liquid State

Elements and compounds are usually more dense in their solid state than in their liquid state. This is due to the arrangement of particles within the substance. In a solid state, the particles are closely packed together in a regular pattern, resulting in a higher density. In contrast, in a liquid state, the particles have more freedom to move around, leading to a lower density.

Water: A Notable Exception

However, water is one of the notable exceptions to this rule. The density of ice is 0.917 g/mL, while the density of liquid water is 1.00 g/mL. This difference in density can be attributed to the unique properties of water molecules.

Explanation: Why is Ice Less Dense than Water?

The molecules in water are more tightly packed than in ice, so water has greater density than ice. This phenomenon can be explained by the structure of ice crystals. In solid ice, the water molecules form a regular hexagonal lattice structure held together by hydrogen bonds. These bonds create spaces between the molecules, resulting in a less dense structure compared to the more closely packed molecules in liquid water.

Natural Phenomena Explained

The fact that ice is less dense than water has significant implications in nature. One of the most notable phenomena is the floating of ice on water bodies. Because ice is less dense, it floats on the surface of liquid water, insulating the water below and providing habitat for aquatic organisms.