ElI5 what exactly happens in the freezing process that makes ice less dense than liquid water?

Question

ElI5 what exactly happens in the freezing process that makes ice less dense than liquid water?

In: Physics

Answer 1

Water molecules are slightly bent in a 105° angle, rather than the straight 180° angles of most other diatomic compounds. When most compunds freeze they settle into a compacted structure that rests completely stacked into itself (imagine a stack of uniform plates) which makes them more dense than their liquid form. Water molecules, however, form a tessalated structure that has large empty gaps in the middle between the different molecules that decreases the density of the solid form.