Ice is crystalline form of water. Ice has a highly ordered three dimensional structure containing hydrogen bond. X-ray studies show that each oxygen atom is surrounded tetrahedrally by four other oxygen atoms at a distance of 276 pm. One hydrogen atom lies in between each pair of oxygen atoms. So, each and every hydrogen atom is covalently bonded to an oxygen atom and linked to another oxygen atom by a hydrogen bond. This arrangement leads to a packing with large open spaces and results in lower density of ice than that of water. Hence, ice floats on water.