Question

Why does water unlike other substances expand when cooled

Answer 1

In ice, each water molecule is surrounded by the four other water molecules with their oxygen atom occupying the corner of the tetrahedron. There are four hydrogen atoms attached to an oxygen atom; two of the hydrogen atoms are bonded by the covalent bond while another two by the hydrogen bond. This gives a huge 3D structure having large vacant spaces. Due to which liquid water expands while freezing.