Usually, most substances are denser in their solid state than in their liquid state, which causes them to sink. However, ice frozen from water actually floats! Why is this so?
Water is the most unique substance known to man. When water freezes at 0°C, ice would be formed which is less dense than liquid. Ice floating on water is related to hydrogen bonding.
A water molecule is made up of two hydrogen atoms (H) and one oxygen atom (O). The atoms of hydrogen and oxygen are bound by sharing their electrons with one another. This is covalent bond, since oxygen atoms pull electrons more strongly than hydrogen atoms, the oxygen atom in a water molecule has a slightly negative charge and the hydrogen atoms have a slightly positive charge. Hence, neighbouring water molecules are attracted to one another through the slightly negatively charged oxygen atoms and the slightly positively charged hydrogen atoms. This interaction is called “hydrogen bonding”. Hydrogen bonding is much weaker than covalent bonding however, this type of bonding has a large total effect because there are many hydrogen bonds.
Ice has a diamond structure due to the hydrogen bonding. Water does not have such anorderly structure, but water molecules are squeezed close to one another because of the hydrogen bonding. Thus, there is more space in ice than in water. This is the reason why ice is lighter than water. Now you know why Ice can float on water!
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