Why does ice float?

Our atmosphere contains a number of gases, with a variety of relative atomic masses, including nitrogen (14), carbon dioxide (22), oxygen (16) and argon (18). Our atmosphere’s temperature can range from 50 degrees Celsius to -50 degrees Celsius depending on which layer you’re in.

Although water (9) has a considerably lower relative atomic mass than the Earth’s atmospheric gases, it is still a liquid at room temperature. You’d think that because of its low relative atomic mass, it would be harder for the molecules to bond at low temperatures. But water has to be heated up to 100 decrees Celsius to boil and freezes at 0 degrees Celsius, whereas the atmospheric gases are all gases at minus temperatures (although they have a higher relative atomic mass), which is uncharacteristic of molecules that size at those temperatures.

Impossible you say?

It’s all due to hydrogen bonding between the molecules. The oxygen molecules pull the electrons away from the hydrogen because it’s lack of electrons. Oxygen has 16 electrons meaning that it’s final electron shell is not full (having 6 electrons instead of 8) making it unhappy. To gain 18 electrons, the oxygen atom needs another 2, luckily the two hydrogen atoms both have one electron each, totalling up to the 18 electrons. The hydrogen also needs those electrons so the atoms are constantly fighting over them causing the hydrogen protons to be exposed which allows hydrogen bonding and is the reason for waters unusual boiling and freezing points.

ImageWhen water freezes, it causes a crystalline structure because of hydrogen bonding leading to a solid with a lower density than liquid water. This is why ice floats in a liquid, because it has a lower density.


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