Why does water exhibit anomalous behavior near its freezing point?

[Badfish97]

So as some of you already probably know, water exhibits anomalous behavior when its temperature increases from 0°C to 4°C (it contracts) and when its temperature is decreased from 4°C to 0°C (it expands). Why does this happen?

 

[jajabinker]

When water is ice (0°C) it has a structure that has a lot of empty space in between, due to the low temperature and symmetrical hydrogen bonding.
http://www.uic.edu/classes/bios/bios100/lectures/02_15_hydrogen_bonding-L.jpg

In the liquid state there is a more irregular pattern for hydrogen bonding, but far from random.

As you decrease the temperature of a liquid,the density increases, for most materials. But as water goes below 4 degrees, there is a phase transition where these hollow structures form(like Ice 1h), which now reduce the average density of water.

 

[Badfish97]

When water is ice (0°C) it has a structure that has a lot of empty space in between, due to the low temperature and symmetrical hydrogen bonding.
http://www.uic.edu/classes/bios/bios100/lectures/02_15_hydrogen_bonding-L.jpg

In the liquid state there is a more irregular pattern for hydrogen bonding, but far from random.

As you decrease the temperature of a liquid,the density increases, for most materials. But as water goes below 4 degrees, there is a phase transition where these hollow structures form(like Ice 1h), which now reduce the average density of water.

So you're saying that when its temperature increases from zero degrees to 4 degrees, the irregularities in its hydrogen bonding increases, therefore it becomes denser?

 

[jajabinker]

Yes.
Let me show you a video
Notice how the black spaces disappear. i.e. more number of molecules per black space appear. Which is roughly your density.
This comes from molecular dynamics simulations. Great care has been taken over scores of work hours to ensure this is a realistic model.

Its rather intuitive.

 

[PJC01]

The anomalous behavior of water at temperatures close to its freezing point is due to its unique molecular structure. Water molecules are polar, meaning they have a positive and negative end, and are able to form strong hydrogen bonds with each other.

At temperatures below 4°C, water molecules start to arrange themselves in a hexagonal lattice structure, which causes the molecules to be more densely packed and therefore more compact. This results in a decrease in volume and the contraction of water.

As the temperature increases from 0°C to 4°C, the thermal energy breaks down the hydrogen bonds and disrupts the hexagonal lattice structure. This allows the molecules to move more freely and increases the volume of water, resulting in expansion.

This anomalous behavior of water is important for many biological and environmental processes. For example, the expansion of water upon freezing allows for the formation of ice on the surface of lakes and rivers, insulating the water below and providing a habitat for aquatic organisms during winter.

Furthermore, the contraction of water at low temperatures allows for the existence of deep, cold water bodies, which are crucial for ocean circulation and the transport of nutrients and oxygen to deep sea organisms.

In conclusion, the anomalous behavior of water is a result of its unique molecular structure and has significant implications in various natural phenomena. Further research on this topic can lead to a better understanding of the behavior of water and its role in the environment.