We know for a fact that when matter is heated, its molecules expand and when matter is cooled, its molecules compress.
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But with water, it is a little bit special.
When water is cooled especially in winter season, just like any other matter, the molecules of water compress however at a temperature approximately 4 degrees Celsius the molecules of water start to expand and solidify forming ice until it reaches the freezing point. This is unusual because solid form of liquid is expected to be tightly packed.
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Left : Iced water in liquid water
Right: Benzene ice in liquid Benzene
Why is this so?
There comes the amazing property of water. When water slowly turns into ice at temperature approximately 4 degrees Celsius, its hydrogen atoms will create a network where it lines between two oxygen atoms. This network becomes stronger and stronger as the temperature drops. Because of this network, there will be more spaces between the molecules as supposed to be tightly packed with each other like other liquids do. This open spaces make iced water less dense than liquid water causing it to float.
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Left: Molecules of liquid water
Right: Molecules of iced water
This is why during winter season, the surface of a river, lake, sea or ocean is the first to solidify instead of the bottom.
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Now what makes it special?
If water continues to compress as it solidifies, Ice would be denser than water, this would make ice sink in the water and if this is the case, the bottom part would solidify first going upwards and this would freeze the entire body of water killing all the life forms in it and life wouldn't have existed.
That is how special water is, it definitely is the life of this blue planet.
Isn't that Amazing??
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