Why does ice float?

[the tree]

Hot stuff goes up and cold stuff goes down right? Hence pretty convection currents and plate techtonics and all that jazz.

 

But if this is so then why does ice float in water considering that the ice is probably less than 5 centigrade and the water (from the same tap) is room temperature?

[mmalluck]

You must ask yourself why does hot air rise and cold sink to begin with. The answer, my friend, is density.

 

When water freezes, it forms crystals. These crystals take up more space than liquid water normally would. The same amount of matter, but more space equates to a lower density.

 

It's the same reason why you shouldn't freeze water in a glass container. The ice expands (as well as becoming less dense) and cracks the container.

[ydoaPs]

water is one of the wierd compounds that gets bigger as it freezes. same mass with different volume means different density.

[Bettina]

Because at the freezing point of water, molecules form a crystal latice structure that has air gaps. This makes the ice less dense than liquid water and so it floats.

 

Bettina

[Skye]

It doesn't have air gaps as such, there's nothing in the gaps between the molecules (crystal defects aside).

 

It's like mmalluck said, basically the water molecules form a hexagonal crystal structure upon freezing, something like a honeycomb. This takes up more space than if the water molecules are all jumbled together as in liquid water.

[TheGeek]

the best way i can explain this is with a simple example.

If you place a pop can in the freezer it expands and if it stays long enough in the freezer it will explode.

Frozen pop takes up more room then liquid pop just like ice takes up more room then water. Because it takes up more room it has a lower density.

[YT2095]

water expands 11% upon freezing, making it 11% less dense than water, and so 11% of it will remain above the surface and the other 89% underwater.

 

simple as that really

[mezarashi]

I'd just like to add an interesting fact. Water molecules H2O consist of 2 hydrogen and 1 oxygen atoms which form covalent bonds at about 104.5 degrees (making it polar as well, a good solvent). It is because of this unique structure, the hexigonal crystal structure forms upon freezing as this minimizes the energy between the hydrogen bonds.

 

Also, it is because this great property of water, expanding upon freezing that makes life on Earth possible (well not to mention the fact that we are 75% water). The coldest depths of the ocean is at about 4 degrees Celsius as this is the temperature in which water is most dense. When it gets any colder, the water slowly rises where sunlight will heat it up again. If water were to increase in density upon freezing (as with a majority of common substances), we will find that ice will start accumulating on the ocean floor and slowly the world will freeze over.

[swansont]

The coldest depths of the ocean is at about 4 degrees Celsius as this is the temperature in which water is most dense. When it gets any colder, the water slowly rises where sunlight will heat it up again.

 

 

Or in other places it freezes, and the layer of ice acts as insulation. So lakes don't freeze up completely, and fish can live in them over the winter.

[the tree]

Wow, thanks everyone. I can't belive I just learned all that from asking such a simple question!

[H2SO4]

water expands 11% upon freezing' date=' making it 11% less dense than water, and so 11% of it will remain above the surface and the other 89% underwater.

 

simple as that really [/quote']

 

 

 

Wow, realy. thats alot of expansion!

 

I believe bismuth expands 4% upon freezing. The crystals are also less dense, so they float, just like water, but alot hotter.

[BigMoosie]

...the ice is probably less than 5 centigrade...

 

I'd say it is probably less than zero centigrade.

 

...and the water (from the same tap) is room temperature

 

You should get a better water system then because my water is probably closer to your estimate of ice.