Ice Floats

Why Does Ice Float?

Ice Floats - Moving ForwardThe fact that ice floats is extremely important to life on earth.

If it didn’t, ponds would fill with ice from the bottom up, leaving fish haplessly exposed to predators on the surface.   Polar bears, penguins, seals and walruses would have a different lifestyle.  And people probably wouldn’t have found it convenient to learn to ice skate either.

But why?  We usually think of solids being more dense and sinking to the bottom.  So why is water different?

Water is a strangely shaped molecule…

It’s lopsided.

As you know each water molecule is really made up of one oxygen atom and two hydrogen atoms (H20).  You would think that since those 2 hydrogen atoms are both positively charged, that they would arrange themselves to stay as far away from each other as possible.

But they don’t

That oxygen atom and 2 hydrogen atoms combine into an L shape, with the slightly negatively oxygen on one side and the 2 slightly positive hydrogen atoms on the other.

When water is still liquid, the molecules just bump around in any old configuration.  But when water freezes, the molecules try to line up with the positive side of one molecule facing the negative side of the next molecule, the way magnets do.

Ice in Drink - Moving ForwardThat takes up extra room.  So unlike most other substances, when you freeze water it expands, meaning that the same volume of ice weighs less than water.  And therefore ice floats.

Whether it is in your tall, cold drink or in the Arctic Ocean, ice does float.   And now you know why.


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