Why Does Ice Float?
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Water is different. With most everything on Earth except freshwater,
the colder it gets, the more dense it becomes. Take alcohol for
instance. If we were to fill up a 1 liter container with pure alcohol at 30
degrees
Celsius (86 Fahrenheit) and then take another 1 liter container and fill it
with pure alcohol at 10 degrees Celsius (50 Fahrenheit) the cooler container of
alcohol would weigh more. This is because the cooler alcohol is more dense,
so more alcohol molecules can fit in the same container. This is true with
freshwater too, up to a point. But at about 4 degrees Celsius (40 Fahrenheit) water
reaches its densest point. Amazingly, as water cools further, it actually
becomes less dense.
Each water molecule is made of 2 hydrogen atoms and 1 oxygen atom. These are
connected to one another by very strong chemical bonds called
covalent bonds. Water molecules are connected to each
other by much weaker chemical bonds called
hydrogen bonds between the positively charged hydrogen
atoms, and one negatively charged oxygen atom in a neighboring water molecule.
As water gets colder than 4 degrees Celsius (40 Fahrenheit) the hydrogen bonds
connecting different water molecules adjust to keep the negatively charged
oxygen atoms apart. This results in a crystal latice which begins to form at
less than 4 degrees Celsius. This crystal latice is completely formed at
freezing, and is commonly known as ice.
So, why does ice float? Like most things that float, ice floats
because it is less dense than liquid water. Ice is about 9% less dense.
When ice forms, it takes up about 9% more space than it did as a
liquid. Thus, a 1 liter container of ice weighs less than a 1 liter container
of liquid water, and the lighter material floats to the top.
As we said, water is different.
Dragonfly Challenge:
Imagine a world where ice was more dense than liquid water. What would this
world be like? What would the consequences be for life in your local freshwater
streams and lakes. Write a story or an essay about this, and send it to us at:
Dragonfly@MUOhio.Edu
Jump Back Jack!