Why does ice expand?

[Reggy]

With the recent weather that we have been having I was thiking about ice!

I thought I understood that gas' are where the particles are really spread out, water not so spread out, and solids even less. Therefore, when water turns to ice wouldn't it be correct to assume that the particles become closer together and, therefore, occupy less space?

However, when water freezes in pipes or bottles, etc. it expands and makes them crack...Any one know the science behind it?

[Clanad]

Scientists say water's quirky behavior is caused by the shape of its molecule and by how its molecules bond to one another.

Each water molecule is two hydrogen atoms bonded to one oxygen atom (H2O). Because of how the atoms share electrons, a water molecule is slightly positively charged at the hydrogen atoms, and slightly negatively charged at the oxygen atom. The molecule's charged ends attract the oppositely charged ends of other water molecules ("hydrogen bonding").

In liquid water, as molecules slip-slide past each other, bonds form, break, and re-form. But by the time water has cooled to 4 C., the molecules' energy has dropped enough that they are very near one another. So each H2O molecule forms more stable hydrogen bonds, with up to four fellow molecules.

By 0 C. (32 F.), the H2O molecules are snappily lined up in a frozen crystal lattice, an open hexagonal (six-sided) shape. Unlike in liquid water, the molecules in ice are held rigidly apart. That means more empty space between molecules, so frozen water occupies more room. (From our friends at Wierd Science)

[Gef]

Excellent answer from Clanad. This also explains why ice is less dense than water and so icebergs float and lakes freeze from the top down. If water froze from the bottom up then all life in the water would be killed and life might not have evolved on Earth.

[Reggy]

Thanks for the info, it certainly is weird! But i get an understanding for what is happening now. However, if the water takes up more space when it is frozen, then why is the ice caps melting a problem for increasing the water level? Is it because of the amount of ice above the water?

[JustSia]

Reggy, the problem is not just the rising sea levels but also the effect of all this melting ice on the dilution of the sea water (ie its salinity). This is believed to cause the change in water's temperatures and the Oceanic currents. Change the currents - change the climate. This is why there is so much upheaval regarding ice caps melting.

S.

[spacechimp]

Also Reggy, as you say, it's because such a large amount of ice is above sea level (on Antarctica and Greenland especially)

[4lec]

the melting of ice caps is only a problem if either the artic or antartica melt (sorry but cant remember off hand).
i just know that its only a problem when the one of them with land underneath melts.
This is because the one where the ice is floating is displacing more or less the same amount of water as is contained as ice.
the one where land (hard ground) is present underneath, obviously cannot displace land so melted water would have to run off into the sea, rising sea levels and diluting it as JustSia noted
im not saying this is fact, just something that i think i read in a textbook randomly one day
alec