At about 4 degrees Celsius, dihydrogen monoxide molecules are arranged in their lowest density position due to hydrogen bonds that align them in a perfect crystalline fashion. Once frozen, these molecules retain this density. Water near freezing but not solid can be agitated and therefore does not stay at this perfect low density position and being denser "sinks" below the ice.

I read the information at the following link http://chemistry.about.com/od/chemistryfaqs/f/icefloats.htm and here's my summary: The reason ice floats is because of its density in relation to the density of water. Rocks, for example, sink in water because rocks are more dense than water. The action of the rocks sinking is also known as displacement. Ice, on the other hand, is less dense than water - about 9% less dense. The reason water becomes less dense as it freezes is due to a chemical process called hydrogen bonding. Anyway, because ice is less dense than water, it weighs less than water. If you filled up a gallon (US) jug with water, the water would weigh roughly 8.34 pounds (US). After the water froze, however, the gallon of ice would weigh around 7.5 pounds. http://wiki.answers.com/Q/How_much_does_a_gallon_of_ice_weigh In a glass of ice and water, the heavier water displaces the lighter ice and sinks, like the rocks did in the first paragraph. And that, in a nutshell, is why ice floats on water. I hope this helps.

Water has peculiar property that other compounds don't. When something goes down in temperature is contracts so it get more dense and won't float. Water however when it start to freeze, instead of contracting it expands, becoming less dense. Since ice weighs less than the water it displaces, it floats in water.

thought to ponder-you have many good answers here points for all-if ice didnt float life as we know it wouldnt exist on this planet-the ice would settle to bottom and eventually build up till most of the water on this planet would be frozen---smile and enjoy the day

Roughly speaking, ice contains about 10 percent air. The air gives the ice ''bouyancy''. Place an ice cube in water, the amount of cube that sticks out of the water represents the ''volume'' of air contained in the cube.

I found the answer on google search. Answer: The reason why ice is lighter than water is that a certain mass of ice occupies more space than the same mass of water. This is related to “hydrogen bonding”. Hydrogen bonding A water molecule is composed of two hydrogen atoms (H) and one oxygen atom (O). The atoms of hydrogen and oxygen are bound by sharing their electrons with one another. This bond is called a “covalent bond”. However, since oxygen atoms pull electrons more strongly than hydrogen atoms, the oxygen atom in a water molecule has a slightly negative charge and the hydrogen atoms have a slightly positive charge. So adjacent water molecules are attracted to one another through the slightly negatively charged oxygen atoms and the slightly positively charged hydrogen atoms. This interaction is called “hydrogen bonding”. Hydrogen bonding is much weaker than covalent bonding, however, this type of bonding has a large total effect because there are so many hydrogen bonds. Structure of ice and water Ice has a diamond structure due to the hydrogen bonding. Water does not have such an orderly structure, but water molecules are squeezed close to one another because of the hydrogen bonding.

The simple, easy explanation: Water is one of the only liquids that expands when it freezes. Because it puffs up bigger when it's solid ice, it weighs less than water. And anything that weighs less than water ... will float on water.

Ice floats on water because of the exeptional property of water known as 'anamolous expansion of water'.Normally most liquids contract on cooling.This is also in case of water upto 4 degree celsius.But when water is cooled below 4 degree celsius it expands instead of contracting.Naturally it's density decreases.So when ice is immersed in water,the weight of water it displaces is greater than the weight of ice.Thus it gets an upthrust which enables it to float on water.