A Student Authored Lab Manual
By Erica Choi and Christina Datuin
General Biology I
The Properties of Water
Have you ever wondered why ice floats in water, even though most other solids do not? Well, this is because when water freezes it expands because the molecules line up to form a very open crystalline structure that is actually less dense than liquid water; it's all thanks to hydrogen bonds! Water has many special properties similar to this one due to these bonds, and it’s a good thing that it has these special properties because they benefit the organisms living in water. For example, if water froze the way other liquids do, lakes and rivers would freeze solid and all the life in them would die.
Water’s chemical composition is H2O. The special properties of water come from the way that these atoms are combined together, thanks to hydrogen bonds, and also the way that they interact with each other. Hydrogen and oxygen also have a polar covalent bond because oxygen has a stronger pull than hydrogen, therefore making the hydrogen atom partially positive and the oxygen atom partially negative. Due to the partially positive and negative charges this causes the polarity of water to be relatively high, therefore water attracts other atoms because opposite charges attract. This allows water to dissolve other polar substances, which is one of the reasons why water is known as the universal solvent. Hydrogen bonds by themselves are weak, but when there are a significant number of hydrogen bonds together they can be very strong. So the molecules at the surface of the water "stick together" to form a type of "skin" on the water, strong enough to support very light objects. Insects that walk on water are taking advantage of this surface tension. Surface tension causes water to clump in drops rather than spreading out in a thin layer (example: the top of a glass of full water). Another property of water is that it is cohesive: water molecules stick to each other, and adhesive: water sticks to other substances. Water has a high specific heat and a high heat of fusion; this characteristic is significant because this means that water is extremely stable as a liquid.
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