☆ The Properties of Water

The Properties of Water

Water has a simple molecular structure consisting of an oxygen atom bound to hydrogen atoms by two single covalent bonds. Because of water's simple structure, the greater electronegativity of the oxygen atom makes the water molecule polar. Water carries two partial negative charges near the oxygen atom and two partial positive charges, one on each hydrogen atom, making water polar. The polarity of water allows the molecules to be cohesive, meaning they are attracted to one another. Each hydrogen bond is relatively weak; however, hydrogen bonds are important for the chemical organization of living systems and DNA. The polarity of water determines the chemistry of life and water's structure. Water's cohesion is also responsible for its surface tension. Water is also attracted to other polar or charged molecules (such as ions) as well. This attraction to other charged molecules is called adhesion. An example of cohesion or adhesion that the benefit of life uses is that plant leaves pull water upward from the roots, causing the seeds to swell and germinate. Another property of water is that it has a high specific heat.

Specific heat measures the extent to which a substance resists changing its temperature when it absorbs or loses heat. Hydrogen bonds absorb heat when they break and release heat when they form, minimizing temperature changes. Water's high specific heat aids organisms by helping maintain a stable internal temperature when external temperatures rise and fall and by helping prevent organisms from overheating due to the thermal energy released by chemical reactions inside cells.

Water also has a heat of vaporization. The heat of vaporization is defined as the amount of energy required to change 1 gram of a substance from a liquid to a gas. Many hydrogen bonds must be broken for water to evaporate. The evaporation of water cools down body surfaces.

Ice is less dense than liquid water because the hydrogen bonds in ice space the water molecules far apart. This is why icebergs can float. Because ice is less dense than liquid water, lakes don't freeze solid, allowing fish and other organisms to survive the winter. 

Water is also a good solvent for polar molecules. Polar water molecules are attached to ions and polar compounds, making them soluble. Because of water's solubility, many kinds of molecules can move freely in cells, allowing a diverse array of chemical reactions.

The last property of water discussed in this blog is hydrophobic exclusion. When nonpolar molecules, such as oils and fats, are put in water, they tend to clump together. This minimizes their disruption of the hydrogen bonding of water. This property is important for DNA, protein structures, and biological membranes.