The Properties of Water

Water...agua...H2O. However way you say it, water is the same anywhere you go. It is a life source to not only us humans, but to other organisms out there, as well. In biology, it is so much more.

Today I am going to talk about the different properties of water. There are four main properties specifically that I am going to touch on: cohesive/adhesive behavior, ability to moderate temperature, expansion upon freezing, and versatility as a solvent. However, before I begin to talk about water, I feel that I should go over some things about polarity and hydrogen bonding in order to fully understand these four properties.

Water molecules are polar. That is a fact. But why are they polar? Well, they are polar because of this little thing called unequal sharing. The oxygen in the water molecule attracts the two electrons from the hydrogen, one from each. Now, why are water molecules capable of hydrogen bonding with four neighboring water molecules? Well, for starters, a hydrogen bond has the ability to take a positive side hydrogen and a negative side oxygen, and create a bond between them. It is a weak bond, but it is still bale to keep water together. This entire process is called cohesion, but we'll get back to that later. You see, because the oxygen has a 2- charge, it can attract two hydrogen atoms from two other water molecules. And each hydrogen can attract one oxygen atom, which makes two more water molecules. In total, that makes four neighboring water molecules.    

Alright, now that we have gone over that, let's talk about cohesive and adhesive behavior. Cohesion is the ability of water molecules to be able to bond to each other. In other words, hydrogen bonding! An example of cohesion is how insects like water striders can walk on the surface of a pond without breaking the surface. Although the water strider is denser than water, it doesn't sink. This is because of surface tension and cohesice behavior. The ability of cohesion to keep water together allows the water strider to sit and walk on top of those hydrogen bonds.



Adhesion is the ability to have water attached to something else. For example, if a straw has a negative charge, water is able to bond along the straw. This is called capillary action, the ability of a water molecule to do adhesion and be able to move up a straw. The bigger the straw, the less capillary action.

Capillary action is also very important in plants. Plants transport water from the roots all the way up to the leaves. For this process to occur, both cohesion and adhesion are needed. So, the water begins to come up from the roots. In order to go up to the leaves, the water molecules stick along the plant; this is where adhesion comes into play. Cohesion occurs when the water molecules going up the plant begin to stick and attach themselves to each other. You see, both cohesion and adhesion are working here at the same time. In a tree, the water molecules would go up along the trunk tubes inside the tree until it reached the top, where the leaves are. However, not all of the water stays on the leaves. Water on a leaf can easily evaporate (turn from liquid to vapor) through the leaves' pores. Ninety percent of the water sucked in by the roots is lost at the surface of the leaves at the top of the tree or plant.

Water also has the ability to moderate temperature. It is able to resist temperature changes due to hydrogen bonding. Hydrogen bonds are able to break and be created, and in order for water to increase in temperature the hydrogen bonds must break. By doing this, the water rises to its high boiling point. The hydrogen bonds can also release and take in some energy. This entire property of water allows bodies of water to maintain temperatures by storing heat from the sun and by releasing heat when the air around it gets cooler. Different materials store different amounts of heat. Let's take gold and water, for example. Water takes about thirty times longer to heat than gold, which means it stores about thirty times more calories. 

Just as water can heat up and boil, it can also freeze! When water boils, the molecules begin to move rapidly. Furthermore, when water freezes, the molecules slow down and once the hydrogen bonds get to a certain temperature, they become stable and form a crystalline pattern. This crystalline pattern is very "open," causing the water, now ice, to become denser than liquid water. There is less mass, but the same amount of volume, and for this reason, ice floats. 


One last thing to know about water is that it is known to be a versatile solvent. It is sometimes know as the "universal solvent." Water is capable of dissolving with more materials than any other liquid. It is such an effective solvent because it readily forms hydrogen bonds. For instance, let's take a lysozyme molecule in a nonaqueous environment. The moment you add water, you get different polarities. This causes the hydrogen bonding. Your result will look like salt. The water molcules begin to split up the NaCl into smaller pieces. When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules, a hydration shell.

These are only some of the many things to know about water. I'm sure there is more I could tell. For instance, how hydronium and hydroxide are the products of the dissociation of water. Or how their concentration in pure water is 1e-7 M. But for now, this is all I can say. Until next time!