(This is a blog series on water, written by Priyadarshan Pandey.)

It’s World Water day! Is there a better day to start knowing more about me? I don’t think so!

Hello, there! I am your friend (cum creator cum nurturer) H2O, but you can call me Water. In this series of blogs, I will be telling you all about myself; past, present, and future. So come along and enjoy this journey (nay, voyage) as we explore the far seas of our understanding of nature, the life it sustains, and it’s most important cog, me.

You might be aware that I am somewhat essential for your existence (and by somewhat,  I mean that first primordial single celled beings, which evolved into all the life forms as you know them over billions of years, would not have been born without me). You must also have read how the earth is three-fourth water and so is almost every living thing on it. It is safe to say that regardless of your education level, economic background, and social status, you know how insanely awesome I am. So, instead of indulging in vainglory (although you have to admit I have earned some bragging rights) in this blog, I’ll be focusing on the reason of my importance and the chemistry which makes me special.

My uniqueness comes from my molecular structure. My one molecule consists of three atoms- 2 hydrogen atoms and an oxygen atom (thus giving me the name, H2O). Hydrogen atoms have one electron and need to either give it away or add another to their orbits to attain stability (although the latter is preferred as an electron less hydrogen atom is very reactive) whereas an oxygen atom has 6 electrons (8 in total) in its outermost orbit and needs to add another 2 to attain stability. In usual circumstances one of the atoms loses electrons and becomes positively charged, while the other gains those electrons and becoming negatively charged creating a bond of attraction between the atoms. This type of bond is called an ionic bond. But, since both the hydrogen and oxygen atoms, in this case, require the addition of an electron to become most stable they come up with another arrangement; they share. This type of bond is called a covalent bond, where an electron pair is shared between two atoms. Take a look at the illustrations below for better understanding.

You can see that the molecule is a little bent. This is due to the presence of 2 lone electron pairs in the outermost orbit of oxygen which exert a little extra repulsion on the two bonding hydrogen atoms to create a slight compression to a 104^obond angle.              Also, due to the vast difference in the size and electronegativity of hydrogen and oxygen atoms, the shared electron pairs are pulled closer to the oxygen atom than the hydrogen atom making them slightly negatively and positively charged respectively. This phenomenon coupled with the bent structure of the molecule creates a positive and negative charge on opposite ends of the molecule, making it polar. Thus, the covalent bonds in my molecules are called polar covalent bonds (not exclusive to water molecules).

Now that you have the basic understanding of my molecular structure let us dive into the oh-so coveted chemical properties this generates.

Polarity

My property of polarity is responsible for effectively dissolving other polar molecules, such as sugars and ionic compounds such as salt. Ionic compounds dissolve in me to form ions. This is important to remember because for most biological reactions to occur, the reactants must be dissolved in water. Because I am able to dissolve so many common substances, I was given the title the universal solvent. Polarity is why you are not able to mix me with oil (or other fats), because they are non-polar, non-ionic compounds that have strong covalent bonds. The substances with such properties make excellent containers for me, such as cell membranes and cell walls.

Hydrogen Bond

When my molecules align with each other, a weak bond is established between the negatively charged oxygen atom of one molecule and the positively charged hydrogen atoms of a neighboring molecules. The weak bond that often forms between hydrogen atoms and neighboring atoms is the hydrogen bond. Hydrogen bonds are very common in living organisms; for example, hydrogen bonds form between the bases of DNA to help hold the DNA chain together. Hydrogen bonds give my molecules two additional characteristics: cohesion and surface tension.

Cohesion

Because of the extensive hydrogen bonding, my molecules tend to stick to each other in a regular pattern. This phenomenon, called cohesion, is easily observed as you carefully overfill a glass with me and observe my molecules holding together above the rim until gravity overtakes the hydrogen bonding and the molecules spill down the side of the glass. Similarly, my cohesive property allows tall trees to bring me to their highest leaves from sources below ground.

 

Surface Tension

A special type of cohesion is surface tension. The tension on my surface occurs when my molecules on the outside of the system align and are held together by hydrogen bonding to create an effect similar to a net made of atoms. For example, the surface tension of water allows water spiders to literally walk on water!

Without surface tension, even the smallest objects would sink. The large particles of dust would not float, but instead would sink to the bottom and kill all of the marine life, causing the collapse of ecosystems. At the atomic level I help keep the cell membrane from collapsing on itself. My surface tension allows the cytoplasm to hold-up the cell membrane.

The importance of surface tension can be seen in your daily life too. Raincoats, for example, are able to keep me from soiling you and your clothes due to surface tension.

Thermal Properties

• High specific heat capacity– meaning that I need to gain a lot of energy to raise my temperature. Conversely I also needs to lose a lot of energy to lower my temperature. My specific heat capacity is 4.2 kJ/g/^oC
• High latent heat of vaporisation-which means a lot of energy is required to evaporate me. When I evaporate, I draw thermal energy out of the surface I’m on, which can be observed in sweating.
• High latent heat of fusion- meaning that at 0^oC I must lose a lot of thermal energy before I freeze, thus my liquid state can reach temperatures of down to -10^oC before it forms ice.

All the above points mean that a lot of energy needs to be gained, or lost, in order to change my temperature, and so the environment on the earth resists temperature changes that could cause the life forms damage. My high latent heat of fusion prevents the earth from freezing. You can see the huge part I play to keep the planet Earth habitable.

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So, that was today’s blog, my first ever. I hope you got some useful insight on not just why I am important for life on earth, but also the ‘how’ behind my versatile prowess. I must take your leave now. Until next time, fellas!