You may say ‘it’s just water’ (dihydrogen oxide sounds plain silly)- it does not register on the senses, it is colorless, odorless, and tasteless. Yet when you are thirsty you seek it out and when you see it there is no better sight, when you drink it there is no sweeter taste. Even a scene in a film that depicts a traveler in the desert with parched lips evokes a response in most. We heave a collective sigh of relief when the oasis comes in sight.
Thirst is a sensation like no other.
If any one molecule is entwined into our deep sub consciousness its water. It is an essential and intricate part of the fabric of our bodies. It is the lifeblood of life. It is the lifeblood of the planet. No water, No life (at least as we know it).
What is so special?
- It is very stable.
- Amphoteric (can act as an acid and a base).
- Polar (explained below).
- Dissolves virtually everything (universal solvent).
- Interacts deeply with water loving molecules (hydrophilic) and refuses to interact with water hating molecules like oils (hydrophobic).
- Displays all three phases (solid, liquid, gas)* within a narrow range of temperature (0-100C). It is less dense as a solid than a liquid – ice floats.
- It has the ability to absorb a lot of heat, it is estimated that about 80% of global warming is absorbed by the oceans. The temperature of the earth’s biosphere is maintained through a narrow range through the aeons thanks to water.
- The ability by its surface tension and capillary action (to ability to move up narrow tubes against gravity) sustains vascular plants and trees.
- It transmits light fully in the visible part of the spectrum not only making it colourless but also allows the energy of sunlight to sustain life on the surface of the oceans.
*In the deep hydrothermal vents there exists a phase of water called super-critical water (intermediate properties between a liquid and gas).
To understand water one must understand a bit about how elements (such as hydrogen and oxygen) form molecules. (such as water).
What goes on at an atomic singles bar?
Unpaired electrons denote instability and increased reactivity (that is they can and do react with other elements and molecules. The electrons in the outermost shell of an atom that is not pair bonded is continually seeking another electron to pair up. It needs to find another electron in order to settle into a stable molecule.
Why this thirst for a relationship?
Octet rule – atoms like to be noble (or like a noble element) i.e. they all want to ensure that the outermost shell of their atoms has 8 electrons. If they do not naturally possess 8 electrons (like noble gases do), they will try to take or share electrons with other elements who are seeking a similar relationship. This fulfillment of the octet rule offers the most stable configuration – and electrons like humans yearn for this stable relationship – this leads to the formation of covalent bonds.
The 2 hydrogen atoms each have one electron. Oxygen has in its outer shell 6 electrons it needs 2 more electrons to satisfy the Octet rule. Presto! A perfect marriage. Only it is not a marriage of equal partners. The electron that is shared between the oxygen and hydrogen atom lies closer to the oxygen atom than the hydrogen atom as oxygen is able to attract this electron with more force towards its nucleus than the hydrogen atom. This means that the molecule of water (which has a tetrahedral shape) has one part of its structure (the part closer to the hydrogen atom) more positive than the part of its structure closer to the oxygen molecule. The water molecule is said to have an electrical dipole, the water molecule is polar**.
** (see cartoon – sorry, the Trekkie in me took over).
A special bond:
In addition to the sharing of the electrons between oxygen and hydrogen (the covalent bond) another bond exists in water. The polar nature of the water molecule ensures that interactions occur between dipoles. It is called a hydrogen bond***. This is what confers many of the unique properties of water.
** *hydrogen bond referred here should not to be confused with the covalent bond – (the hydrogen bond is weaker than the covalent bond but far more important in geochemistry and biology). It exists between molecules of water, between different parts of the water molecule itself and its interaction with every chemical (organic or inorganic) directs everything on our planet from the regulation of temperature to allowing life to form.
How do you feel thirst?
The tonicity of the water content of the blood (plasma osmolality) is a measure of the concentration of dissolved ions (principally sodium in health). As the water content of the body goes down, it changes the relative amount of these ions i.e. Increases the concentration (increased plasma osmolality). This change is perceived when the fluid washes against a part of the brain called the hypothalamus (the thirst centre). There are 2 other areas in the brain – just so that such an important regulation is not done by only one place). This make you want to drink and if you listen closely to the thirst reflex – drink only till the sensation passes you will return the plasma osmolality to its normal value.
Normally other dissolved substances such as glucose, urea etc. are in equilibrium with cells, but diseases such as diabetes, liver and kidney failure can alter the plasma osmolality and alters body function.
Water, water everywhere………
The planet is 3/4ths water. Our bodies are 3/5ths water, the fluids outside are cells e.g. blood are 7/10ths water. Water has been found around a distant quasar (APM 08279+5255), the oldest (12billion years old)body of water – just a little over a billion years after the Big Bang, it is also the largest body of water (estimated to be 140 trillion times the volume of the earth’s oceans). http://www.nasa.gov/topics/universe/features/universe20110722.html
………but clearly not enough for everyone.
Water conflicts rage in many parts of the world. It happens between countries (Jordan and Syria, Egypt and Ethiopia, India and Pakistan, India and China) and within countries (US, India). There have been numerous ominous reports that future conflicts between nations may have water sharing as its root cause.
- Aboard the USS Chemical Enterprise
paulramesh 
#1 by Sivasubramanian Sivarajan on January 5, 2014 - 10:36 am
Until recently, I didn’t know there were “world experts” on water! Prof.Martin Chaplin is one of them – http://www.nature.com/nrm/journal/v7/n11/abs/nrm2021.html He says, “Liquid water is not a ‘bit player’ in the theater of life – it’s the headline act”
#2 by paulramesh on January 5, 2014 - 1:07 pm
absolutely Siva.
you may be interested to know that a fair amount of research and debate goes on as to the real nature of these hydrogen bond interactions, no means a settled question. http://www.pnas.org/content/110/39/15591.abstract
#3 by emmanuelrajasingh on January 6, 2014 - 12:17 pm
Hi sir, that was very interesting… it made me think… and the following questions are the result of my thinking.
1. Why do water expand on cooling to ice. .?
2. Why does flowing water never freeze even at negative temp. ?
3. Why doesnt water on cooling become ice completely? Like in lakes and ponds, the upper part is ice but the lower part is still water.. even in Antarctica the iceberg floats on water below. .. But the temp is very much negative. ..
#4 by paulramesh on January 7, 2014 - 4:12 am
in reply to Emmanuel’s query:
this is also due to the hydrogen bonds.
normally when a substance goes from liquid to solid the atoms or molecules of the substance get closer and closer ( that is more and more dense) . the intermolecular forces in most substances can be easily overcome as they are compressed. Water is very unusual – it is most dense not at 0 degree C but at 4 degree C. the hydrogen bonds hold the water molecules apart and makes the water at 0C to be further apart than at 4C. thus water occupies 9% more space(volume) at 0C – making it less dense – making it float.
If ice was heavier the lakes would freeze bottom up – and no life would be possible in winter.
when water flows – there is a kinetic energy and mixing with water of different temperature so it will be at a higher temperature than the surrounding and does not freeze – as it gets colder it will eventually freeze once its temperature reaches zero.