LET’S TALK WATER -- #2

What is Water, Anyway?

As the earth formed, there was present an abundance of different atoms including hydrogen and oxygen gas. These two elements easily form a covalent molecule because the outer ring of the oxygen molecule has six electrons leaving room for two more.

 (Some caution is in order here; the illustration above shows a concept suggested by Niels Bohr, which is very useful because it helps us understand and predict chemical reactions among atoms. Physics has since determined that atoms/molecules are too complex in their behaviour to be rendered visually, one-dimensionally)

 Hydrogen being the simplest atom known has only one electron on its outer ring, so when molecules of hydrogen are in the vicinity of oxygen, the oxygen and hydrogen atoms are able to make a deal to share electrons, thereby creating a more stable molecule than each possess separately. 

Although hydrogen is by far the most abundant element in the universe, it exists mainly in molecular bonding with other elements, water being the main one here on earth. The covalent molecule of one oxygen and two hydrogen atoms is what we call “water.” We could call it “di-hydrogen oxide,” but to yell at the dinner table, “Please pass the Di-Hydrogen Oxide” would sound silly.

The earth, for all practical purposes, is a closed system; theoretically, its mass is only increased if it collides with another object in the solar system and its mass is reduced only if we shoot something out of the earth’s orbit. Water is subject to neither of these to any appreciable extent, so the total amount of water on earth remains relatively the same—again, for all practical purposes.

But the water cycle is an open system inside a closed system; energy is repeatedly absorbed and given up so that water evaporates into mist, condenses and falls again as water, a never-ending cycle.

When we talk water, we’re normally referring to liquid water.  The state of the water for washing and drinking—as opposed to fog, clouds and invisible vapour—is fluid (pardon the pun): water and water vapour molecules are in free vibration but when enough energy is removed by cooling, condensation produces liqued water. When molecular vibration in liquid water slows down due to further cooling, it turns to its solid state: ice. 

When water vapour is cooled to below zero degrees Celsius, molecules coalesce into snow crystals, their shape a product of the construction of the molecules themselves. It's still water, but called "snow."

We can separate the hydrogen from the oxygen of a water molecule by passing an electric current through it. That’s why the production of enough hydrogen to be used as a medium for driving cars and buses is best located near a hydro dam. In a hydrogen-driven car, the hydrogen molecules reunite with oxygen atoms to return it … you guessed it … to water. 

Tearing the water molecules apart through hydrolysis takes energy; in a car engine, this energy is returned as the hydrogen “burns,” or "oxidizes," and the resulting water drips from the exhaust pipe. 

(Note: If you have trouble believing this, go to Hydrolysis (eircom.net) and split some water molecules yourself.)

Far more interesting, probably, is how water changes states in the process of plant growth, how plants steal hydrogen from water to make the carbohydrates that provide their energy for growth and spit out excess oxygen during the day when photosynthesis is taking place. Also, how they steal Carbon dioxide from the air because carbon is the main ingredient in carbohydrates, thereby doing their part in saving the planet from climate change. But all that's another story. 

Look for the next episode: "So What's the Problem?"