Alan Stahler: No water, no life
Atoms are the tiny bricks of which the world is made.
Every atom has a nucleus at its center, and a cloud of electrons whirling around that nucleus.
All electrons carry a negative electrical charge, keeping them bound to the positively-charged nucleus.
Being similarly charged, electrons “feel” each other ” repel each other ” as they buzz around in the cloud. And they feel the positively-charged nucleus, pulling them inward.
Some electrons spin through regions of the cloud close to the nucleus, other electrons spin farther out. Electrons close to the nucleus feel its pull more strongly; electrons farther from the nucleus feel it less.
Every type of atom ” oxygen, carbon, nitrogen, etc. ” has a specific number of electrons in its cloud ” exactly enough to counterbalance the amount of positive charge carried by its nucleus.
With different numbers of electrons, pushing and pulling on each other, and with nuclei of different strengths pulling electrons inward, each type of atom’s electron cloud is a unique environment. Some clouds hold onto their electrons more or less tightly than others.
Different electron cloud environments give each type of atom its own “personality.” Some atoms ” sodium, for instance ” shed electrons at the drop of a hat. Other atoms ” chlorine, say ” greedily snatch electrons off other atoms.
Suppose a sodium atom, with a yen to lose an electron, meets up with a chlorine atom with a desire for more. The chlorine grabs for the electron, which the sodium happily yields. We now have two ions: A sodium ion, missing a negative electron, and a chloride ion with an extra electron.
With one negative electron gone, the sodium ion now has a positive charge. With an extra electron, the chloride ion now has a negative charge.
The positive sodium and negative chloride ions attract each other strongly – so strongly that, to separate them, we need to heat them to nearly 1500 degrees Fahrenheit – the melting point of sodium chloride.
Which is unfortunate, because we need sodium to live, and there’s no way our bodies can deal with temperatures of 1500 degrees.
Oxygen atoms are even more hungry for electrons than chlorine. And hydrogen atoms don’t mind losing an electron – though they’re not as careless with it as sodium.
When hydrogen meets oxygen ” when hydrogen burns – the oxygen makes a grab for the hydrogen’s electron, but can’t steal it away completely. Rather, the two atoms share the electron.
Not satisfied with just one, the oxygen atom finds another hydrogen atom, makes a grab for its electron, and winds up sharing that one, too.
By sharing electrons, two hydrogens and an oxygen bond to form H2O ” water.
Because oxygen craves electrons much more than does hydrogen, the sharing is not equitable: The oxygen atom holds the electrons close, allowing them to visit the hydrogens only now and then.
The water molecule has an oxygen atom on one end, with two extra electrons hanging about. At the other end of the molecule are two hydrogen atoms, visited only occasionally by the electrons they’ve brought to the molecule.
With two negative electrons hanging about most of the time, the oxygen end of the water molecule is more negative than the hydrogen end; the hydrogen end is more positive.
Positive on one end, negative on the other, water molecules can attract both positive sodium ions and negative chlorides. Water molecules can thus slip between the ions in a crystal of salt. Surrounding an ion, the water molecules gently pull it away from the crystal.
And they does this all at room temperature.
Water has many properties that make it useful to biology; its ability to gently dissolve salts makes it indispensable.
Up to now, all indications of water on Mars have been circumstantial. But over the past several weeks, the Phoenix lander has been excavating and analyzing soil in the Martian arctic.
Phoenix has ” almost literally ” tasted water.
Future missions will search for evidence that Martians ” single-celled Martians ” might once have existed… or might still exist. If there were no water on Mars, there would be no reason to search.
Alan Stahler’s science program can be heard on KVMR radio (89.5 FM) next Tuesday at noon. He offers tutoring and enrichment classes for students of all ages; call 470-8937.
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