As a preface to this entry, I'm going to write about my first real experience with what I now call the master vampire element, oxygen. At the time, I was working on a different approach to etching gold. Since gold is a relatively inert element, it takes some doing to etch it -- basically, turning the metal into a salt of some kind. I was thinking about gold chloride. Aqua Regia is a commonly-used etchant for gold, made by mixing nitric acid and hydrochloric acid. Thing is, the mixture is unstable because the two acids react to form something called Nitrosyl Chloride -- and it quickly decomposes. It also takes some time for NOCl (its chemical formula) to form so you're running a race between getting the etchant working and then using it before it decomposes. There also are a number of different ratios given for the ingredients, probably because they come in a number of different concentrations. So I had some interest in coming up with something that was more stable and more reproducible. I had concentrated hydrochloric acid available, the same with 30% hydrogen peroxide, so I had the thought of combining the two to see how that would work. The idea was that the peroxide would oxidize the gold and then the acid would react with the oxide to form its chloride.
Well, my new etchant sort of worked but it turned out to be even more unstable than aqua regia. The REALLY interesting part was that my mixture quickly decomposed by releasing a green-yellow gas: chlorine. Well now, what was that about? It didn't take long for me to realize that the hydrogen peroxide had done it, using its extra oxygen atom to grab two hydrogen atoms from two molecules of hydrochloric acid (HCl), forming one molecule of water and one molecule of Cl2. Up to that point, I had thought that chlorine was a pretty strong oxidizer and was pretty safe from being affected by oxygen: but my little experiment blew that notion right out of the water. BTW I performed my experiment with just a small quantity of the two materials, under a fume hood so no harm done.
Now I want to talk a little about the idea of "valence". Fundamentally, it means how many electrons an element in a compound has either gained or lost: or wants to gain or lose. Many reactions are all about electrons. For instance, in the water molecule we have two atoms of hydrogen and one atom of oxygen. Oxygen has a valence of 2, because it "wants" two additional electrons to fill its outer shell (and each hydrogen atom only has one to provide, so it takes two to form a stable molecule). And oxygen REALLY wants those electrons, as shown by my little experiment.
It gets even more interesting though. Looking at chlorine (Cl), it has a valence of 1 when it combines with things like sodium to form sodium chloride, table salt. In that case chlorine is the oxidizer and sodium is the reducing agent. But oxygen is such a powerful oxidizer that it can actually wrest electrons _away_ from chlorine, which in itself is no slouch as an oxidizer. In fact, oxygen is so powerful that it can abduct SEVEN electrons from chlorine, forming perchlorate compounds. They are used to make explosives in fireworks. Perchlorate compounds themselves are extremely powerful oxidizing agents, so if mixed with things like charcoal and sulfur they are more than ready to go boom. Perchlorates are not the only ones that are infected by the bite of oxygen. Chromium trioxide (CrO3) is notable because it is in a +6 oxidiation state (3 * oxygen's valence-of-2 = 6). Squirting acetone on a pile of dry chromium trioxide powder will instantly cause the acetone to burst into flame because it's just ripped apart by the combination of hexavalent chromium and oxygen. Another good one: the permanganate ion. In that one, manganese is in a +7 oxidiation state. By now it shouldn't be much of a surprise that it also is an extremely powerful oxidizer. It will react with a sugar solution at room temperature and turn it into black sludge in very short time. When bitten by oxygen nitrogen suffers a similar fate and as a result becomes usable for things like explosives (think nitroglycerine) and rocket fuel.
In these instances, the base elements -- chlorine, chromium and manganese -- range from being a fairly powerful oxidizer to "not in my wheelhouse" -- but oxygen bites 'em and they turn into vampires themselves. That's why I call oxygen the master vampire, because it can affect otherwise innocent elements and turn them into monsters, too.
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