Molecular Monday: Oxidation, Part Two

Molecular Monday is a special series here on Planet Pailly about the atoms and molecules that make up our universe, both in reality and in science fiction. Today, we’re continuing our investigation of oxidation-reduction reactions by taking a closer look at:


Most of us will remember from school that when atoms join together as molecules, they share each other’s electrons.

Ap09 Sharing 1

However, atoms don’t always share their electrons equally.

Ap09 Sharing 2

Chemists assign oxidation states to atoms within molecules to represent how many electrons each atom has effectively gained or lost in this unequal sharing.

An atom with an oxidation state of -1 has effectively gained one electron. An atom with an oxidation state of +2 has effectively lost two electrons. (Yes, positive numbers mean losing electrons and negative numbers mean gaining them. This is the convention we’re stuck with, even though it might make more sense the other way around.)

There’s a list of rules to guide you through the process of figuring out the oxidation states of each atom within a molecule. I’m not going to go through those rules here because a) it’s a rather long list and b) if you really want to see it, you can find it easily enough with a Google search.

Studying the rules for oxidation states reminds me of trying to memorize all the rules for comma usage in English grammar. On the surface, the rules seem simple enough, but then there are exceptions, and exceptions to the exceptions, and obscure situations that you’re told you’ll probably never encounter, but if you do enough writing and/or chemistry, I guarantee you’ll encounter those obscure situations eventually.

So oxidation states end up being somewhat messy and complicated, which reflects the rather messy and complicated reality of atoms. I remember getting frustrated in high school chemistry class because chemical reactions (especially oxidation/reduction reactions) never seemed to jive with my preconceived notions about atoms and molecules. But that’s an important truth about science: nature does what it wants and doesn’t care what you or I think about it.

I’m planning one more post on oxidation-reduction reactions. You can expect to see that two weeks from today. Then we’ll be moving on to some of the other chemical reactions that I found so frustrating in school.

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