Mole Day 10/24/19

On science by Richard Bleil

*Editorial Note:. When I wrote this, I had the wrong date in mind. Avogadro’s Number is 6.02×10^23 (not 24). As such, National Mole Day was yesterday, not today. I apologize F r this error and any confusion it may have caused.

Happy Mole Day.

Well, maybe. If you are reading this between 6:02 AM and 6:02 PM, today, October 23, you’re reading it on National Mole Day.

I first read about National Mole Day, much to my chagrin, buying a McBurger at a fast food joint that shall to unMcnamed.

Okay, so let’s chat a bit about this. National Pi Day is the brainchild (I assume) of the American Chemical Society for the purpose of promoting awareness of chemistry. National mole day is based on Avogadro’s number. Avogadro figured out relative masses; oxygen is 16 times heavier than hydrogen, so if you have 1 gram of hydrogen, and 16 grams of oxygen, you have the same number of oxygen atoms as hydrogen atoms. Avogadro didn’t know what this number was, but he chose to call it one “mole”. Don’t ask me why; maybe he liked blind burrowing furry critters. Later, it was determined that this number happens to be 6.02×10^23 (6:02, 10/23).

My students struggle with what a mole is. It’s just a number, nothing more. One mole is one mole, regardless of what it is that you are discussing, just like a dozen is 12. Twelve what? Twelve of whatever it is you mean; it’s just a number.

I’ve often thought of the roots of chemistry to be the Greed philosophers, “The Atomists”, dating back to around 900 to 500 B.C. They hypothesized the existence of elements, and believed there to be four of them (earth, wind, fire and water). The earliest practical chemists were Arabian, who, around 800 A.D. began by simply categorizing materials (like different materials) and trying to decide if they are the same or not. It’s not so easy; depending on how compressed it is, limestone might look very different, but it always creates fizzing when exposed to acids.

A couple of hundred years later (around 1000 AD) the earliest alchemists seem to have begun. The alchemists followed the teachings of the ancient alchemist philosophers, believing the four elements, and that the sciences involved spirituality as well. The alchemists were active in their laboratory studies, working to perfect certain basic laboratory practices, including mixing, separation, distillation, reflux (heating a solution without loss of volume; it is based on distillation but drips back into the reaction flask) and such.

The beginning of the end for the alchemists is considered to be with the publication of “The Skeptical Alchymist”, by Robert Boyle in 1660. The start of modern chemistry is considered to be the publication of atomic theory by John Dalton in 1808.

Yes, modern chemistry is only about 200 years old; it is younger than America.

There are four components of atomic theory, that largely follow the beliefs if the ancient Atomist philosophers (yes, they were pretty much right). First, all matter is made of individual indestructible particles called “atoms” (Dalton called them “atoms” as a proverbial tip of the hat to the Atomist philosophers). He was largely correct about this; atoms can only be destroyed in high energy physics nuclear reactions. Second, he suggested that two atoms of the same type are indistinguishable. He was largely correct on this; there are atoms of the same type called “isotopes” that are very very similar to each other, but are chemically nearly indistinguishable to the point that most chemists ignore these differences. Third, which is almost an extension of the second, atoms of two different elements are distinguishable. Well, duh, although there are some elements that belong to “families” that behave very similarly. Finally, atoms of two or more different types combine in simple whole-number ratios making “compounds”. This is absolutely true; change the ratio and you change the compound. Water is 2 parts hydrogen to 1 part oxygen, which we need to survive, while two parts hydrogen to two parts oxygen forms hydrogen peroxide, which can kill us. This theory is what all chemistry is still based on even today.

In 1811 (only a few years after Dalton’s law), Avogadro’s law was proposed (that the ratio of the masses were fixed). It took another hundred years, in 1909, until the first estimate of what this number actually is was published (6.02×10^23).

Currently there are 118 elements, but the newer ones aren’t really practical because they don’t last long enough. There are, oh, maybe a hundred or so practical elements. Dmitri Mendeleev introduced the first practical arrangement of the known elements, known today as the “Periodic Table of the Elements” in 1869. Basically, he arranged the elements by mass and realized that the properties of these elements seemed to repeat when they did this. For example, the first column of the periodic table (the columns are called “families” because they have similar properties) all react violently with water.

So there you go; a little bit of history of the humble, in amazingly recent, development of the field of Chemistry. Happy National Mole Day!

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