C&EN: IT'S ELEMENTAL: THE PERIODIC TABLE

POTASSIUM

SUSAN R. MORRISSEY, C&EN WASHINGTON

What do you think of when you look at element number 19 on the periodic table? As a chemist, I suppose my head should be filled with images of chemically related things involving potassium, such as zeolite structures being charge-balanced by K⁺, but instead I think of what has to be one of the all-time great pickup lines.

I was doing chemical research at my college during the summer break and decided to attend a gathering at a friend's apartment. It was a small school, so there weren't many students around--just science enthusiasts like myself, those taking summer classes, and a handful of others there for random reasons--but I hoped a lot of people would show up.

As the night got under way, I noticed a not-so-bad-looking guy whom I'd seen around campus. Before long, I found myself face to face with him. He struck up a conversation that included the standard question about why I was on campus and not spending the summer relaxing by a pool somewhere, which is where he'd be if he didn't have to retake a class he'd failed the past semester.

POTASSIUM AT A GLANCE

Name: From the English potash. The symbol for potassium comes from the Latinkalium,alkali.

Atomic mass: 39.10.

History: Isolated in 1807 by Sir Humphry Davy.

Occurrence: The seventh most abundant metal, but it is never found free in nature. Potassium is an essential constituent for plant growth and is found in most soils. It occurs in many minerals mined in Germany, Spain, Canada, the U.S., and Italy.

Appearance: Soft, silvery metal.

Behavior: One of the most reactive and electropositive metals. Apart from lithium, it is the least dense metal known. Potassium oxidizes very rapidly in air and must be stored under argon or under a suitable mineral oil. It reacts with water to form potassium hydroxide, hydrogen gas, and heat, and the heat usually ignites the hydrogen. Potassium and its salts impart a lilac color to flames.

Uses: The metal is rarely used, but its compounds are important components of fertilizers, match heads, glass, soaps, and detergents. The potassium-40 isotope is used to date rocks.

8136element_potassium

GOING APE Bananas provide a great source of potassium--a key mineral for good health.
PHOTODISC

I explained that I was a chemistry major and was taking advantage of a wonderful opportunity to do summer research. Now, usually guys aren't all that interested in chemistry and just find another topic to talk about, but not this one. Instead, he replied, "So, what's your favorite element?"

This would not have struck me as weird if we had both been science majors, but I knew enough about him to make me wonder if he had ever taken a chemistry class. You can imagine my shock and intrigue when I heard the question. I was speechless. I had an affinity for a number of elements, but I hadn't ever really thought about which one element was my favorite.

After some quick thinking, I recall blurting out tin because I was working with organotin halide compounds that summer in the lab. I then became curious to know if he had a favorite element. As it turns out, he did: potassium.

Why potassium, you might ask--well at least I did. It turns out that it's not because of the alkali metal's ability to regulate water balance in the body or its use in fireworks, but simply because he liked bananas, which--as we all know--are full of potassium.

I could appreciate his affection for bananas--after all, they taste great and are good for you. In fact, potassium is an electrolyte mineral essential to maintaining good health. Among its many roles, potassium regulates cellular acid-base and fluid balance, blood pressure, and neuromuscular function.

Potassium deficiency is rare in people who eat a balanced diet because adequate levels of the mineral are found in a variety of foods. For example, meats, poultry, and fish are high in K, as are bananas, potatoes, milk, and orange juice. Carrots, grapefruit, and onions all contain moderate levels of K, while foods such as blueberries, cucumbers, and iceberg lettuce all have low K levels.

But I digress. There is no doubt that potassium is important to good health, but the question that night was whether it was good for the health of my social life. As our conversation continued, I began to wonder if I had misjudged this guy's chemical intellect. Perhaps I should have given him more credit, I thought.

My doubt was short lived. One of the things that I found odd when I first learned about potassium was its chemical symbol, so I thought I would see if he felt the same way. But when I asked him if he also found it odd that potassium's symbol was K, he blew his wise chemical facade.

"K?" he responded, asserting that the symbol was without a doubt P. Needless to say, we spent a good bit of time arguing whether K or P was the correct symbol. He just wasn't buying that the K came from potassium's Latin name, kalium, or that I was a chemistry major who knew my elements. I even went as far as looking through my friend's apartment for a book that had a periodic table in it, but unfortunately she didn't have any science books around.

Days later, I caught up with him at the library and was able to show him a copy of the periodic table, thus proving K was really the correct symbol.

Looking back, my excitement over talking chemistry at a college outing was a bit nerdy, but this guy didn't seem to mind. Although things didn't pan out between us, we had chemistry working for us for at least one evening. I just hope that he still remembers the correct symbol for potassium as well as I remember his pickup line.

Susan Morrissey received her Ph.D. in chemistry from Texas A&M University. She is an associate editor covering government and policy issues for C&EN.

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