Northeastern University

Metallic personalities

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Image via Thinkstock.

Image via Thinkstock.

Civil and environmental engineering professor Philip Larese-Casanova has had a life-long love affair with metals. In his work in aquatic environmental chemistry, he looks at how metallic pollutants transform and behave in freshwater systems.

“I just had an interest in the metals,” he told me in an interview last month. “Maybe it’s because I see so many different personalities in them when I look at the periodic table.” I almost fainted like a Jane Austen character when he said that.

Larese-Casanova’s passion for chemistry transcends the calm patience with which he discusses the complex subject. But when I asked what exactly he meant by a metal’s “personality,” Larese-Casanova said: “It’s kind of like asking me, how did I fall in love with my wife ? It’s hard to verbalize a multifaceted passion concisely.”

He pulled out a picture of the periodic table to try and explain it:

“We can tolerate, for example, sulfate at low concentrations. But drop one period down and we get to selenium. Selenate is generally toxic,” he said. “So you make one small change, move down or across the periodic table and you can get to an element with completely different reactivities, toxicities, and chemical behaviors.”

The word “periodic” is important here too, as chemical trends cycle from one row to the next. For example, each row ends with a so-called “noble” gas, which doesn’t react with anything else. As Larese-Casanova mentioned, the elements in any column have similar chemical properties. Sitting directly above it in the column (or “group”), phosphorous reacts with other elements in a similar way as arsenic.

The periodic table of the elements has a rich history, beginning with Antoine Lavoisier who arranged the then-known elements into groups of gases, metals, nonmetals, and earths, and culminating with Dmitri Mendeleev who found that arranging the elements based on their atomic weights would mystifyingly group them in the same way Lavosier had. Eclectic Artwork by Other Metro Sideshow Sign Company.

The periodic table of the elements has a rich history, beginning with Antoine Lavoisier who arranged the then-known elements into groups of gases, metals, nonmetals, and earths, and culminating with Dmitri Mendeleev who found that arranging the elements based on their atomic weights would mystifyingly group them in the same way Lavosier had. Eclectic Artwork by Other Metro Sideshow Sign Company.

Just like two notes on a piano separated by a single octave, these two elements will share similar qualities. Whereas a low C will sound a little deeper than middle C, arsenic share some of the chemical “qualities” of phosphorous. They’re personalities are shadows of each other, like sisters separated by a dozen years in age.

But despite these similarities, phosphorous is a key element in the DNA of all living organisms, whereas arsenic is toxic to nearly all animals (it used to be an ingredient in rat poison!).

This is the beauty of the periodic table, and it helps organize the beauty that Larese-Casanova sees in the metals. While organic compounds are all variations on a theme (they all contain carbon), metallic pollutants are varied and nuanced, predictable and surprising, all at once.


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