Metallic personalities

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.