Periodic table, now 150 years old, evolves and ages gracefully

There are only a few developments that have organized the way we see the world. There is the classification system of the life sciences, which separated the natural world into kingdoms. There is the Constitution of the United States, which created a delicate system of checks and balances. There is double-entry accounting, which made modern bookkeeping possible and sometimes is credited with giving flight to capitalism. There is the baseball rulebook, which sets forth the infield-fly rule.

And there is the Periodic Table of the Elements.

It almost certainly has escaped your notice, but this month is the 150th anniversary of this key to how the known world (and beyond) is constructed. It has many progenitors, but the principal one is a Russian chemist named Dmitri Mendeleyev, who had a prodigious Old Testament beard, who was shaped by the liberal notions that were in the air of Tsarist Russia in the years between the Decembrist uprising of 1825 and the assassination of Alexander II in 1881, and who was energized by a conference of chemists in the southern German town of Karlsruhe two months before the election of Abraham Lincoln. In March 1869 he crafted a graphic tool that, as Paul Strathern explains in his landmark 2001 “Mendeleyev's Dream,” performed the astonishing achievement of having “classified the building blocks of the universe.”

The Periodic Table was set out by Mendeleyev before the discovery of electrons, so the irony of this tabular display of noble gases and ignoble substances is that a table based on atomic weights could predict interactions between elements even before the discovery of the structure of the atom. That was either a stroke of luck, a stroke of genius -- or, perhaps antithetical to the entire ethos of science, a stroke of providence.

The bane of high-school chemistry students, the Periodic Table is remarkable for predicting elements that would in time fill in its own gaps -- almost like a jigsaw puzzle whose missing pieces would eventually be discovered in the box or on the floor. It is even more impressive because jigsaw puzzles come with an image of how to fill in the blanks, while the Periodic Table had no such assistance.

“In the history of science, there have been few original principles that have proven to be so enduring and powerful for scientists and students alike,” said Christopher J. Phillips, a Carnegie Mellon University expert on the history of science. “It's prompted research into dozens of new substances and new arenas of research into the nature of matter.”

The table -- which shows there are patterns in nature just as there are in human affairs -- moves left to right on the basis of how reactive each element is. Everything under Helium, for example, is like Helium in its structure, and everything under Carbon is like Carbon, possessing similar properties of combining with other elements.

In the search for new elements, scientists have acquired new understandings of what constitutes matter. The radioactive elements, unknown to Mendeleyev, became central to energy, warfare and medicine.

And since the 100th anniversary of the table -- in large measure due to the work of another Russian scientist, the 85-year-old Yuri Oganessian -- nine new elements, including the five heaviest ones, have been added to the table, bringing the number of elements to 118, the last one aptly called Oganesson and designated with the chemical symbol Og. Well before the table -- which began in Mendeleyev's time with 61 elements and moved to 85 in the early 20th century, but now is seven rows deep -- reaches its 200th anniversary, it likely will have an eighth row. Who says there is nothing new under the sun?

These high-number elements won't actually be new but instead simply substances scientists haven't discovered yet or, in the case of 24 of them already identified, artificially created -- the physical-science analogue of the aphorism often attributed to the Irish poet William Butler Yeats: “There are no strangers here, only friends you haven't met yet.”

In the year 1869 -- remembered mostly for the opening of the Suez Canal and for the completion of the Transcontinental Railroad in Utah, two achievements that tied the world more tightly together rather than separating its elements did -- Mendeleyev held the position of professor of chemistry at St. Petersburg University. There he faced the challenge of teaching a required course in inorganic chemistry. The most useful instruction books were badly translated European texts, so he vowed to write his own version. Halfway through, he faced a scientific challenge:

“I had to set up simple bodies in some kind of system so that their distribution was not governed by accidents, as if by instinctive guesses, but by some definite exact principle.”

Indeed, modern chemistry would not be possible without the Periodic Table, as much a roadmap to the far reaches of the universe as it is a gazetteer to the known world. As a result, we remember Mendeleyev as one of the great mapmakers of all time, the laboratory version of Gerardus Mercator, whose landmark 1569 cylindrical projection laid out the known and unknown worlds for others to explore -- or as the scientific version of John Milton, who in Line 26 of his classic “Paradise Lost” set out to “justify the ways of God to men.” Mendeleyev explained the ways of the universe to us all.