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The periodic table of elements, in the form introduced by Dmitri Mendeleev, is something that many of us take for granted. But as Philip Ball explains, there are a number of different visualizations making claims for our attention…

The Periodic Table was conceived as a scheme for bringing order to the elements. When there were deemed to be only four of these—the earth, air, fire, and water of the Greek philosopher Empedocles (it was just one of the elemental systems proposed in ancient times, but enjoyed the weighty advocacy of Plato and Aristotle)—things seemed simple enough. But during the Renaissance, natural philosophers were increasingly forced to accept that the metals then known—copper, iron, lead, tin, mercury, silver and gold—were not as interconvertible as the alchemists believed, but seemed to have an elemental primacy about them, too. More and more of these became recognized—zinc, bismuth, cobalt, and others—along with other new elements such as sulfur, phosphorus, carbon, and, in the late eighteenth century, gaseous elements like nitrogen, hydrogen and oxygen. When the French chemist Antoine Lavoisier (who named those latter two) drew up a list of known elements for his seminal textbook Traité élémentaire de chemie in 1789, he counted 33—including light and heat, which he called caloric.

The list didn’t seem to be arbitrary though. In the early nineteenth century, several scientists noted that some elements seemed to come in families, resembling one another in the kinds of reactions they engaged in and the compounds they formed. Some claimed to see triads: the halogens chlorine, bromine and iodine for example, or the reactive metals sodium, potassium (both discovered by English chemist Humphry Davy in 1807) and lithium (identified in 1817). Was there a hidden pattern to the elements?

The Russian chemist Dmitri Mendeleev, working at Saint Petersburg University, is usually credited with discovering that pattern. A Siberian by birth, with Rasputin-like dishevelled hair and an irascible manner, he published his first Periodic Table in 1869. It is “periodic” because, if you list the elements in order of their mass, certain chemical properties seem to recur periodically along the list. The table is produced by folding that linear list so that elements with shared properties sit in vertical columns (although Mendeleev’s first table had them instead in rows, effectively turning today’s table on its side)…

Still, it’s a weird kind of periodicity. At first, chemical properties seemed to recur every eight elements. But in the row that starts with potassium, there’s an interlude of ten metals—the transition metals—and so it continues thereafter, creating a periodicity of 18. And after lanthanum (element 57), chemists discovered a whole series of 14 metallic elements with almost identical properties that have to be squeezed in too—frankly, these elements, called the lanthanides after the first of their ilk, all seem a bit redundant. There’s another block like this after radioactive actinium (element 89), called the actinides. In most Periodic Tables, the lanthanide and actinide blocks are left floating freely underneath so the table doesn’t get stretched beyond the confines of the page. (Some insist that this long-form table is the only proper one.) Why this odd structure?

The answer became clear with the invention of quantum mechanics in the early twentieth century. The chemical properties of New Zealander Ernest Rutherford showed that atoms comprise a central, very dense nucleus with a positive electrical charge, surrounded by enough negatively charged electrons to perfectly balance that charge. Rutherford imagined the electrons orbiting the nucleus like moons, but in the quantum-mechanical description they occupy nebulous, smeared-out clouds called orbitals. Using quantum mechanics to describe the disposition of electrons shows that they are arrayed in shells. The first of these can contain just two electrons—this is the only shell possessed by hydrogen and helium, the two lone elements at the tops of the towers—while the next has eight, and then 18. The shape of the periodic table thus encodes the character of the quantum atom.

All clear? Not quite. Even now, there’s no consensus about how to draw the Periodic Table…

Read on to explore some fascinating alternative depictions: “Picture This: The Periodic Table,” by @philipcball in @PioneerWorks_.

* Bill Bryson, A Short History of Nearly Everything

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As we ruminate on relationships, we might spare a thought for Vladimir Vernadsky; he died on this date in 1945. A Ukrainian mineralogist and geochemist, he is considered one of the founders of geochemistry, biogeochemistry, and radiogeology. He also co-founded and served as the first President of the Ukrainian Academy of Sciences (now National Academy of Sciences of Ukraine).

Vernadsky is probably best remembered for his 1926 book Biosphere, in which he popularized the concepts of the biosphere and the noosphere, arguing (after Eduard Suess) that in the Earth’s development, the noosphere (cognitive life) is the third stage in the earth’s development, after the geosphere (inanimate matter) and the biosphere (biological life). Just as the emergence of life fundamentally transformed the geosphere, the emergence of human cognition will fundamentally transform the biosphere. In this theory, the principles of both life and cognition are essential features of the Earth’s evolution, and must have been implicit in the earth all along (a position Vernadsky held was complementary to Darwin’s theory of evolution). Indeed, within the last 200 years, humanity has been a powerful geologic force, moving more mass upon the earth than has the biosphere.

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