History
Blast from the Past: Periodic Table Style
Get comfortable. Find your favorite blanket and snuggle up in a chair. Relax. We'd tell you to close your eyes too, but that might make this whole reading thing a little difficult. Now picture your chemistry classroom. (If you're not feeling imaginative, just take a look at the picture below.)
A typical chemistry classroom.
You might notice the lab benches lining the classroom, and you can't ignore the safety shower that is legally required to be in every chemistry lab. Now picture the walls. Do you see that unmistakable beacon of chemical knowledge? Yeah, we're talking about the periodic table.
The periodic table we all know (and love).
The periodic table that we all know and love has its origins in the work of Dmitri Mendeleev. Mr. M, as we like to call him, was a nineteenth-century Russian chemistry professor.1 In his time, about 63 elements had been discovered. (Today we are up to 118 elements.) Surprisingly, a lot was known about these elements even back then. We knew their relative masses, chemical reactivity, and some of their physical properties. One very important thing was missing, however…a systematic way of organizing them. Mr. M to the rescue.
Dmitri Ivanovich Mendeleev (1834-1907)
Mendeleev, smarty pants that he was, noticed that certain elements have similar properties. After using some time, effort, and mad puzzle-solving skills, he found that if he listed the elements in order of increasing mass, those similar properties recurred in a regular pattern, a phenomenon he called periodic law. His mind was blown.
During arts and crafts time, Mendeleev organized all of the known elements in a table. First he arranged them from left to right in order of increasing mass. Next he aligned elements with similar properties in the same vertical columns. Since many elements had not yet been discovered, this first table contained tons of gaps. Check out Mr. M's handy work below.
Mendeleev's periodic table from 1871.
These gaps in Mendeleev's periodic table actually allowed him to be somewhat of a wizard. He could predict the discovery of future elements. Move over Harry Potter, we've got a new chosen one in town. For example, Mendeleev predicted the existence of an element he called eka-silicon, which filled the blank space below silicon, in between gallium and arsenic.Oh, Mr. M, how you look not with the eyes but with the mind. In 1886, eka-silicon was discovered by Clemens Winkler. He named this new element germanium, and it had almost exactly the same properties that Mendeleev had predicted.2
Mendeleev's original creation has evolved into the modern periodic table. There are a few changes that have occurred since the nineteenth-century though. In the modern periodic table we're all familiar with, the elements are arranged in order of increasing atomic number rather than increasing relative mass. The modern table also contains more elements than Mendeleev's original table because many more have been discovered since his time. But we won't hold it against him.