The Origins of the Periodic Table
Contrary to schoolyard rumors, no one created the periodic table just to torture you—it all started with the elements. As early as 330 BCE, Aristotle created a four-element table: earth, air, fire, and water. (We'd sign up for a test on that periodic table, no problem.) But it wasn't until the late 1700s that Antoine Lavoisier wrote the first list of 33 elements. He classified them as metals and nonmetals, though we now know that some were compounds or mixtures. Other chemists found 63 elements through the mid-1800s, including their properties and compounds, and during that time, scientists also started noticing unexpected patterns in the properties.
For example, Johann Dobereiner discovered that the atomic weight of strontium fell exactly between the weights of calcium and barium, and all three had similar properties. From this, he created the Law of Triads, which said that in triads of elements, the properties of the middle element would be the average of the other two, if you ordered the elements by atomic weight.
When other scientists tested the theory, they basically found that the triads weren't really triads but parts of larger groups. (For instance, fluorine was added to the halogen "triad.") The main drag on their research was inaccurate measuring tools—if you're trying to order the elements by weight to figure out their relationships, it would have helped to know the correct values.
Shoddy measuring tools didn't stop progress, though. Enter French geologist A.E. Beguyer de Chancourtois, who lined up the elements on a cylinder in order of increasing atomic weight. By stacking the closely related elements, he noticed that their properties repeated every seven elements. The chart had one major flaw: it included ions and compounds as well as elements. A year later (in 1864), John Newlands created the Law of Octaves. Newlands noticed the same pattern that de Chancourtois did—repetition within columns. He also arranged the elements in order of atomic weight and observed similarities between the first and ninth elements, third and eleventh, etc. Much like de Chancourtois, Newlands had one major oversight in his table: he didn't leave any spaces for elements that hadn't been discovered yet.
Five years later, we got not one, but the first two, full-fledged periodic tables. Working independently, Lothar Meyer and Dmitri Mendeleev both developed periodic tables. Meyer had published a textbook in 1864 that included an abbreviated version of a periodic table, demonstrating periodic changes in relation to atomic weight. He completed an extended table in 1868 and gave it to a colleague—who obviously took a bit too long to review it. During the review time, Mendeleev's table was published (1869), and Meyer's didn't appear until the next year.
To be fair, Mendeleev's thought process also appears to have been a little bit different than Meyer's. After noticing several patterns, he decided to create a card for each of the 63 known elements that would include the symbol, atomic weight, and chemical and physical properties. He arranged the cards on a table in order of atomic weight and grouped elements with similar properties. The table ended up showing not only group relationships, but vertical, horizontal, and diagonal relationships as well. (Alas, poor Mendeleev came only one vote away from being awarded the 1906 Nobel Prize for his work.) Unlike Meyers, Mendeleev was able to use the gaps in his table to make predictions about yet-to-be-discovered elements, and remarkably, many turned out to be true.
[See Also: Name the Noble Gases in 1 Minute]
This article was written by Liz Hunt and excerpted from the mental_floss book In the Beginning: The Origins of Everything. You can pick up a copy in our store. Also available in our store is the Periodic Table shower curtain.