PrintThe periodic table classifies the elements according to their electron configuration. The scientist given credit for the modern periodic table is Russian chemist Dmitri Mendeleev. Please watch the following video (4:24) which explains the true genius of what Mendeleev accomplished.
To Watch
The periodic table is instantly recognizable. It's not just in every chemistry lab worldwide, it's found on t-shirts, coffee mugs, and shower curtains. But the periodic table isn't just another trendy icon. It's a massive slab of human genius, up there with the Taj Mahal, the Mona Lisa, and the ice cream sandwich -- and the table's creator, Dmitri Mendeleev, is a bonafide science hall-of-famer. But why? What's so great about him and his table? Is it because he made a comprehensive list of the known elements? Nah, you don't earn a spot in science Valhalla just for making a list. Besides, Mendeleev was far from the first person to do that. Is it because Mendeleev arranged elements with similar properties together? Not really, that had already been done too. So what was Mendeleev's genius?
Let's look at one of the first versions of the periodic table from around 1870. Here we see elements designated by their two-letter symbols arranged in a table. Check out the entry of the third column, fifth row. There's a dash there. From that unassuming placeholder springs the raw brilliance of Mendeleev. That dash is science. By putting that dash there, Dmitri was making a bold statement. He said -- and I'm paraphrasing here -- Y'all haven't discovered this element yet. In the meantime, I'm going to give it a name. It's one step away from aluminum, so we'll call it eka-aluminum, "eka" being Sanskrit for one. Nobody's found eka-aluminum yet, so we don't know anything about it, right? Wrong! Based on where it's located, I can tell you all about it. First of all, an atom of eka-aluminum has an atomic weight of 68, about 68 times heavier than a hydrogen atom. When eka-aluminum is isolated, you'll see it's a solid metal at room temperature. It's shiny, it conducts heat really well, it can be flattened into a sheet, stretched into a wire, but its melting point is low. Like, freakishly low. Oh, and a cubic centimeter of it will weigh six grams.
Mendeleev could predict all of these things simply from where the blank spot was, and his understanding of how the elements surrounding it behave. A few years after this prediction, a French guy named Paul Emile Lecoq de Boisbaudran discovered a new element in ore samples and named it gallium after Gaul, the historical name for France. Gallium is one step away from aluminum on the periodic table. It's eka-aluminum. So were Mendeleev's predictions right? Gallium's atomic weight is 69.72. A cubic centimeter of it weighs 5.9 grams. It's a solid metal at room temperature, but it melts at a paltry 30 degrees Celcius, 85 degrees Fahrenheit. It melts in your mouth and in your hand.
Not only did Mendeleev completely nail gallium, he predicted other elements that were unknown at the time: scandium, germanium, rhenium. The element he called eka-manganese is now called technetium. Technetium is so rare it couldn't be isolated until it was synthesized in a cyclotron in 1937, almost 70 years after Dmitri predicted its existence, 30 years after he died. Dmitri died without a Nobel Prize in 1907, but he wound up receiving a much more exclusive honor. In 1955, scientists at UC Berkeley successfully created 17 atoms of a previously undiscovered element. This element filled an empty spot in the periodic table at number 101, and was officially named Mendelevium in 1963. There have been well over 800 Nobel Prize winners, but only 15 scientists have an element named after them. So the next time you stare at a periodic table, whether it's on the wall of a university classroom or on a five-dollar coffee mug, Dmitri Mendeleev, the architect of the periodic table, will be staring back.
As mentioned in the video the true power of Mendeleev’s periodic table was the predictive ability of his table. This concept is at the heart of science. Scientists cannot just model behavior, but are required to make predictions, which later can be verified or refuted, thus, providing a test for the validity of their model or theories. It is interesting to note that Mendeleev’s work in the 1870s preceded the discovery of the atom which occurred with J.J. Thompson’s discovery of the electron in 1897 and the later work on the nucleus after 1900.
To Read
Now proceed to your e-textbook and finish reading this lesson’s reading assignment (pages 47 to 64 in Chapter 3 of Materials for Today's World, Custom Edition for Penn State University). Please proceed to the next webpage when you have completed this reading assignment.