By Ron B. Davis Jr., Georgetown University
It might seem hard to imagine, but, late in his career, the great Dmitri Mendeleev had a lot of difficulty with the top left corner of the periodic table. In fact, some twenty years after proposing the table that would secure his scientific legacy forever, Mendeleev himself offered not one, but two predictions that ultimately proved to be false.
The Element Coronium
In the 1890s, Sir William Ramsay isolated and correctly identified the elements helium, neon, argon, xenon, and krypton—all within just a few years. But there was an unresolved issue haunting the noble gases. Astronomers identified a green emission line in the sun’s chromosphere that didn’t seem to belong to any known element. Many believed that this line was produced by an element even lighter than helium—an element that many called coronium.
If there was indeed another element waiting to be discovered, Dmitri Mendeleev knew it had to have a home in his periodic system, and he thought he had just the spot!
Coronium on the Periodic Table
To visualize where Mendeleev thought coronium might belong on the table, let’s consider the modern periodic table.
Mendeleev has a few bonus elements, like polonium, bismuth, and astatine, and the benefit of the doubt for gallium and germanium. But these groups in Mendeleev’s table were numbered one through seven, and those groups were set apart from one another, in part, because of their valence, because of the way that these elements interacted with oxygen. As we move from left to right across Mendeleev’s table, the amount of oxygen, the ratio of oxygen in common compounds, of these compounds, is increasing.
And so when it came to placing the noble gases in the table, if we put them where we normally see them today, on the right hand side of the table, those would constitute a group eight. Now, Mendeleev already had plans for group eight; that’s where he kept many of those, sort of, overflow transition metals, like iron, cobalt and nickel. So instead, he thought of the noble gases in a different way. What if there were a group that didn’t combine with oxygen at all? Meaning, it had a valence of zero. What if there were a group zero in the periodic table? Well, that would have two important impacts on the shape of the table.
First, of course, the noble gases would be in group zero because they don’t combine with oxygen, placing them on the left side of the table. But then the ordering is off. The elements are no longer arranged by increasing atomic number, or atomic mass. And in order to correct this, we need to slide this group down by one period. And in doing so, we create an empty cell just to the left of hydrogen. Mendeleev wondered, could this be the home for coronium?
Only in the 1930s would it eventually be demonstrated that this mystery line in the sun’s corona spectrum was actually due to iron, in an exotic ion so rare that it had never been observed on Earth, and its existence in the sun’s chromosphere remains unexplained even today.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
Luminiferous Ether
Mendeleev’s second mistake, also at the top of the table, can be traced back to the 1870s, when he scribbled a few notes into one of his own tables in his notebook. At the top of that table, he noted, “the ether is lighter than the others by a million times”.
Mendeleev wasn’t referring to the ordinary chemical substance we call ether today. Instead, he was referring to the so-called ‘luminiferous ether’—a material hypothesized to serve as a medium distributed throughout the universe for light to move through as a wave, much the way an ocean wave moves through water.
In Mendeleev’s mind, if the ether existed at all, then it had to be made of something! And if it had evaded detection for so long, it was probably something very small and inert. And the only place he could imagine this postulated form of matter might belong in his system?
Of course—above coronium, in a hypothetical row zero of the table.
Ultimately, however, there was never any evidence found for the ether, and the one-two punch of the Michelson-Morley experiment in 1887 and Einstein’s special relativity theory in 1905. Ether simply didn’t exist. There would be no row zero for the periodic table.
Mendeleev’s Legacy
Mendeleev got himself in trouble with these later predictions because what he tried to extrapolate, he had been filling spaces within the table that were surrounded on two or three sides by known elements, beyond the boundaries of his table. By contrast, his successful predictions had been based on interpolation—filling spaces within the table that were surrounded on two or three sides by known values of known elements.
In spite of these two failed predictions, Mendeleev’s legacy remains that of a chemist whose ingenuity and unfailing belief in a periodic system for the ingredients of the universe catapulted our understanding of the elements into the modern age of chemistry.
Common Questions about Dmitri Mendeleev’s Two False Predictions
Astronomers identified a green emission line in sun’s chromosphere that didn’t seem to belong to any known element. Many believed that this line was produced by an element even lighter than helium—an element that many called coronium.
According to Mendeleev, ‘luminiferous ether’ was a material hypothesized to serve as a medium distributed throughout the universe for light to move through as a wave, much the way an ocean wave moves through water.
Mendeleev’s legacy is that of a chemist whose ingenuity and unfailing belief in a periodic system for the ingredients of the universe catapulted our understanding of the elements into the modern age of chemistry.
