Germanium Arrived According To Plan

Germanium is a metalloid and thus only a half-metal. Despite this, it was a "planned" element. By planned I mean that its existence was foretold by the father of the periodic table, Russian chemist Dmitri Mendeleev.

Mendeleev was not the first to bring rhyme and reason to the elements--first came columns--Döbereiner's triads, and later rows--Newlands' Law of Octaves. But Mendeleev properly put together the whole kahuna, or at least what was known at the time. More importantly, he correctly predicted elements. Here's what he knew and what he knew must exist in 1871:

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It's hard to see, but Mendeleev left a blank: "--  = 72 " in Group IV.  He called the unknown element eka-Silicon meaning one below Silicon. Eka-Silcon was discovered in 1886 and had an atomic mass of 72.6 amu. Van der Krogt tells the story of naming Germanium here, along with some Roman history.

Mendeleev also predicted the existence of eka-Aluminum and estimated its mass as 68.  The element was discovered and named Gallium in 1875 and had an atomic mass of 69.7 amu. The agreement between theory and experiment was almost as astonishing as Bode's Law. But Mendeleev's table survived.

Past and Present: Now The Twain Shall Meet

Now, if I wanted to be one of those ponderous scientific people, and `let on' to prove what had occurred in the remote past by what had occurred in a given time in the recent past, or what will occur in the far future by what has occurred in late years, what an opportunity is here! Geology never had such a chance, nor such exact data to argue from! Nor `development of species', either! Glacial epochs are great things, but they are vague--vague. Please observe. In the space of one hundred and seventy-six years the Lower Mississippi has shortened itself two hundred and forty-two miles. This is an average of a trifle over one mile and a third per year. Therefore, any calm person, who is not blind or idiotic, can see that in the Old Oolitic Silurian Period, just a million years ago next November, the Lower Mississippi River was upward of one million three hundred thousand miles long, and stuck out over the Gulf of Mexico like a fishing-rod. And by the same token any person can see that seven hundred and forty-two years from now the Lower Mississippi will be only a mile and three-quarters long, and Cairo and New Orleans will have joined their streets together, and be plodding comfortably along under a single mayor and a mutual board of aldermen. There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.

~Mark Twain, The Atlantic Monthly, 36, 193 (1875)

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Mark Twain's autobiography is finally coming out after 100 years of waiting: link.  I'm expecting the unexpected, based on conjecture.