In 1869, Mendeleev left empty boxes in his table and described the elements that should fill them. Each box was a public wager.
The question
Did Mendeleev win all his bets?
What you do Press play: the years run from 1869 to 1923, and the boxes he announced fill up, or do not. Then compare what was predicted for germanium with what was measured.
Without JavaScript, here are the animation’s data.
| Box announced | What was found | Year | Wager | Source |
|---|---|---|---|---|
| Eka-aluminium, below aluminium | Gallium, detected by Paul-Émile Lecoq de Boisbaudran in the light it emits | 1875 | won | 1 |
| Eka-boron, below boron | Scandium, found by Lars Fredrik Nilson | 1879 | won | 2 |
| Eka-silicon, below silicon | Germanium, found by Clemens Winkler in a silver ore | 1886 | won | 3 |
| Zirconium’s neighbour | Hafnium, which was not where he expected it: he had not seen the lanthanide family | 1923 | lost | 4 |
| Elements lighter than hydrogen | Nothing: none exist | — | lost | 5 |
| An element for the green line in the Sun’s corona | Nothing: the line came from a very highly ionised iron atom | — | lost | 6 |
| Property | Predicted by Mendeleev | Measured in 1886 | Source |
|---|---|---|---|
| Atomic mass | about 72 | 72.3 | 7 |
| Density (g/cm³) | about 5.5 | 5.47 | 8 |
| Boiling point of the chloride (°C) | about 100, probably lower | 86 | 9 |
| Density of the oxide | about 4.7 | 4.70 | 10 |
The gaps between prediction and measurement are calculated from these figures.
The takeaway A theory convinces when it takes risks: written predictions that can be checked. Mendeleev won three, and lost others.
Photo credits 9
- Crystals of 99.999% pure gallium. foobar (English Wikipedia), CC BY-SA 3.0, source
- Lecoq de Boisbaudran, who discovered gallium, samarium and dysprosium. Unknown author, Public domain, source
- Sublimed dendritic scandium, 99.998% pure, with an argon-arc remelted 1 cm³ scandium cube for comparison. Alchemist-hp (www.pse-mendelejew.de), Free Art License, source
- Lars Fredrik Nilson (1840-1899). Unknown author, Public domain, source
- 12 grams of polycrystalline germanium (2 × 3 cm). Jurii, CC BY 3.0, source
- Clemens Alexander Winkler. Unknown author, Public domain, source
- Facsimile of the periodic table of the elements published by Dmitri Mendeleev in 1869. Dmitri Mendeleev, Public domain, source
- Pure hafnium: a melted piece, an ingot with an oxidised, iridescent surface, and a one-centimetre cube for comparison. Alchemist-hp, Free Art License, source
- The Sun’s corona during the 2008 eclipse. In green, the light given off by very highly ionised iron atoms, at 530.3 nanometres: the ’green line’. NASA (Habbal), Public domain, source
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Sources 10
Lecoq de Boisbaudran, Paul-Émile, “Caractères chimiques et spectroscopiques d’un nouveau métal, le gallium”, Comptes rendus de l’Académie des sciences, t. 81, 1875, p. 493-495, title of the note (p. 493) and additional note (p. 494), session of Monday 20 September 1875.
Caractères chimiques et spectroscopiques d'un nouveau métal, le Gallium, découvert dans une blende de la mine de Pierrefitte, vallée d'Argelès (Pyrénées). […] Les expériences que j'ai exécutées depuis le 29 août me confirment dans la pensée que le corps observé doit être considéré comme un nouvel élément, auquel je propose de donner le nom de Gallium.
Editors’ translation Chemical and spectroscopic characteristics of a new metal, Gallium, discovered in a blende from the Pierrefitte mine, Argelès valley (Pyrenees). […] The experiments I have carried out since 29 August confirm me in the view that the substance observed must be regarded as a new element, to which I propose to give the name Gallium.
Public domain · checked on 24 October 2026
Nilson, Lars Fredrik, “Sur le scandium, élément nouveau”, Comptes rendus de l’Académie des sciences, t. 88, 1879, p. 645-648, note “Sur le scandium, élément nouveau”, last paragraph, p. 648.
Je termine cette Note en exprimant ma reconnaissance à M. Thalén, pour ses recherches spectrales exécutées sur les produits renfermant le scandium. N'ayant encore à ma disposition qu'une quantité très-faible de ce corps, […] je n'aurais pas pu, sans sa coopération puissante, arriver dès aujourd'hui à démontrer l'existence d'un élément nouveau.
Editors’ translation I end this Note by expressing my gratitude to Mr Thalén for the spectral analyses he carried out on the products containing scandium. Having as yet only a very small quantity of this substance at my disposal, […] I could not, without his powerful cooperation, have succeeded as early as today in demonstrating the existence of a new element.
Public domain open the source · checked on 27 October 2026
Winkler, Clemens, “Germanium, Ge, ein neues, nichtmetallisches Element”, Berichte der deutschen chemischen Gesellschaft, vol. 19, 1886, p. 210-211 ; et “Mittheilungen über das Germanium”, Journal für praktische Chemie, vol. 34, 1886, p. 177-229, « Mittheilungen über das Germanium », Journal für praktische Chemie, n. F., vol. 34, 1886, p. 177 (first paragraph), p. 183 and p. 185.
Im Februar dieses Jahres machte ich Mittheilung über die Auffindung eines neuen Elementes im Argyrodit von „Himmelsfürst Fundgrube“ bei Freiberg, doch vermochte ich zunächst nicht viel mehr zu melden, als die zweifellose Thatsache seiner Existenz. […] der Name des neuen Elementes, der Name Germanium, hat das unerwartete Schicksal gehabt, zum Stein des Anstosses zu werden. […] ein bisher nicht vorgekommenes Silbererz aufgefunden, welches A. Weisbach als eine neue Mineralspecies erkannte
Editors’ translation In February of this year I reported the discovery of a new element in the argyrodite of the “Himmelsfürst Fundgrube” mine near Freiberg, but at first I was able to report little more than the undoubted fact of its existence. […] the name of the new element, the name germanium, has met with the unexpected fate of becoming a stumbling block. […] a hitherto unknown silver ore was found, which A. Weisbach recognised as a new mineral species
Public domain open the source · checked on 24 October 2026
Lente, Gábor, “Where Mendeleev was wrong: predicted elements that have never been found”, ChemTexts, vol. 5, art. 17, 2019, abstract, 2nd sentence.
It is argued that most of these instances are connected to a general inability to place the rare earth metals correctly into the system.
Open access open the source · checked on 27 October 2026
Lente, Gábor, “Where Mendeleev was wrong: predicted elements that have never been found”, ChemTexts, vol. 5, art. 17, 2019, abstract, 1st and 3rd sentences (article title: “Where Mendeleev was wrong: predicted elements that have never been found”).
This contribution gives a detailed account of the element predictions Dmitri Ivanovich Mendeleev made after setting up the periodic table of the elements in 1869, with a special focus on those that turned out to be unsuccessful. […] Furthermore, details of conceiving the ideas for two lighter-than-hydrogen elements, newtonium and coronium, are discussed.
Open access open the source · checked on 27 October 2026
Mendeleïev, Dmitri, An Attempt Towards a Chemical Conception of the Ether, trad. George Kamensky, Longmans, Green and Co., Londres, 1904, pp. 25-27 (element y, in the first series of the zero group of the table on p. 26); p. 28 (coronium).
Let us first consider the element in the first series of the zero group. It is designated by y. […] Such an analogue of helium may perhaps be found in coronium, whose spectrum, clearly visible in the solar corona above (that is, further from the sun than) that of hydrogen, is simple like that of helium […] Young and Harkness independently observed the spectrum of this unknown element during the solar eclipse of 1869. It is characterised by a bright-green line […]
Public domain open the source · checked on 27 October 2026
Winkler, Clemens, “Germanium, Ge, ein neues, nichtmetallisches Element”, Berichte der deutschen chemischen Gesellschaft, vol. 19, 1886, p. 210-211 ; et “Mittheilungen über das Germanium”, Journal für praktische Chemie, vol. 34, 1886, p. 177-229, « Mittheilungen über das Germanium », pp. 196-197 (Mendeleev’s prediction quoted) and p. 203 (mean of the measurements).
Sein Atomgewicht wird ungefähr 72, sein specifisches Gewicht 5,5, sein Atomvolumen annähernd 13 sein. […] Mittel 72,32
Editors’ translation Its atomic weight will be about 72, its specific gravity 5.5, its atomic volume approximately 13. […] Mean 72.32
Public domain · checked on 9 September 2026
Winkler, Clemens, “Germanium, Ge, ein neues, nichtmetallisches Element”, Berichte der deutschen chemischen Gesellschaft, vol. 19, 1886, p. 210-211 ; et “Mittheilungen über das Germanium”, Journal für praktische Chemie, vol. 34, 1886, p. 177-229, « Mittheilungen über das Germanium », pp. 196-197 (prediction quoted) and p. 201 (measurement).
Sein Atomgewicht wird ungefähr 72, sein specifisches Gewicht 5,5, sein Atomvolumen annähernd 13 sein. […] Das spec. Gew. bestimmte Herr P. Mann bei 20,4° zu 5,469
Editors’ translation Its atomic weight will be about 72, its specific gravity 5.5, its atomic volume approximately 13. […] Mr P. Mann determined the specific gravity at 20.4° to be 5.469
Public domain · checked on 9 September 2026
Winkler, Clemens, “Germanium, Ge, ein neues, nichtmetallisches Element”, Berichte der deutschen chemischen Gesellschaft, vol. 19, 1886, p. 210-211 ; et “Mittheilungen über das Germanium”, Journal für praktische Chemie, vol. 34, 1886, p. 177-229, “Mittheilungen über das Germanium”, p. 198 (Mendeleev’s prediction quoted) and p. 206 (measurement by Nilson and Pettersson reported by Winkler).
Das Ekasiliciumchlorid EsCl4 wird dagegen eine bei 100° siedende (wahrscheinlich etwas niedriger) flüchtige Flüssigkeit sein […] Die Dampfdichte des bei 86° siedenden Chlorids GeCl4 betrug:
Editors’ translation Ekasilicon chloride EsCl4, on the other hand, will be a volatile liquid boiling at 100° (probably somewhat lower) […] The vapour density of the chloride GeCl4, boiling at 86°, was:
Public domain open the source · checked on 27 October 2026
Winkler, Clemens, “Germanium, Ge, ein neues, nichtmetallisches Element”, Berichte der deutschen chemischen Gesellschaft, vol. 19, 1886, p. 210-211 ; et “Mittheilungen über das Germanium”, Journal für praktische Chemie, vol. 34, 1886, p. 177-229, « Mittheilungen über das Germanium », pp. 196-197 (predictions quoted) and p. 212 (measurement).
Das Ekasilicium mit dem Oxyde EsO2 nimmt die Mittelstelle zwischen Ekaaluminium […] Das specifische Gewicht des Oxydes wird gegen 4,7 sein […] zu 4,703 bestimmt wurde.
Editors’ translation Eka-silicon, with the oxide EsO2, occupies the intermediate position between eka-aluminium […] The specific gravity of the oxide will be about 4.7 […] was determined to be 4.703.
Public domain · checked on 9 September 2026