All Thinkers

Dmitri Mendeleev

Dmitri Ivanovich Mendeleev (1834-1907) was a Russian chemist who devised the periodic table of the elements, one of the most important organising schemes in the history of science. He was born in Tobolsk, Siberia, the youngest of what may have been as many as seventeen children. His father, a teacher of philosophy and literature, went blind and then died when Dmitri was still young; his mother kept the family going by running a glass factory. When the factory burned down, she travelled more than two thousand kilometres by horse and cart to take her gifted youngest son to St Petersburg, where she eventually placed him in what became his university. He completed his studies there and went on to postgraduate research in Heidelberg and Paris before returning to teach in St Petersburg. In 1869, while preparing a chemistry textbook, he arranged the known chemical elements in order of atomic weight and noticed that their properties repeated at regular intervals. He published his first periodic table that year. The table left gaps for elements he predicted would be discovered, with detailed forecasts of their properties; when gallium, scandium, and germanium were found in the following decades and matched his predictions, the table's power became undeniable. Mendeleev was also a practical scientist who worked on Russian oil production, agriculture, metrology, and economics. He never received the Nobel Prize, despite being nominated. He died in St Petersburg in 1907.

Origin
Russia
Lifespan
1834-1907
Era
19th century
Subjects
Chemistry Periodic Table Elements Russian Science Scientific Method
Skills
Scientific Thinking Critical Thinking Research Skills Cultural Heritage And Identity Creative Expression
Why They Matter

Mendeleev matters because he found a single ordering that makes sense of all the chemical elements and used it to predict the existence and properties of elements that had not yet been discovered. Before Mendeleev, chemists knew about sixty or so elements. They had noticed that some of these elements resembled each other — lithium, sodium, and potassium were similar soft, reactive metals; chlorine, bromine, and iodine were similar corrosive non-metals — but no one had been able to fit all the similarities into one coherent scheme. Several chemists had attempted partial arrangements in the years before 1869. Mendeleev's arrangement was the one that worked. He ordered the elements by atomic weight and noticed that their chemical properties repeated periodically as the weight increased. His crucial insight was to leave gaps in the table where he believed undiscovered elements should fit, rather than squeezing the known elements into a complete but false pattern. He predicted the atomic weights, densities, melting points, and chemical behaviour of these missing elements with startling accuracy. When the predictions came true, the periodic table became a fact of chemistry rather than one hypothesis among many. It has remained the basic organising chart of chemistry ever since, and later developments — the discovery of noble gases, the understanding of atomic number and electron shells, the synthesis of new elements — have extended rather than overturned it. Every chemistry classroom in the world today has a version of Mendeleev's chart on its wall.

Key Ideas
1
The elements arrange themselves in a pattern
Mendeleev's central discovery was that if you list the chemical elements in order of their atomic weight, their properties repeat at regular intervals. After a light reactive metal like lithium, a few elements later you get sodium, which behaves very similarly. A few after that you get potassium, again similar. The same pattern holds across several families of elements. This repeating, or periodic, behaviour is not an accident. It reflects something real about how the elements are built. Mendeleev could not yet explain why the pattern existed — that would wait for the discovery of atomic structure decades later — but he could see that it did exist, and he built his table to display it.
2
Leaving gaps for what has not yet been found
When Mendeleev drew up his table, some of the known elements did not quite fit into the pattern he was building. Rather than forcing them in or abandoning the pattern, he left empty spaces where no element was yet known. He was effectively betting that new elements would be discovered that would fit these gaps. This was a bold thing to do. Other chemists had the same information and did not leave gaps; they produced neater but less predictive tables. Mendeleev's willingness to leave blank space is a good example of a scientific habit: trusting a pattern enough to predict what is missing, rather than fudging the data to cover all available cases.
3
Predictions that came true
Mendeleev predicted that elements would be found to fill three specific gaps in his table. He gave them temporary names — eka-aluminium, eka-boron, and eka-silicon — and predicted their atomic weights, densities, and chemical behaviour. In 1875 a French chemist discovered gallium, which matched the eka-aluminium prediction closely. Scandium was found in 1879, matching eka-boron. Germanium was found in 1886, matching eka-silicon almost exactly. These confirmations turned the periodic table from an interesting idea into one of the most powerful tools in chemistry. A theory that predicts specific facts that later turn out to be true has passed a difficult test that theories invented to fit known facts have not.
Key Quotations
"The elements, if arranged according to their atomic weights, exhibit an evident periodicity of properties."
— On the Relationship of the Properties of the Elements to Their Atomic Weights, 1869
This is the opening statement of Mendeleev's principle. He is claiming that arranging the elements by atomic weight reveals a pattern — their properties repeat at regular intervals. The word evident matters. He is saying that the pattern is not something imposed on the elements but something that shows itself once they are arranged correctly. This distinction between finding a real pattern in the data and inventing one that fits is at the heart of scientific work, and Mendeleev's periodic law is one of the clearest historical examples of the former.
"There is nothing in this world that I fear to say."
— Reported remark, 1890s
Mendeleev was known for outspokenness on political and social questions as well as scientific ones. He resigned from his university chair in 1890 after delivering a student petition to the tsarist authorities. He wrote openly about problems in Russian industry and education. The remark captures a personality that matched the boldness of leaving gaps in the periodic table: a willingness to say what he thought to be true even when it was uncomfortable. The same intellectual courage runs through his scientific work and his public positions. He did not treat the two as separate.
Using This Thinker in the Classroom
Scientific Thinking When introducing what a scientific classification looks like
How to introduce
Show students the periodic table on the wall. Ask: what do you notice about it? Most will see it as a messy chart of boxes. Introduce the idea that every element with the same column has similar chemical behaviour — the elements on the far left are soft reactive metals; the elements on the far right are unreactive gases. Show how the columns group elements that behave alike. Introduce Mendeleev: this chart did not always exist, and when he proposed it in 1869 he left gaps for elements no one had yet found. Discuss what it takes to make a good classification of anything — not just making things fit, but getting them to fit for reasons that reveal underlying structure.
Scientific Thinking When teaching the value of predictions in science
How to introduce
Tell students the story of Mendeleev's gaps: he left three empty spaces in his table and predicted the properties of the elements that would fill them. Over the following seventeen years, all three predictions came true. Ask students: why does this matter? Could Mendeleev have explained away discrepancies and filled the gaps with existing elements? What is the difference between a theory that fits what you already know and a theory that predicts things you do not yet know? Connect to the broader skill of asking, when you meet a new theory, what does it predict that could fail? A theory that predicts nothing specific cannot really be tested.
Further Reading

For a short accessible introduction: Paul Strathern's Mendeleyev's Dream (2000, Hamish Hamilton) tells the broader story of the search for the elements with Mendeleev as its central figure. Eric Scerri's A Very Short Introduction to the Periodic Table (2011, Oxford University Press) is concise and reliable. The Science Museum in London and the Smithsonian in Washington both maintain online resources on the periodic table's history.

Key Ideas
1
The textbook that started it
Mendeleev did not discover the periodic table while looking for a great principle of chemistry. He discovered it while trying to write a good chemistry textbook. He was teaching at the University of St Petersburg and had been frustrated that no single Russian textbook covered the subject well. He began writing his own, and as he worked his way through the elements he tried to find a natural order for presenting them. The search for a teaching order led him to the underlying pattern. This is worth pausing on. Some of the most important scientific insights have come from the practical demands of teaching rather than from heroic isolated research. Trying to explain something to beginners often reveals what one does not yet understand oneself.
2
Atomic weight and the limits of his ordering
Mendeleev ordered the elements by atomic weight — the average mass of an atom of each element. This worked remarkably well, but there were a few places where it produced the wrong answer. Tellurium is heavier than iodine, but iodine clearly belongs in the family of elements where tellurium would sit if ordered strictly by weight. Mendeleev swapped the two, trusting the chemistry over the measured weight. He turned out to be correct: later work showed that the true ordering principle was not atomic weight but atomic number, the number of protons in the nucleus. Iodine's atomic number is higher than tellurium's even though its atomic weight is lower. Mendeleev could not have known this, but his trust in the chemistry pointed to what atomic number would later confirm.
3
Other contributions: oil, metrology, education
Mendeleev is remembered mainly for the periodic table, but he worked across a wide range of practical and scientific projects. He investigated the Russian petroleum industry and wrote influential reports on how it should be developed. He became head of the Russian bureau of weights and measures and carried out careful work on standardising scientific measurement. He wrote on agriculture, industry, and economic policy. He taught at several institutions and supervised many students. The picture of the one-idea scientific hero is often misleading; Mendeleev was a working scientist whose output covered much more than his most famous single contribution. Understanding this resists the common narrowing of historical figures to the one thing they are remembered for.
Key Quotations
"Having given much time and thought to the fundamental problems of chemistry, I propose in this work to lay before my readers those wider generalisations which, in my opinion, best serve for the embodiment of the various information at present accumulated."
— Preface to The Principles of Chemistry, 1869
Mendeleev is writing the preface to his chemistry textbook, the book whose preparation led him to the periodic table. He is describing what he is trying to do: take the accumulated information about chemistry and find the wider generalisations that organise it. The remark captures a serious view of what a textbook is for. A good textbook does not simply list what is known; it shows how what is known fits together. The search for fitting-together is what led Mendeleev to his discovery. The ambition to find organising principles, rather than merely to catalogue facts, is one of the engines of scientific progress.
"It is the function of science to discover the existence of a general reign of order in nature and to find the causes governing this order."
— Lecture, late career
Mendeleev is stating a general view of what science is for. He thinks nature is orderly — not chaotic or random — and that the task of science is to find that order and work out what produces it. This view was widely held in the nineteenth century and remains a working assumption of most scientific practice. It is not a trivial assumption. The alternative, that nature is fundamentally disorderly or unknowable, would produce a very different attitude toward experiment and theory. Mendeleev's own work is an argument for the orderly view: the periodic table shows that even the sixty or more chemical elements, which look miscellaneous, form a strict pattern.
Using This Thinker in the Classroom
Critical Thinking When examining how scientists decide when to trust a pattern
How to introduce
Introduce Mendeleev's decision to swap tellurium and iodine in his table, even though the atomic weights suggested the opposite order. He trusted the chemistry — the fact that iodine clearly belonged with bromine and chlorine — over the measured weights. He turned out to be right, though the explanation (atomic number rather than weight) came later. Ask students: when should a scientist trust a pattern against the data, and when should the data override the pattern? Discuss the judgment involved. There is no rule that always gives the right answer. What matters is being honest about what you are doing and willing to be proved wrong.
Research Skills When examining how teaching and research feed each other
How to introduce
Tell students that Mendeleev discovered the periodic table while preparing a textbook for students. He was trying to find a good order in which to present the elements to beginners, and the search for a teaching order revealed an underlying scientific pattern. Ask: what does this suggest about the relationship between teaching and research? Discuss the idea that trying to explain something clearly forces you to understand it properly. Many students have had the experience of realising they did not fully understand something until they tried to explain it to someone else. Connect to the broader skill of using explanation as a tool for understanding, not only as a tool for communication.
Cultural Heritage and Identity When examining scientific work outside the usual European centres
How to introduce
Introduce Mendeleev's biography: born in Siberia, brought to St Petersburg by a remarkable mother after the family factory burned down. Ask students: does it matter where major scientific work is done? What does it require for a country not in the traditional European centres of science to produce a first-rank scientific contribution? Discuss the combination of factors: a strong university, international travel for Mendeleev's postgraduate study, communication with the wider scientific community. Connect to broader questions about how scientific capacity is built across different regions and how contributions from outside the usual centres have sometimes been undervalued.
Further Reading

Michael Gordin's A Well-Ordered Thing

Dmitrii Mendeleev and the Shadow of the Periodic Table (2004, Basic Books) is the standard modern scholarly biography in English, readable and authoritative.

Eric Scerri's The Periodic Table

Its Story and Its Significance (2019, Oxford University Press) is the fullest treatment of the history and philosophy of the table. Bernadette Bensaude-Vincent has written important work on the history of chemistry that places Mendeleev in his broader context.

Key Ideas
1
The missing Nobel Prize
Mendeleev was nominated for the Nobel Prize in Chemistry but never received it. The decisive vote came in 1906, a year before his death; by one vote, the prize went to Henri Moissan for his isolation of fluorine and his electric furnace work. The backstage story involves personal disagreements within the Nobel committee, including objections from Svante Arrhenius, whose own theories Mendeleev had opposed. This is a reminder that scientific recognition is made by committees of human beings with histories, preferences, and sometimes grudges. The periodic table was already thirty-seven years old and had been triumphantly confirmed by several element discoveries. Its creator's failure to receive the most famous chemistry prize is evidence that prize decisions are fallible, and that a scientific legacy does not depend on the medals awarded during a lifetime.
2
The development of periodic law before Mendeleev
Mendeleev did not work from nothing. In 1864 the English chemist John Newlands had proposed a law of octaves, noting that chemical properties seemed to repeat every eighth element. The German chemist Lothar Meyer produced arrangements similar to Mendeleev's in the same years, and a few others had made partial attempts. What distinguished Mendeleev was the boldness of leaving gaps, the specificity of his predictions about missing elements, and the sustained development of the idea across the following decades. Recognising his predecessors does not diminish him; it places him in a scientific conversation rather than treating him as a lone genius. Most major scientific ideas have this shape: a cluster of attempts, followed by the one that succeeds, which later gets told as a story of individual discovery.
3
What the table has and has not been extended to do
Since Mendeleev's original publication in 1869, the periodic table has been extended in ways he did not anticipate. Noble gases (helium, neon, argon, and so on) were unknown in his time; their discovery required adding a whole new column to the table, and they now fit as one of its most regular families. The discovery of atomic structure explained why the pattern exists: electron shells fill in a way that produces recurring chemical behaviour. Transuranium elements — those heavier than uranium — have been synthesised in laboratories, extending the table well beyond the elements found in nature. None of these developments has overturned Mendeleev's framework; they have deepened and extended it. This is one mark of a successful scientific idea: it survives and accommodates new discoveries rather than collapsing under them.
Key Quotations
"I had a dream. I saw a table where all the elements fell into place as required."
— Reported remark, attributed late in his career
Mendeleev sometimes told this story about how the periodic table came to him. The attribution is not fully reliable — the dream story appears in later recollections and may have been polished with telling. Mendeleev himself said in other places that the arrangement came from patient work over years, not from a single flash of inspiration. Even if he did have such a dream, it would have come after months of thinking about the problem, not from nowhere. The story is worth knowing because it is often repeated, and because comparing it with Mendeleev's other accounts shows how scientific discoveries can get retold in romantic forms that simplify the actual work.
"Having no preconceived ideas, I have set myself the task of comparing the properties and atomic weights of the elements."
— On the Relationship of the Properties of the Elements, 1869
Mendeleev describes his method as starting without preconceived ideas and letting the comparison of properties and weights reveal whatever pattern was there. This is a claim he and many later scientists would want to make. It is probably too strong. No one looks at the elements without some prior ideas about what similarities to notice and what to ignore. Mendeleev had absorbed years of chemical training before he began arranging his table. But the underlying point is real: he was trying to follow where the data led rather than to fit the data into a scheme he had decided on in advance. The difference between those two approaches is often what separates successful scientific work from wasted effort.
Using This Thinker in the Classroom
Scientific Thinking When discussing how scientific theories survive new discoveries
How to introduce
Present the history of the periodic table after Mendeleev. Noble gases — a whole new family of elements — were discovered in the 1890s and needed a new column. Atomic structure was understood in the twentieth century and showed why the table works. Transuranium elements have been synthesised in laboratories. Ask students: did these discoveries overturn Mendeleev's table or extend it? Discuss the idea that successful scientific theories are often extended and deepened rather than replaced. Compare with cases where theories have been overturned entirely. What is the difference between a theory that accommodates new findings and one that breaks under them?
Critical Thinking When examining the role of prizes and recognition in science
How to introduce
Tell students that Mendeleev was nominated for the Nobel Prize in Chemistry but lost by one vote in 1906, a year before his death, partly because of a personal disagreement on the committee. Ask: does the absence of a Nobel Prize change how we should assess him? Discuss the broader question of how scientific recognition is made by human committees with biases, rivalries, and histories. Consider other cases: Rosalind Franklin and the DNA Nobel, which she could not receive because she had died. Discuss what is and is not captured by prize lists, and how to think about scientific legacy more carefully than prize counts allow.
Common Misconceptions
Common misconception

Mendeleev invented the periodic table from nothing.

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What to teach instead

Several chemists had proposed partial arrangements before Mendeleev, notably John Newlands in England with his law of octaves and Lothar Meyer in Germany. Mendeleev was the one whose table worked, whose predictions succeeded, and who sustained and defended the idea most effectively over decades. Recognising his predecessors does not diminish his achievement; it places him in the actual scientific context of the late 1860s, in which the problem of ordering the elements was being attacked by several people simultaneously. The solo inventor image is appealing but inaccurate. It also obscures how science usually works: a common problem being attacked by several people, with one solution eventually winning.

Common misconception

The periodic table came to Mendeleev in a single dream.

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What to teach instead

The dream story is often told, based on some of Mendeleev's own later recollections. It may have a grain of truth — he may have had a vivid dream that helped consolidate what he was working on. But it cannot be the whole story. Mendeleev had spent years studying the elements, had been working on his textbook, and was actively trying to find a good ordering. If a dream played any role, it came after extensive preparation, not from nowhere. The dream version simplifies a long process into a single moment and feeds a misleading picture of how scientific discovery usually works. Most breakthroughs come from sustained work, with sudden moments of clarity at the end rather than at the beginning.

Common misconception

The modern periodic table is ordered by atomic weight, as Mendeleev intended.

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What to teach instead

The modern periodic table is ordered by atomic number — the number of protons in an atom's nucleus — not by atomic weight. For most elements this gives the same order as atomic weight would, which is why Mendeleev's table worked. But there are places where the two orderings disagree, and in those places atomic number is correct. Mendeleev recognised the discrepancies and swapped some elements on the basis of their chemistry, anticipating the correct ordering without knowing its cause. The discovery of atomic number by Henry Moseley in 1913 provided the explanation. Calling the modern table Mendeleev's table is accurate in spirit but slightly wrong in detail.

Common misconception

Mendeleev was only a chemist and had no interests outside chemistry.

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What to teach instead

Mendeleev worked across an unusually wide range of subjects. He wrote on the Russian petroleum industry, on agriculture, on metrology and weights and measures, on economics, on education, and on social questions. He resigned from his university chair in 1890 to protest the government's treatment of student protests. The image of him as a specialist chemist alone misses much of what he did. Recovering his full range is not just biographical completeness; it corrects a general tendency to reduce historical figures to their single most famous contribution, which often obscures the working life that made the contribution possible.

Intellectual Connections
Anticipates
Marie Curie
Mendeleev's periodic table provided the framework within which Curie's later discovery of radium and polonium would be understood. Curie's elements took their places in the table; their properties fit the patterns Mendeleev had identified. The connection is not direct — Mendeleev did not anticipate radioactivity — but the periodic ordering made it possible for the new elements to be located and understood within existing chemical knowledge. Reading them together shows how a successful framework provides the conditions under which later discoveries can be recognised as discoveries rather than anomalies.
Complements
Charles Darwin
Mendeleev and Darwin are two of the great nineteenth-century scientists whose work consisted of finding a unifying order beneath what looked like miscellaneous diversity. Darwin saw that the many species of living things are connected by descent and modification; Mendeleev saw that the many chemical elements are connected by periodic structure. Both arrived at their discoveries by patient, sustained attention to specific details across years. Both faced the problem of explaining why the order they had found existed — a problem that required later developments (genetics for Darwin, atomic theory for Mendeleev) to solve. Reading them together shows how organising insights can transform a field even before the underlying causes are known.
In Dialogue With
Thomas Kuhn
Kuhn's account of how scientific paradigms work — periods of normal science organised by a framework, punctuated by revolutionary shifts — fits the history of chemistry before and after Mendeleev. Before 1869 chemists were working without a stable framework for ordering the elements. Mendeleev's table provided one, and chemistry settled into productive normal science within it. Later developments extended rather than overturned his scheme. Reading Mendeleev's case through Kuhn's framework helps clarify what kind of scientific event his periodic table was: not a refutation of earlier chemistry but the establishment of a framework chemistry had lacked.
Complements
Mary Anning
Mendeleev and Anning, near contemporaries, both contributed to the nineteenth-century scientific project of finding patterns beneath apparent miscellaneity. Anning's fossils helped establish that the history of life had a structure that could be traced; Mendeleev's table established that the diversity of chemical elements had an underlying order. The fields differ, and their institutional positions were very different — Mendeleev held a university chair, Anning was a working-class fossil collector — but the intellectual project of each was to find ordering principles in apparently unordered data. Reading them together shows how widely this search shaped nineteenth-century science.
In Dialogue With
Ada Lovelace
Lovelace argued that mathematical operations have their own abstract structure, independent of what they are applied to. Mendeleev's periodic law operates at a similar level. The periodicity he discovered is a structural feature of the elements, not of any particular chemical substance. Both Lovelace and Mendeleev found value in thinking at the level of general pattern rather than specific instance. The connection is not one of influence but of shared intellectual orientation: the conviction that patterns above the level of individual cases are real, important, and worth finding.
Anticipates
Lynn Margulis
Mendeleev and Margulis, separated by a century, are both examples of scientists who proposed a novel organising framework and waited for it to be accepted as evidence accumulated. Mendeleev left gaps predicting elements that were later found; Margulis argued for the symbiotic origin of eukaryotic cells at a time when the idea was dismissed, and lived to see it vindicated by molecular evidence. Both show that major scientific shifts often depend not only on finding the right idea but on holding it patiently until the evidence catches up. The comparison illuminates a common feature of how new scientific frameworks actually enter their fields.
Further Reading

For primary sources

Mendeleev's published papers and the translated selections from his textbook The Principles of Chemistry are available in English.

For scholarly depth

The journals Ambix and Isis have published extensive work on Mendeleev and the periodic table. The debate over priority with Lothar Meyer is traced in detail in Gordin and in several other specialist studies. Work on the Russian context of Mendeleev's science includes contributions by Nathan Brooks and Daniel Alexandrov.