Dmitri Mendeleev

Author of the Periodic Table · Chemist · 1834–1907

The Russian chemist who arranged the elements into the periodic table — trusting the pattern so far that he left gaps and correctly predicted elements not yet discovered.

Who was Mendeleev?

Dmitri Mendeleev, born in Tobolsk in Siberia as the youngest of many children, was carried across Russia by a determined mother to be educated. A chemist of restless breadth, he sought the order behind the sixty-odd elements then known. Arranging them by atomic weight, he saw their properties recur in periods — and trusted that pattern so far that he left empty spaces for elements not yet found, and predicted the properties of 'eka-aluminium' and 'eka-silicon'. When gallium and germanium were discovered and matched his forecasts, the periodic law was vindicated. He also worked on petroleum, agriculture and Russian industrial standards. Famously, he was never awarded the Nobel Prize, missing it by a single vote.

Major achievements

• Formulated the periodic table of the elements (1869)
• Predicted the existence and properties of undiscovered elements, later confirmed (gallium, germanium, scandium)
• Trusted the periodic law enough to correct some accepted atomic weights
• Advanced Russian petroleum chemistry, agriculture and metrology
• Wrote an influential textbook, 'The Principles of Chemistry'

Life in brief

• 1834 — Born in Tobolsk: The youngest of many children, in Siberia.
• 1855 — Graduates in St Petersburg: Trains as a chemist and teacher.
• 1869 — The periodic table: Arranges the elements and leaves gaps for the undiscovered.
• 1875 — Gallium found: Matches his 'eka-aluminium' prediction.
• 1886 — Germanium found: Matches his 'eka-silicon' prediction.
• 1906 — Misses the Nobel: Reportedly by a single vote.
• 1907 — Dies: In St Petersburg.

Explore the life of Mendeleev — five chapters

1. A Journey Across a Continent — Siberia, a burned glassworks, and a mother's determination
2. 17 February 1869 — A textbook problem, and a table drawn in a day
3. The Gaps — Describing three elements before anyone found them
4. Balloons, Oil and Standards — A chemist who would not stay in the laboratory
5. The Table Since — Noble gases, atomic number, and an element with his name

Read the five-chapter life of Dmitri Mendeleev →

Where Mendeleev appears in your course

Dmitri Mendeleev has a genuine claim on 13 lessons of the Pearson Edexcel International GCSE science course built into Incandio. Six of them:

• The Three States of Matter — Chemistry: Mendeleev built the Periodic Table on the conviction that matter is made of discrete atoms with fixed, comparable masses — an idea still openly disputed when he began. Without that commitment there is no way to say what a solid, a liquid or a gas actually IS.
• Electronic Configurations and the Periodic Table — Chemistry: Mendeleev arranged the known elements by their properties, then left empty spaces where he believed undiscovered elements must sit — and predicted their densities and melting points in detail. He was right, and that is why the table is a scientific theory rather than a filing system.
• Solubility and Solubility Curves — Chemistry: Long before the periodic table, Mendeleev's doctoral research was on solutions, and he argued that dissolving is not simple mixing but involves real interaction between solvent and solute. That is the argument underneath this lesson's particle explanation of saturation, and he pursued it for years against people who thought solutions were merely stirred-together substances.
• Formulae and Balanced Equations — Chemistry: Mendeleev arranged the elements by relative atomic mass and found that their properties repeated — and where a mass did not fit the pattern he was prepared to say the measured mass was WRONG rather than the pattern. Several times he turned out to be right. The Ar values you add up in this lesson are the numbers he staked his reputation on.
• Ionic Bonding — Chemistry: The most useful idea on this page is that the charge of an ion can be read off the group number, and that only works because the periodic table is arranged the way it is. Mendeleev built it by ordering the elements and noticing that properties repeat — and he trusted the pattern enough to leave GAPS for elements nobody had found, predicting their properties in detail. When gallium and germanium turned up and matched, the table stopped being a filing system and became a prediction. He is the right person to ask why elements in the same column behave alike, and how much you can safely infer from a pattern.
• Giant Covalent Structures — Chemistry: Diamond and graphite are the sharpest challenge to the idea that an element has fixed properties — same atoms, same bonds, utterly different substances. Mendeleev built the periodic table on the principle that properties are systematic rather than arbitrary, and he trusted that principle so far that he left gaps for undiscovered elements and predicted their densities and melting points in advance. He is the right person to ask what an element's properties actually belong to, and how far you can predict a substance you have never seen from the way its atoms are arranged.

Debate Mendeleev in the Agora

Reading is the start. On Incandio an idea counts as mastered only once you have argued it against the person with the strongest claim on it, in structured rounds marked against published descriptors.

• The Gaps He Left — “The periodic table is a way of organising the elements we know, not a source of new knowledge.”

Teach what Mendeleev discovered

The Order Beneath the Elements — ideas Mendeleev is tied to on the Living Knowledge Map. On Incandio you prove you understand one by teaching it to Ember, the AI pupil, in Teach the Room.

Begin

• Start a conversation with Mendeleev — a dramatised, historically grounded AI portrayal
• Read the Historical Brief
• Explore the life of Mendeleev — five chapters
• Find your exam topics · Meet all 208 figures