How the periodic table was built
From nine ancient metals to 118 elements: 350 years of puzzles, bold guesses and brilliant discoveries.
- Ancient times
The first nine elements
Carbon, sulfur, iron, copper, silver, tin, gold, mercury and lead were known and used long before anyone called them elements.
- 1669
The first named discoverer
Hennig Brand boils down urine looking for gold and finds glowing phosphorus instead: the first element discovered by a known person.
Find out more - 1789
Lavoisier's list
Antoine Lavoisier publishes a list of 33 “simple substances”. Most are true elements, though it also includes light and heat.
- 1808
Dalton's atoms
John Dalton argues that each element is made of its own kind of atom with its own mass, giving chemists something to measure.
- 1829
Döbereiner's triads
Johann Döbereiner notices groups of three similar elements, like calcium, strontium and barium, where the middle one's mass is about the average of the other two.
- 1860
The Karlsruhe Congress
Chemists from across Europe meet and agree on reliable atomic masses, the data needed to find patterns.
- 1865
Newlands' octaves
John Newlands spots that properties repeat every eighth element, like notes in music. Other chemists laugh at the idea.
- 1869
Mendeleev's table
Dmitri Mendeleev arranges the 63 known elements into a table, leaves gaps, and boldly predicts the properties of elements not yet found. Lothar Meyer publishes a similar table in 1870.
- 1875–1886
Predictions come true
Gallium (1875), scandium (1879) and germanium (1886) are discovered, matching Mendeleev's predictions remarkably closely.
Find out more - 1894–1898
A whole new group
William Ramsay and colleagues discover argon, helium, neon, krypton and xenon. The table gains a new column: the noble gases.
Find out more - 1913
Moseley's X-rays
Henry Moseley shows that each element's true place is set by its atomic number, the number of protons. He was killed in the First World War two years later, aged 27.
- 1937
The first man-made element
Technetium is created in a laboratory, filling a gap that nature had left almost empty.
Find out more - 1944–1945
Seaborg's new row
Glenn Seaborg proposes moving the actinides into their own row below the lanthanides, giving the table the shape we use today.
Find out more - 2016
Row seven complete
Nihonium, moscovium, tennessine and oganesson are officially named, completing the seventh row with 118 elements.
Find out more - 2019
Happy 150th birthday
The United Nations celebrates the International Year of the Periodic Table, 150 years after Mendeleev's first version.
Mendeleev's predictions vs reality
Eka-aluminium → Gallium (1875)
| Property | Predicted | Found |
|---|---|---|
| Atomic mass | about 68 | 69.7 |
| Density | 5.9 g/cm³ | 5.9 g/cm³ |
| Melting point | low | 29.8 °C |
Eka-silicon → Germanium (1886)
| Property | Predicted | Found |
|---|---|---|
| Atomic mass | about 72 | 72.6 |
| Density | 5.5 g/cm³ | 5.3 g/cm³ |
| Oxide formula | EsO₂ | GeO₂ |