# The order of the elements

- kind: problem
- status: solved (evidence tier V3)
- year: 1817

**Statement.** Is there an organizing principle behind the chemical elements?

Mendeleev left gaps for elements not yet found and predicted their properties; gallium, scandium and germanium filled them within 17 years. Moseley's X-ray measurements showed the order was nuclear charge, not weight. Quantum mechanics later explained why the pattern exists.

*Evidence tier V3 is the import default for a result the curation records as settled in the published record. No formal proof or certificate is attached to this page yet.*

Closed 1869, Dmitri Mendeleev; 1913, Henry Moseley ties order to atomic number.

## Sources

- [Wikipedia: Periodic table](https://en.wikipedia.org/wiki/Periodic_table)

[Materials](/wiki/Space:materials.md) · [Chemistry and matter](/wiki/Continent:chemistry.md)

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