# Mendeleev arranged elements into a periodic table in 1869. His table was different from the modern periodic table. Explain how Mendeleev arranged elements in his table and describe two ways in which the modern periodic table differs from Mendeleev's original table.

> Edexcel A-Level Chemistry (9CH0) — 1.2 Periodic table and trends · Explain · 5 marks

> When Mendeleev published his periodic table in 1869, not all elements had been discovered. He made predictions about undiscovered elements such as eka-silicon, which was later found to be the element germanium.

## Mark scheme (5 marks)

1. Mendeleev arranged elements in order of relative atomic mass (atomic weight)
2. Mendeleev left gaps in his table for undiscovered elements / predicted the existence and properties of undiscovered elements
3. The modern periodic table is arranged in order of atomic number (proton number) rather than relative atomic mass
4. The modern periodic table includes more elements / all currently known elements have been discovered and placed
5. The noble gases (Group 0) are included in the modern periodic table but were not in Mendeleev's table / a new group was added

## Key terms

- [periodic table](https://www.gradenine.co.uk/glossary/periodic-table)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/mendeleev-arranged-elements-into-a-periodic-9980a983) · Published by Druglandscape Ltd.