This topic summary covers Knowledge Organiser: Development of the Periodic Table within Development of Periodic Table for GCSE Chemistry. Revise Development of Periodic Table in Atomic Structure for GCSE Chemistry with 20 exam-style questions and 21 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 13 of 13 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Development of the Periodic Table
Key Scientists
- Döbereiner (1817): Triads — groups of 3 by mass
- Newlands (1866): Octaves — every 8th element similar
- Mendeleev (1869): Gaps, predictions, swaps
- Moseley (1913): Ordered by atomic number
Must-Know Facts
- Early tables: ordered by atomic mass (wrong basis)
- Mendeleev left gaps for undiscovered elements
- Mendeleev predicted properties of missing elements
- Predictions confirmed by discovering gallium, germanium, scandium
- Modern table: ordered by atomic number (protons)
- Noble gases added in 1890s as Group 0
Why Mendeleev Succeeded (4-mark answer)
- Left gaps for undiscovered elements (rather than forcing elements into wrong groups)
- Made predictions about the properties of missing elements (e.g. eka-silicon)
- Swapped elements out of strict mass order when properties demanded it
- Predictions were confirmed when gallium (1875) and germanium (1886) were discovered — this provided evidence for his table
Common Mistakes
- Saying Mendeleev's table was ordered by atomic number: He used atomic mass — Moseley introduced atomic number ordering in 1913
- Forgetting Mendeleev swapped some elements: He placed tellurium before iodine despite iodine's lower mass, because properties mattered more than strict mass order
- Saying Newlands was accepted: His Law of Octaves was ridiculed by the Chemical Society — it broke down at element 21 (scandium) where the pattern of repeating properties every 8 elements failed
- Noble gases "missing" from Mendeleev's table: They hadn't been discovered yet (argon found 1894) — this was not an error, it was a gap in human knowledge
Practice questions for Development of Periodic Table
John Newlands proposed the Law of Octaves in 1866. What did he notice about the elements?
Give two reasons why Newlands' Law of Octaves was not accepted by the scientific community at the time.
Quick recall flashcards
How is the modern table arranged?
By atomic number (protons), not atomic weight
When were noble gases discovered?
1890s — added as Group 0