Mendeleev placed tellurium (relative atomic mass 127.6) before iodine (relative atomic mass 126.9). This put iodine in the same group as chlorine and bromine.
Why does the modern Periodic Table keep tellurium before iodine?
Tellurium atoms have fewer neutrons than iodine atoms.
Tellurium has a lower relative atomic mass than iodine.
Tellurium atoms have a lower atomic number than iodine.
Tellurium atoms have more electron shells than iodine.
64 exam-style questions on OCR GCSE Chemistry 2.2 Bonding, covering 2.2.1 Metals, non-metals and the Periodic Table, 2.2.2 Types of chemical bonding and dot and cross diagrams, 2.2.3 Limitations of bonding models, and 2.2.4 Reactivity, atomic number and the modern Periodic Table. Each one has a worked solution and a mark scheme showing where the marks go.