Mendeleev placed tellurium (relative atomic mass 127.6) before iodine (relative atomic mass 126.9), so that iodine was in the same group as chlorine and bromine.
Which statement explains, in modern terms, why this order is correct even though it breaks the order of relative atomic mass?
Te has more protons than I, and its atoms have fewer neutrons on average
Te has fewer protons than I, and its atoms have more electrons on average
Te has the same number of protons as I, but more neutrons on average
Te has fewer protons than I, and its atoms have more neutrons on average
50 exam-style questions on Edexcel GCSE Chemistry 2.2 The periodic table, covering 2.2.1 Mendeleev's periodic table, 2.2.2 Periods, groups, metals and non-metals, and 2.2.3 Electronic configuration and position in the periodic table. Each one has a worked solution and a mark scheme showing where the marks go.