Which discovery provided the modern basis for ordering the periodic table and resolved mass-order anomalies?
electrons have negligible mass
compounds contain fixed mass ratios
neutrons are uncharged
proton number is unique to each element
80 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.