Three elements, Q, R and T, are among the first 20 elements. The letters are not the chemical symbols of the elements.
An atom of Q has three occupied shells and three electrons in its outer shell.
R forms an ion, R2+\mathrm{R^{2+}}R2+, which has the electronic configuration 2.8.8.
T forms an ion, T−\mathrm{T^{-}}T−, which has the same electronic configuration as a neon atom.
Deduce the atomic number of Q.
Deduce the group and period of R and identify the element.
Deduce the electronic configuration of an atom of T and identify the element.
Explain how the electronic configurations of the first 20 elements account for the way these elements are arranged in periods and groups in the modern periodic table.
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.