Edexcel International GCSE Chemistry Section 1: Principles of Chemistry Exam Questions

About Edexcel International GCSE Chemistry Section 1: Principles of Chemistry

Section 1 of Edexcel International GCSE Chemistry (4CH1) is the largest section of the course and underpins everything else. It covers states of matter and diffusion, separating mixtures, atomic structure and isotopes, the periodic table, chemical formulae, equations and calculations, ionic, covalent and metallic bonding, and electrolysis. Content is assessed on both papers, with content shown in bold in the specification assessed on Paper 2 only. Examiners use this section for a large share of calculation marks: relative atomic mass from isotopes, moles, reacting masses, empirical formulae, percentage yield, concentration and gas volumes, so careful, well-set-out working is essential.

What you need to know

• States of matter and mixtures Describe the arrangement, movement and energy of particles in solids, liquids and gases, and explain diffusion and dilution experiments. Separate mixtures by simple distillation, fractional distillation, filtration, crystallisation and paper chromatography, calculating Rf values.
• Atomic structure Protons, neutrons and electrons with their relative masses and charges; atomic number and mass number; isotopes; calculating relative atomic mass from isotopic abundances. Electronic configurations for the first 20 elements, for example 2,8,8,2 for calcium.
• The periodic table Elements are arranged in order of atomic number. Group number gives the number of outer electrons and period number gives the number of shells. Metals form basic oxides and non-metals form acidic oxides; noble gases are unreactive because of full outer shells.
• Formulae, equations and calculations Write balanced equations with state symbols. Use moles = mass / Mr, reacting masses, empirical and molecular formulae, percentage yield, concentration in mol dm-3 and g dm-3, and molar volume of a gas (24 dm3 at room temperature and pressure).
• Ionic bonding Ions form by electron transfer; ionic compounds are lattices held by strong electrostatic attractions between oppositely charged ions, giving high melting points and conductivity when molten or in solution.
• Covalent and metallic bonding Covalent bonds are shared pairs of electrons. Simple molecular substances have low melting points because of weak intermolecular forces; giant covalent substances such as diamond, graphite and C60 fullerene must be explained from their structures. Metals have positive ions in a sea of delocalised electrons, so they are malleable and conduct electricity.
• Electrolysis Ionic compounds conduct when molten or in aqueous solution because the ions are free to move. Predict products at the cathode and anode for molten compounds and aqueous solutions, and write half equations such as 2Cl- → Cl2 + 2e-.

Common mistakes in Section 1: Principles of Chemistry

• Using the mass number rather than the weighted mean when asked for relative atomic mass from isotope data.
• Saying simple molecular substances have low melting points because covalent bonds are weak. The intermolecular forces are weak; the covalent bonds are strong.
• Rounding the mole ratio too early in empirical formula questions, for example treating 1 : 1.5 as 1 : 2 instead of 2 : 3.
• Saying ionic solids conduct electricity. Ions are fixed in the lattice; they only conduct when molten or dissolved.
• Writing half equations with electrons on the wrong side, or unbalanced charges.

Try three Section 1: Principles of Chemistry exam-style questions