Edexcel GCSE Chemistry Topic 1: Key Concepts in Chemistry Exam Questions

About Edexcel GCSE Chemistry Topic 1: Key Concepts in Chemistry

Topic 1 of Edexcel GCSE Chemistry contains the foundation ideas used across the whole course: atomic structure, the periodic table, ionic and covalent bonding, the properties of different types of substance and calculations involving masses. Because these ideas are needed everywhere, Topic 1 is assessed on both Paper 1 and Paper 2. You learn the development of the atomic model, isotopes and relative atomic mass, dot and cross diagrams, giant and simple structures, the forms of carbon, and quantitative work including empirical formulae, conservation of mass, concentration and, at Higher tier, moles and limiting reactants. Calculations and explanations of properties in terms of structure are tested heavily.

What you need to know

• Atomic structure Atoms contain protons (relative mass 1, charge +1), neutrons (relative mass 1, charge 0) and electrons (relative mass 1/1836, charge -1). Dalton, Thomson, Rutherford and Bohr developed the model; the nucleus is tiny compared with the atom. Isotopes have the same number of protons but different numbers of neutrons; relative atomic mass is calculated from isotope abundances.
• The periodic table Mendeleev arranged elements by atomic mass, left gaps and predicted properties of undiscovered elements. Today elements are arranged by atomic number; the group number gives the outer electrons and the period gives the number of shells.
• Ionic bonding Electrons are transferred from metal to non-metal atoms, forming ions with stable electronic configurations. Ionic compounds form lattices held by strong electrostatic forces; know ions ending in -ide and -ate.
• Covalent bonding and types of substance A covalent bond is a shared pair of electrons. Simple molecular substances have low melting points due to weak intermolecular forces; giant covalent substances (diamond, graphite) have high melting points. Graphene and fullerenes, polymers and metals with delocalised electrons are also covered.
• Calculations involving masses Calculate relative formula mass, empirical formulae from masses, and concentration in g dm-3. Explain mass changes in open and closed systems using conservation of mass.
• Moles (Higher tier only) One mole contains 6.02 x 10^23 particles (the Avogadro constant). Use moles = mass / Mr to calculate reacting masses, deduce balanced equations from masses and identify limiting reactants.

Common mistakes in Topic 1: Key Concepts in Chemistry

• Confusing the mass number with the relative atomic mass. Relative atomic mass is a weighted mean, so it is often not a whole number.
• Saying simple molecular substances have low boiling points because covalent bonds are weak. The covalent bonds are strong; the intermolecular forces are weak.
• In empirical formula calculations, dividing by atomic number instead of relative atomic mass.
• Saying graphite conducts because of ions. It has delocalised electrons between layers.
• Forgetting to convert cm3 to dm3 when calculating concentration in g dm-3.

Try three Topic 1: Key Concepts in Chemistry exam-style questions