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Topic 1: Key concepts in chemistry

6 dot points across 6 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

What is an atom made of, and how do we describe and count its particles?

Atomic structure: protons, neutrons and electrons, atomic number and mass number, isotopes and relative atomic mass, and the development of the model of the atom.
A focused answer to Edexcel GCSE Chemistry topic 1, covering the subatomic particles and their relative masses and charges, atomic number and mass number, isotopes and how to calculate relative atomic mass, and how the model of the atom developed from Dalton to the nuclear model.
9 min answer →

How do we calculate formula masses, empirical formulae, reacting masses and concentrations?

Calculations in chemistry: relative formula mass, percentage by mass, empirical formulae from masses, reacting masses from balanced equations, concentration in grams per cubic decimetre, and the mole.
A focused answer to Edexcel GCSE Chemistry topic 1, covering relative formula mass, percentage by mass of an element, finding empirical formulae from masses or percentages, the empirical-formula core practical, reacting-mass calculations, concentration in g/dm3, and the definition of the mole.
10 min answer →

How do we write and balance the formulae and equations that describe a reaction?

Chemical formulae and equations: writing formulae from ions, balancing symbol equations, state symbols, ionic equations and half-equations, and the law of conservation of mass.
A focused answer to Edexcel GCSE Chemistry topic 1, covering how to write formulae from ion charges, balance symbol equations, add state symbols, write ionic and half-equations, and apply the law of conservation of mass including why mass appears to change in open systems.
9 min answer →

How do shared electrons and a sea of delocalised electrons explain covalent and metallic substances?

Covalent and metallic bonding: shared electron pairs, simple molecular and giant covalent structures (diamond, graphite, fullerenes, graphene), polymers, metallic bonding, and how each structure explains properties.
A focused answer to Edexcel GCSE Chemistry topic 1, covering covalent bonding and dot-and-cross diagrams, simple molecular substances, the giant covalent structures of diamond, graphite, fullerenes and graphene, simple polymers, metallic bonding with delocalised electrons, and how each structure explains melting point and conductivity.
10 min answer →

How do metals and non-metals transfer electrons to form ionic compounds?

Ionic bonding: the formation of ions by electron transfer, dot-and-cross diagrams, the giant ionic lattice, and how the structure explains the properties of ionic compounds.
A focused answer to Edexcel GCSE Chemistry topic 1, covering how ions form by electron transfer between metals and non-metals, writing the formulae and charges of common ions, drawing dot-and-cross diagrams, the giant ionic lattice structure, and explaining melting points, brittleness and conductivity.
9 min answer →

How is the periodic table arranged, and how does electronic configuration explain it?

The periodic table: how the elements are arranged by atomic number into groups and periods, the development of the table by Mendeleev, metals and non-metals, and electronic configurations of the first 20 elements.
A focused answer to Edexcel GCSE Chemistry topic 1, covering how the modern periodic table is arranged by atomic number, the work of Mendeleev, the meaning of groups and periods, the metal and non-metal divide, and how to write the electronic configurations of the first 20 elements and link them to group number.
9 min answer →