Edexcel GCSE Combined Science CC1 Key concepts in chemistry: a complete overview of atomic structure, the periodic table and bonding

What CC1 actually demands

Key concepts in chemistry is the foundation of Edexcel Combined Science chemistry, examined on both chemistry papers. The examiners reward accurate atomic-structure calculations, a clear understanding of isotopes, and confident links between bonding, structure and properties, which is the single most important idea in GCSE chemistry.

This guide walks through the two halves of the topic and ties together the matching dot-point pages, each with its own practice questions.

Atomic structure and the periodic table

An atom has a nucleus of protons and neutrons, surrounded by electrons in shells. The atomic number is the number of protons; the mass number is protons plus neutrons; neutrons = mass number minus atomic number. Isotopes have the same protons but different neutrons.

Electrons fill shells (2, 8, 8). The periodic table is ordered by atomic number: groups (columns) share outer electrons and properties; periods (rows) share the number of shells.

Bonding, structure and properties

The three bond types and the structures they form explain everything about a substance's properties:

• Ionic (metal + non-metal): electrons transferred, giant lattice of ions. High melting points; conducts when molten or dissolved.
• Covalent (non-metal + non-metal): electrons shared. Simple molecules have low melting points and do not conduct; giant covalent structures (diamond, graphite) are very strong.
• Metallic: positive ions in a sea of delocalised electrons. Conducts electricity and heat; malleable.

How CC1 is examined

• Calculations. Working out protons, neutrons and electrons from atomic and mass numbers.
• Isotopes. Defining them and explaining their identical chemistry.
• Configurations. Writing electronic configurations and reading off the group.
• Structure and properties. Explaining melting points and conductivity from the bonding.

Check your knowledge

A mix of recall and explanation questions covering CC1. Attempt them under timed conditions, then check against the solutions.

1. What does the atomic number of an element tell you? (1 mark)
2. How do you calculate the number of neutrons in an atom? (1 mark)
3. Define isotopes. (2 marks)
4. Write the electronic configuration of sodium (11 electrons). (1 mark)
5. State the type of bonding between a metal and a non-metal. (1 mark)
6. Explain why simple molecular substances have low melting points. (2 marks)
7. Explain why metals conduct electricity. (2 marks)
8. Why does an ionic compound conduct only when molten or dissolved? (2 marks)