Edexcel IGCSE Chemistry

Revision Notes

1.3.1 Atoms: Definitions & Structure

Atoms & Molecules

  • It is important to understand the terms atom and molecule when referring to atomic structure, elements and compounds

Atoms & Molecules Definitions Table

Atoms & Molecules Definitions Table, downloadable IGCSE & GCSE Chemistry revision notes

The Structure of the Atom

  • Elements are made of tiny particles of matter called atoms
  • Each atom is made of subatomic particles called protons, neutrons and electrons
  • Their size is so tiny that we can’t really compare their masses in conventional units such as kilograms or grams, so a unit called the relative atomic mass is used
  • One relative atomic mass unit is equal to the mass of a carbon-12 atom.
  • All other elements are measured relative to the mass of a carbon-12 atom and since these are ratios, the relative atomic mass has no units
  • Hydrogen for example has a relative atomic mass of 1, meaning that 12 atoms of hydrogen would have exactly the same mass as 1 atom of carbon
  • The relative mass and charge of the subatomic particles are shown below:

The Mass & Charge of Subatomic Particles Table

Atomic Structure & the Periodic Table table, IGCSE & GCSE Chemistry revision notes

Exam Tip

The mass of an electron can just be stated as ‘negligible’ or ‘very small’ in an exam. You do not need to learn the value.

Key Terms

  • You need to know the following terms to describe the properties and characteristics of atoms

Atomic Structure Key Terms Table

Atomic Structure Key Terms, downloadable IGCSE & GCSE Chemistry revision notes

Exam Tip

The term nucleon number is an alternative to mass number and means the same thing. A nucleon is a collective name for protons and neutrons.

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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