The atomic & mass numbers (Edexcel GCSE Chemistry & Combined Science)

This lesson describes the meaning of the atomic and mass number and explains how to calculate the number of protons, neutrons and electrons. The PowerPoint has been designed to cover the detail of points 1.4, 1.7, 1.8 and 1.10 of the Edexcel GCSE Chemistry and Combined Science specifications.

The lesson begins by challenging the students to put the chemical symbols for astatine, oxygen, iodine and carbon together to form the word atomic. Time is taken to explain the meaning of the atomic number and to emphasise how the number of protons in the nucleus is unique to atoms of that element. The students will learn that as the number of electrons is always the same as the number of protons in an atom, the atomic number can be used to calculate the numbers of both of these particles. Moving forwards, the mass number is considered and having been given the number of neutrons in a lithium atom, the students are challenged to articulate how the mass number and atomic number were used in this calculation. A series of worked examples are done as a class before the students are given the opportunity to challenge their understanding.