Isotopes (Edexcel GCSE Chemistry & Combined Science)

This lesson describes the meaning of an isotope and explains how to calculate the relative atomic mass using the relative masses and abundance of its isotopes. The PowerPoint and accompanying resources have been designed to cover the detail of points 1.9, 1.11 & 1.12 of the Edexcel GCSE Chemistry & Combined Science specifications.

The early topic 1 lessons covered the meaning of the atomic and mass number and the calculation of the number of subatomic particles, and this lesson begins by challenging the recall of this key information. Moving forwards, a quick quiz competition is used to introduce the term “isotope” and then the students have to calculate the number of subatomic particles in K-39, K-40 and K-41 before using their answers to complete a definition about these types of substances. Time is taken to explain how isotopes are represented in standard annotation and the importance of the mass number is emphasised. A series of application questions are used to challenge them to apply their understanding and knowledge and mark schemes are embedded into the PowerPoint to allow the students to self-mark.
The remainder of the lesson explains how the existence of isotopes results in some elements having relative atomic masses that are not whole numbers and then explains how these masses can be calculated. Once an example is demonstrated, the students are again given the chance to apply their understanding to a series of questions, and this exam question worksheet has been differentiated two ways