Structure and formulae of alkanes (AQA GCSE Chemistry & Combined Science)

This lesson introduces the alkanes as a group of hydrocarbons and explains how to draw their displayed formula and work out the general formula. The PowerPoint is part of the second lesson in a series of 2 which have been designed to cover point 7.1.1 of the AQA GCSE Chemistry & Combined Science specifications.

The students were introduced to crude oil and hydrocarbons in the previous lesson so this one begins by introducing the fact that most of the hydrocarbons in crude oil are alkanes. The students are challenged to recall that covalent bonds will hold hydrogen and carbon together and they will learn that every carbon atom has four covalent bonds. This fact is used in the step by step guide as they are shown how to draw the displayed formula for methane. Moving forwards, a quick competition is used to introduce the next three members of the group in ethane, propane and butane, and the students have to apply their understanding by drawing the formula to find the molecular formula. The general formula for the alkanes is determined and then a series of exam questions will challenge them to apply this to work out numbers of carbon or hydrogen atoms or to write a formula.