Six tips for teaching chemical formulas

Some formulas are well known. If ‘CO₂’ and ‘H₂O’ are read aloud even some young secondary school pupils will be able to give their names, although fewer will be able to accurately write the formulas. The rules, which are automatic to teachers, may seem unduly complicated and petty to students.

Some elements have just one capital letter as their symbol, others have a capital and a lower case letter. Subscript numbers multiply the element symbol to their left only, unless there are brackets. This contrasts with numbers in algebraic equations in maths, which appear as ordinary characters and multiply the letter to their right. An added complication for more advanced students, who are learning functional groups, is that some formulas are empirical, whereas others are expanded into structural or semi-structural forms. For example, ethanol can be written as CH₃CH₂OH or C₂H₅OH but seldom as C₂H₆O. As students progress they may also see state symbols to the right of the formula.

Chemical formulas are part of our language, so it makes sense to explore teaching techniques for modern foreign languages.

1. Share reasons

It is important that students know why they need to learn formulas. A good reason is that word equations have limitations; the same substances have different names in different languages.

• English: Copper sulfate
• French: Sulfate de cuivre
• German: Kupfersulfat
• Spanish: Sulfato de cobre

To avoid confusion, chemists use symbol equations to show what is happening in chemical reactions because chemical formulas describe substances in terms of the elements they contain.

2. Learn and assess formulas in isolation and in context

Learning and testing lists of formulas is a legitimate exercise but it can be tiresome and demotivating for students. Design vocabulary lists of formulas carefully with a medium-term plan and your class’s needs in mind. Pupils aged 11–14 might learn the formulas of hydrochloric, sulfuric and nitric acids, sodium hydroxide and ammonia as their vocabulary in a topic on acids and alkalis. It is important to quickly move this isolated vocabulary into context by combining it with other skills and knowledge so that students see its utility.

For example, show students an image of a flask labelled ‘NaOH’. Ask students:

• How many different elements are present in the formula for the substance in the flask?
• Suggest a pH for the substance in the flask.
• What state symbol would be appropriate for the substance?

3. Emphasise patterns

There are rules within formulas – just like there are grammatical rules within languages. For example, emphasise that the suffix ‘-ate’ means there is oxygen in the formulas, and ‘carbonate’ means there is a ‘CO₃’ group of atoms.

4. Little, often and early

Although the ability to acquire new vocabulary does not decline as students get older, there are benefits to introducing scientific language early on. Early learning maximises opportunities to practise manipulating formulas and apply understanding, and firmly weaves the language of chemistry into its theory and practice. Activities to practice formulas make handy quick-start activities to settle students into a lesson. It is also worth having a few such tasks ready as an emergency filler or to help keep students on task when practical work requires waiting around.

5. Add variety

Language lessons tend to be multimodal. Students experience vocabulary in reading, writing, listening and speaking work. There are lots of opportunities to work with formulas in routine teaching, especially in practical work. Activities don’t have to be restricted to written exercises: card sorts, games and interactive quizzes can all add variety.

Go fish!

Try a version of the card game Go fish!, using cards showing chemical formulas instead of regular cards to help pupils become fluent in associating formulae with the names of substances. Download teacher notes with printable cards (MS Word or pdf) and a set of instruction slides for students (ppt or pdf).

6. Engage parents

Many parents test their children on their modern language vocabulary and parental input can be a key factor in student success. Many parents will lack fluency with formulas themselves so provide suitable materials for them to use at home. Flashcards, formula vocabulary lists, example questions and answers, as well as Google quizzes are all useful resources for this.