When you start Chemistry GCSE, it’s easy to get confused about when and how to use brackets in chemical formulae. If you sometimes find yourself scratching your head on the topic of brackets, this short blog will help you out…
First off, elements and simple compounds never need brackets.
C is carbon. O2 is oxygen. NO2 is nitrogen dioxide. CH4 is methane. Al2O3 is aluminium oxide.
No brackets. That’s it. Simple!
Brackets are only needed for compounds formed from complex ions. But what is a complex ion? Well, it’s an ion that is made up of more than one element.
The most common examples of complex ions are:
You’re expected to know the formulae of these complex ions (and their charges) for the exam.
Examples: NaOH MgSO4 NH4 NO3 CaCO3
The reason is that you need to put a bracket around the complex ion to show how many of those whole complex ions there are in the compound.
Examples: Mg(OH)2 Al2(SO4)3 (NH4)2SO4
That’s it for brackets! Except that if you’re not sure how to decide whether there’s only one ion in a compound, or two or three, then have a look here: Top tips for writing chemical formulae where you’ll learn about balancing the charges of positive and negative ions.
Best of luck!