Writing+formula

=Writing formula=

This seems to be a big headache for some students.

You need to work to get it right. Once you have mastered this it will enable you to tackle so many more questions.

There are some basic formula you need to learn - you will be given a list of these. But once you have learnt them, the basic rules for writing formula are the same:


 * Identify the symbols of the cation and anion e.g. sodium is Na and Oxide is O


 * Identify the charge for each and place above the symbol


 * For sodium that would be +1 and for Oxide that would be -2


 * Balance the positive and negative charges


 * Since each sodium is +1 and each Oxide is -2 then it will take two Na+ to balance one oxide with a -2 so that 2(+1) + 1(-2) = 0.


 * Write the formula placing the subscripts right after the symbol they go with.

You can use these links to practise writing formula.

Basic formula practise.

Multiple choice format - with tutorial to help you check your answers

Multiple choice format - select the correct formula

More advanced formula - you may need to use your learning list initially for these, but you should be able to do these unaided by half-term.