Question

What are some common mistakes students make when determining formulas?

Answer 1

I would say a very common error students make is forgetting to balance the charges of the ions (positive and negative) in ionic compounds.

Explanation:

For example, when aluminum and oxygen react they form the compound aluminum oxide.

This is considered an ionic compound because it contains a metallic ion (`Al^(+3)`) and a nonmetallic ion (`O^(-2)`)

So the formula of aluminum oxide needs to be `Al_2O_3` which means there are 2 Al ions paired with 3 O ions.

2 x (`Al^(+3)`) = +6
3 x (`O^(-2)`) = -6
net charge = 0

For other formula/nomenclature tips, hints and reminders check out the video below.

Video from: Noel Pauller