Errors Students Make When Writing Chemical Formulas

5/25/2018

The Problem: Students have trouble balancing charges in chemical compounds

The first MAJOR hurdle students come to in chemistry is when they have to start writing chemical formulas when given a chemical name. They seem to do better if you give them a chemical formula and have them write a name, but give them a name and they seem to have a harder time.

#1 Solution: Dive deep into subscripts and charges

I think it is because students are just really uncomfortable with subscripts at this point in their chemistry knowledge.

Draw it out for them using circles for the cations and anions. Explain that if you have to draw more than one circle for each cation or anion then you would use a subscript. Two cations would equal a 2 subscript, 3 cations would equal a 3 subscript etc.

When you start out explaining how to name compounds you probably use HCl or NaCl or something like that because they each have opposing charges of one and (1+) and (1-) equals zero, right?

Solution #2 Don't let them mess with polyatomic ions

Your students need to really understand that polyatomic ions are like conjoined twins. The atoms move together and can't be separated! It seems that my students want to add in or take away from the polyatomic ions and they just can't.

When you draw out the cations and anions to show how balancing charges work, make sure to draw the anions out as a single circle-even if they are polyatomic ions.

Solution #3:Have students actually memorize their polyatomic ion list

Some students at this point just haven't learned their polyatomic ions. Have them make a Quizlet or Kahoot on that topic. Or, have them work a large packet that forces them to practice using the polyatomic ions.

Solution #4: Polyatomic ions always have the same charge and that charge is not on the periodic table

Other students are having trouble with the idea that polyatomic ions function as a unit, since they look just like the other elements. I really like this worksheet for that.

I have a another worksheet that goes along with this here. It's organized very visually.

I really like these two images for students and will probably make a worksheet based on them in the future.