Formal Charge Practice Problems with Explanations

A video of formal charge practice problems (from easy to difficult) with clear, concise answers and explanations.

Calculating the formal charges for a molecule is a reasonably reliable way to tell what the most favorable LS is in the real world.

We start with a Lewis Structure and then calculate the charges for each atom. The most favorable or “best” Lewis Structure for a molecule is the one with formal charges closest to zero. Zero is even better.

We’ll use the equation:

Formal charge = [# of valence electrons] - [nonbonding val electrons] - [bonding electrons / 2]

The number of valence electrons for the atom of interest is found on the Periodic Table.

Nonbonding valence electrons are those around the atom of interest that are not involved in chemical bonds (they aren't being shared with another atom).

Bonding valence electrons are the ones shared between atoms. We'll divide this number by two.

Some things to note about Formal Charges:

- Formal charge is different from the oxidation number!
- If you can exceed the octet rule for the central atom it's a good idea to check the formal charges.
- If we have isomers or resonance -- formal charges will help us determine most stable structure.
- The closer the formal charges are to zero the more likely we have the most favorable Lewis structure for the molecule.
- We write the formal charges in (). E.g. (-1)

Helpful Videos:

Drawing/writing done in InkScape. Screen capture done with Camtasia Studio 4.0. Done on a Dell Dimension laptop computer with a Wacom digital tablet (Bamboo).

[tomeee]

You're a teaching god. I went from not knowing any of my class's materials for the past week to knowing all of it in under 20 minutes. Well done

[comradeuu]

Your videos really helped me in my first year of college and my first chemistry exam. Now, after my last biochemistry exam a few weeks ago I rewached your videos and realized how easy and basic the former hard suff suddenly became. Thanks for your teaching, keep up the good work and greetings from Germany!

[ThaoTrangPhotography]

THANK YOU SO MUCH! After watching 10 minutes of your video, I understand it so much better than reading my college textbook! You are amazing! This was by far the most simple and straightforward video ever. Nice and clean example.

[ravinduwijayarathna]

Awesome video, most of the videos on internet explains formal charge based on its equation.. none of them ever explained why formal charge is important..

[raje]

Thankyou sir this helped me for my JEE exam

[KushagraVyas-jb]

Thanks sir for this video because in my school exams these type of questions are mostly asked. I never know what is formal charge and how it should be calculated, I always make mistakes in between calculating FC. But after watching this I am glad that I can do any problems based on this topic.

[kevinhevans]

Thank you! That was a very helpful video. I'm preparing for the ACS exam and I feel like this was something I never truly learned until now!

[fransseakamela]

thank you for the clear explanation and workout my lecturer was doing senseless things..thank and God bless you

[sarthpetkar]

Because of you it is easy to understand the concept in limited time

[sumrikdewanji]

Thank you Sir . Scientific Reasons for the importance of formal charge .

[thekambIer]

Is there any order to writing the calculations? Example: do you do least valence electron atoms to most valence electron atoms when writing them down on paper?

[seemabajpai]

Awesomely explained sir,
I was here for just to try these questions...

[sharvani]

You are a fabulous teacher Dr.B love from India!

[maximchowdhury]

I think that instead of "1/2 bodned electrons", we can use "the number of lines attached to it"

[kgosigadimokgethi]

So whatever atom that is below period 3 can form expanded octets?

[brothersofosman]

Hey can you please help we workout of the molecule N=N=N
in which the 1st and last nitrogen atoms have 2 lone pairs each.
Please let me know.
Thanks

[SomeRndomGuyzz]

I took chemistry last year and your channel was super useful. Thanks. I'm unsubscribing now because my academic interests are more language-related, but I hope you continue making these.

[strangergranger]

I want to learn this and I don't if I am going to take this subject in college. I just want to have a self study. How can I start? I mean I want to know it chronological order can you help me? By the way this video is awesome!

[prachichanda]

Sir are 2 oxygen atoms bonded to nitrogen by dative bond in NO3-?is that why all 5 electrons of nitrogen are used up?
Also thank you for Making chemical bonding so much easier for me 😄

[yajatyadav]

for the last problem, why can't you have ONE double bond and 2 single bonds with the oxygen? That way, all atoms have eight electrons in their valence shells. Xenon will just have a lone pair on it.