Quick Determination of FC [ENDORSED]

[Mia Navarro 1D]

When you have the Lewis structure of the molecule drawn out, this is one of the ways I learned to quickly find formal charge:
1. Find the number of valence electrons of the given atom based on the periodic table. (n)
2. Draw a circle around the atom in the Lewis structure; find the number of total atoms surrounding the atom. (a)
3. Subtract (n) - (a) to find the formal charge.

This understanding of the formal charge allows me to more easily understand the equation for formal charge.
Hope this helps someone out there!

[RaviAmin1H]

I think to really understand formal charge people need to know that it assumes covalent bonds are shared equally when in that's not true when atoms are electronegative. This means that at time even though due to formal charge the atom may have a full shell, but in actuality the other bonded atom pulls the electron.

[Peter Dis1G]

Thanks for both wonderful explanations!

[Mia Navarro 1D]

I think to really understand formal charge people need to know that it assumes covalent bonds are shared equally when in that's not true when atoms are electronegative. This means that at time even though due to formal charge the atom may have a full shell, but in actuality the other bonded atom pulls the electron.

This is why we split the covalent bonds when drawing the circle around the atom. Thank you for the clarification!

[AlyssaPeckham1A]

Another quick way that I determine formal charge is:
1- counting the lone pairs around the atom (each equals 2 electrons)
2- counting the bonds around the atom (each counts as 1 electron)

[Kyle Reidy 3H]

I personally found it very helpful to think about how many protons were in the nucleus of the atom. We compare this with the number of electrons surrounding the nucleus, halving any "shared" electrons. If the atom has more electrons than protons, we know the formal charge to be negative. If the numbers are the same, the charge is neutral, and if it has more protons, it's positive.

[Kyle Reidy 3H]

To clarify, I thought of the number of protons past the most recent noble gas, as any "earlier" proton would be canceled by the inner shell electrons.