Formal charge formula = [# of valence electrons] – [electrons in lone pairs + 1/2 the number of bonding electrons]
Examples:
Find the formal charge for the nitrogens in the problem.
1. Look at the number of valence electrons for nitrogen. Nitrogen has 5.
Use the SHORTCUT formula= [# of valence electrons on atom] – [non-bonded electrons + number of bonds]
Example 1.
[5]-[4] = +1 charge
[5 is for the valence electrons of nitrogen] - [3 is for hydrogen bonds and 1 carbon bond = 4 (there aren't any non-bonding electrons)]
Which is why you get +1.
Example 2:
[5]-[3 bonding + 2 non-bonding] = 0
Example 3:
[5] - [4 bonding] = +1
Example 4:
[5] - [2 bonding+4 non bonding] = -1
Hope this refreshed your memory from the beginning of the semester!
Links:
http://www.masterorganicchemistry.com/2010/09/24/how-to-calculate-formal-charge/
This is a really detailed explanation on how to determine formal charges. The shortcut is also quite easy to remember. Great job!
ReplyDeleteThis is great. Something that I definitely still struggle with from time to time. Thanks!
ReplyDeleteI really liked all the examples on this one! Nice post!
ReplyDeleteYesss this is a good one. Something that I need to brush up on since it has been so long ago. You were very detailed but straight to the point.
ReplyDeleteThank you for such a detailed explanation of this problem. I always get confused on the formula for how to calculate formal charge. You make it so much easier to remember how to do!
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