Formal Charge: Lewis dot structures


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Jocelyn Fermin1J
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Joined: Tue Nov 14, 2017 3:01 am

Formal Charge: Lewis dot structures

Postby Jocelyn Fermin1J » Fri May 11, 2018 9:25 am

Can someone explain how to find the formal charge for elements in Lewis dot structures? If you can include an example that would be very helpful
Thank you in advance!

Andrea- 3J
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Joined: Tue Nov 14, 2017 3:00 am

Re: Formal Charge: Lewis dot structures

Postby Andrea- 3J » Fri May 11, 2018 9:38 am

There's an equation to find formal charge.
FC=V-(N+(B/2))

FC=formal charge
V=number of Valence electrons
N=number of non-bonding valence electrons
B=total number of electrons in covalent bonds with other atoms in the molecule

Example: the formal charge of Oxygen (O) in Carbon Dioxide (CO2)
V=6
N=4
B=(4/2)=2

FC=6-(4+2)
FC=6-6
FC=0
Oxygen has a formal charge of 0.

Elizabeth Parker 1K
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Re: Formal Charge: Lewis dot structures

Postby Elizabeth Parker 1K » Fri May 11, 2018 11:34 am

Do we always need to find formal charge?

Adela Henry 1I
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Re: Formal Charge: Lewis dot structures

Postby Adela Henry 1I » Fri May 11, 2018 1:40 pm

Most likely yes because finding the formal charge helps to draw the most stable Lewis structure of the molecule.

Jacob Samuels 1E
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Re: Formal Charge: Lewis dot structures

Postby Jacob Samuels 1E » Fri May 11, 2018 1:44 pm

Ideally, all your formal charges would be between -1 and 1, and you should change the structure to allow for the maximum amount of FC=0 as possible.

EllenRenskoff-1C
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Re: Formal Charge: Lewis dot structures

Postby EllenRenskoff-1C » Fri May 11, 2018 4:10 pm

I am confused about when we can add double bonds versus when we just add electrons to certain elements in the given compound to make the formal charge closer to zero. How would we know what the best way to do that is in order to draw the proper Lewis dot structure?

Alejandro Salazar 1D
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Re: Formal Charge: Lewis dot structures

Postby Alejandro Salazar 1D » Fri May 11, 2018 6:24 pm

EllenRenskoff-1C wrote:I am confused about when we can add double bonds versus when we just add electrons to certain elements in the given compound to make the formal charge closer to zero. How would we know what the best way to do that is in order to draw the proper Lewis dot structure?


On the attached file, you can see I added a double bond between both carbon because on the structure on left, only used 10 electrons. Therefore, I still needed to add two electrons. Hydrogen are an exception from the octet rule but not carbon. Carbon needs a full octet, 8 electrons. With this double bond, both carbon share 2 electrons, making both an octet rule.

You add double or triple bonds to reach octet by sharing electrons.
Attachments
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