Sapling Weeks 5-6 HW Question 2

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Vivian Leung 1C
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Sapling Weeks 5-6 HW Question 2

Postby Vivian Leung 1C » Sat Nov 07, 2020 6:22 pm

Hello everyone,

I am having trouble knowing where to place the formal charge on the lewis structure. Can someone explain to me using question number 2 on the Sapling Week 5-6 HW? The question and my answer are shown in the attachment. I am not sure what I am doing wrong because I calculated the formal charge for each atom based on the formula from Dr. Lavelle's lecture but my answer is wrong according to sapling.
Attachments
Sapling Weeks 5-6 HW Question 2.PNG

Namratha Gujje
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Re: Sapling Weeks 5-6 HW Question 2

Postby Namratha Gujje » Sat Nov 07, 2020 6:36 pm

I think that the issue here is that you calculated the incorrect formal charges. The equation for finding the formal charge is
FC = Valence Electrons - (# of bonds/2 + Lone Pairs). If you were to do that for NH4+, then you should get a different numbers. For H it would be FC = 1 - (2/2 + 0). The FC would be zero for all the Hydrogens. For Nitrogen it would FC = 5 - (8/2 + 0). The FC = 1. This also can be checked by looking at the overall compounds charge which is +1. For C032-. If you follow the same equation above you should get different values for the FC of CO32-.

Vivian Leung 1C
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Re: Sapling Weeks 5-6 HW Question 2

Postby Vivian Leung 1C » Sat Nov 07, 2020 6:43 pm

Thank you, that makes sense. I just realized that I calculated for all of the like-atoms together rather than just the single atom.

arisawaters2D
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Re: Sapling Weeks 5-6 HW Question 2

Postby arisawaters2D » Sat Nov 07, 2020 8:54 pm

How do you know when it's best to use a double bond as opposed to using a single bond and a lone pair?

John Pham 3L
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Re: Sapling Weeks 5-6 HW Question 2

Postby John Pham 3L » Sat Nov 07, 2020 9:39 pm

arisawaters3D wrote:How do you know when it's best to use a double bond as opposed to using a single bond and a lone pair?


it depends on the molecule but for the most part, you'd use a double bond over a single bond and a lone pair if it reduced the formal charges on the atoms.
The structure with the lowest formal charges would be the most stable structure.

Haochen He 3L
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Re: Sapling Weeks 5-6 HW Question 2

Postby Haochen He 3L » Sun Nov 08, 2020 5:17 am

arisawaters3D wrote:How do you know when it's best to use a double bond as opposed to using a single bond and a lone pair?

I think it depends on the formal charge. It is better for atom to have 0 formal charge because it's more stable. So if a double bond can make the atom's formal charge equal to 0, then draw the doulbe bond instead of single bond.

Jaclyn Schwartz 1I
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Re: Sapling Weeks 5-6 HW Question 2

Postby Jaclyn Schwartz 1I » Sun Nov 08, 2020 6:48 pm

arisawaters3D wrote:How do you know when it's best to use a double bond as opposed to using a single bond and a lone pair?


If you want to lower the number of bonds. Because in a double bond creates a double bond, while a single bond will leave two lone pairs, one lone pair on each of the atoms in the bond.

Yeprem
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Re: Sapling Weeks 5-6 HW Question 2

Postby Yeprem » Sun Nov 08, 2020 9:42 pm

just make sure to use the formula FC(element x)= (# valence electrons of x) - (# bonds of x/2 + # lone pairs of x)


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