Negative Sign

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Anna Martin 2l
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Negative Sign

Postby Anna Martin 2l » Sat Nov 07, 2020 1:15 pm

Hi, I was just wondering if anyone could clarify how to figure out where the negative sign goes when constructing a lewis structure, whether it's outside the molecule or on a specific element. Thanks!

Mackenzie Fernandez 3G
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Re: Negative Sign

Postby Mackenzie Fernandez 3G » Sat Nov 07, 2020 1:34 pm

hi!

I think what you are referring to is when Dr. Lavelle does the formal charge of an atom (minus sign on a specific element) compared to the charge of a molecule overall when drawing a lewis structure (minus sign outside of molecule)? So I think when we are asked questions about this, they will specify whether they want to know the lewis structure or both the lewis structure and FC.

Hope this helps!

Lea Baskin Monk 1F
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Re: Negative Sign

Postby Lea Baskin Monk 1F » Sat Nov 07, 2020 1:35 pm

You draw the negative sign outside the molecule (with the brackets) when you have drawn the lewis structure of an ion. For example, if you draw the lewis structure for PO4^3- your entire drawing with have brackets around it and a 3- indicating that the structure represents an ion with a 3- charge.

The negative sign is drawn on an individual atom in the molecule when you are referring to the formal charge of that atom being negative. The formal charge is found using the formula
Fc = valence - (lone pairs + (shared/2).

Sophia Spungin 2E
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Re: Negative Sign

Postby Sophia Spungin 2E » Sat Nov 07, 2020 2:42 pm

The number on the outside is the overall charge of the molecule. This has to do with the total number of electrons present versus the expected number present from the elements. The numbers next to the individual atoms is the formal charge, and the sum of all of these formal charges is equal to the net charge.

Emma Strassner 1J
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Re: Negative Sign

Postby Emma Strassner 1J » Sat Nov 07, 2020 3:45 pm

If you're talking about the negative on the molecular formula itself, you use the brackets to put it outside the drawing of the Lewis structure. Otherwise, you are talking about the negative that goes with the charge of each atom in the molecule individually, so it goes with the atoms themselves.

ellenulitsky Dis 1I
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Re: Negative Sign

Postby ellenulitsky Dis 1I » Sat Nov 07, 2020 5:51 pm

When finding the charge of the lewis dot structure, I first find the charge of each individual atom and then add up the charges to find the total charge! Hope this helps.

Sedge Greenlee
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Re: Negative Sign

Postby Sedge Greenlee » Sat Nov 07, 2020 7:27 pm

The total charge is written outside of the brackets when you are giving the charge of an ion molecule. Dr. Lavelle also reccomended underlining each atom's formal charge number to distinguish these charges from the total charge.

Tanya Nguyen 1B
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Re: Negative Sign

Postby Tanya Nguyen 1B » Sat Nov 07, 2020 11:21 pm

The charge of the overall molecule goes outside of the Lewis structure which is in a square bracket. You could also write the charge of each individual atom, Dr. Lavelle recommends underlining the formal charge of the individual atom to make it easier to distinguish.

Brendan Duong 1I
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Re: Negative Sign

Postby Brendan Duong 1I » Sat Nov 07, 2020 11:22 pm

Anna Martin 2l wrote:Hi, I was just wondering if anyone could clarify how to figure out where the negative sign goes when constructing a lewis structure, whether it's outside the molecule or on a specific element. Thanks!


The one that goes outside the brackets is the overall charge. Next to each element on the lewis structure, you should put its formal charge. This is determined by the equaiton FC=Valence electrons-Lone elections-number of bonds. This is also what the sapling questions want you to find out . All the FC together should equal the overall charge

Eric Cruz 2G
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Re: Negative Sign

Postby Eric Cruz 2G » Sun Nov 08, 2020 12:00 am

There will be a negative sign (or positive sign) if there is a total charge on the entire molecule. For example NO3-'s lewis structure is bracketed because the total charge of the molecule isn't zero. When you do the formal charges of each atom, N has a formal charge of +1, the two oxygens with a single bond have a formal charge of -1 and the oxygen with a double bond has a formal charge of 0. Therefore in total, there is -1 charge and is why we bracket the problem. In addition, the molecule itself notes there is a -1 charge in its structure (NO3- the minus means there's a total -1 charge).

Joel Meza 3I
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Re: Negative Sign

Postby Joel Meza 3I » Sun Nov 08, 2020 2:06 pm

If you are talking about the charge of the molecule represented by the Lewis structure, then the charge (along with its number) will go outside of the structure's brackets.

Sophia Kalanski 1A
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Re: Negative Sign

Postby Sophia Kalanski 1A » Sun Nov 08, 2020 3:46 pm

The negative sign will be on the outside of the molecule and it is used to dictate the charge of the molecule based on how many electrons it will need to complete an octet and to be stable

Neha Gupta 2A
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Re: Negative Sign

Postby Neha Gupta 2A » Sun Nov 08, 2020 3:50 pm

In molecules such as OH-, the negative sign represents the overall charge of the molecule andwill be outside of the brackets. However for formal charge, each atom in the molecule has its own charge which is different from the charge outside the brackets. The sum of the formal charges should equal the charge on the outside of the brackets.


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