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As mentioned above, the overall charges should add up to the charge of the molecule. However, you usually want more of the atoms to have a formal charge of zero, so if you can make a structure in which the overall formal charges add up to the charge of the molecule and have the atoms where it's possible have a formal charge of zero, that is more stable (for example, if the overall charge of a molecule is -1, then it is more stable to have atoms that have a formal charge of 0 and -1 than atoms with formal charges of +1 and -2).
I learned that you should try to minimize the absolute charge on the atoms in the molecule/ion. Therefore, if an ion has an overall +1 charge, it should be achieved by 0 charges and a single +1 charge, instead of say a -3 and a +4 charge.
Another important rule to note is that if an atom does have to a formal charge, it is more stable for a negative formal charge to be placed on the atom with the higher electronegativity, since that is the atom that pulls on electrons more and thus achieves that negative charge.
Hope that helps!
Hope that helps!
The main goal is to minimize charges. So however you can get the charges to be lowest, while still adding up to the total charge and following octet rules etc. Placing larger charges on more electronegative elements is also important.
Try to draw the lewis structure where it will be the most stable unless the questions asks you otherwise or to match the charge on the molecule given in the question. Ultimately, make sure you are addressing the question.
aphung1G wrote:When drawing regular lewis structures do you always have to draw them where their formal charges are zero?
The lower the formal charge, the more stable the structure. In theory, yes the formal charges for each atom doesn't have to be zero, but the closer to zero the better, because of this stability.
When you draw lewis structures, they don't always have to have 0 formal charges and indeed it just depends on the molecule. The molecule itself could be positively charged or negatively charged and this means that for sure one of the atoms will have to be with a charge. When drawing the "best" Lewis structure however you want to make is that it is in the lowest possible state so you want as many 0 charges for the atoms unless they need it and sometimes you have to decide where the negative or positive charge will go more appropriately. Like if there needs to be a negative charge and there is two atoms, a C and O then you obviously want the O to hold the negative charge because it is more favorable this way.
When you draw Lewis structures, you just try to get the lowest energy structure possible, typically with a 0 formal charge where possible. If not, I think you just make the entire charge of the atom match what is given.
Lewis structures should have formal charges closest to zero as much as possible. The formal charges of each atom should sum up to equal the overall charge, which varies for some molecules; If a molecule has an overall charge of zero, then the formal charges of each atom should most preferably be zero, or at least close to zero.
You don't always need to write in the atom's formal charges next to elements but you should always draw them in consideration of formal charges because formal charges closest to 0 means the molecule is most stable, which is what we are aiming for. But don't just draw them so everything has a formal charge of 0 because some molecules have specific net charges which your formal charges should sum up to.
As others have said, formal charges must add up to the overall charge of the molecule you are drawing. However, when it comes to determining which atom(s) gets the non-zero formal charge(s), use electronegativity. For example, if you draw the lewis structure for the chlorate ion (ClO3-), when deciding whether the Cl or the O should get the -1 formal charge, notice that oxygen is more electronegative than chlorine, and therefore would prefer to have the -1 over the chlorine.
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