Assign formal charges to the atoms in each of the following molecules: (a) (b) H3 C-N̈-N ≡N: (c)

step 1 They want us to assign formal charges to all of the atoms here. So let's go ahead and start that

Assign formal charges to the atoms in each of the following...

Key Concepts

Formal Charge

Formal charge is the hypothetical charge assigned to an atom in a molecule, calculated by subtracting the number of electrons assigned to the atom (using a method of equal splitting in bonds) from the number of valence electrons the atom normally possesses. This concept helps in evaluating the charge distribution within a molecule and in determining its most likely structure.

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms of a molecule and the lone pairs of electrons that may exist. They provide a visual method to account for the total number of valence electrons in a molecule, establish connectivity, and set the stage for formal charge calculations.

Octet Rule

The octet rule is a guiding principle in chemical bonding which states that atoms tend to form bonds until they are surrounded by eight electrons, achieving an electron configuration similar to that of noble gases. This rule helps predict the arrangement of electrons in a Lewis structure and informs adjustments such as formal charge distribution when ideal octet configurations are not met.

Electron Counting and Bonding Arrangements

Electron counting involves tallying both the bonding electrons (shared equally between atoms in a bond) and the nonbonding or lone pair electrons around atoms. Correct electron counting is crucial for drawing accurate Lewis structures and for assigning formal charges, particularly in molecules with multiple bonds or varied distribution of electron pairs.

Transcript

00:01 They want us to assign formal charges to all of the atoms here.

00:05 So let's go ahead and start that.

00:08 So let's first draw out these other hydrogens that we have first.

00:20 So i'm going to do this slightly differently from how they do it in the book.

00:26 You can use that formula that they give, but i feel like that takes too much time to kind of do.

00:34 Well, maybe not too much time, but just remembering the formula, i think, is a little bit too much of a hassle.

00:44 Now, one thing that we can say, without really thinking about it too much, is all these hydrogens are going to have a formal charge of zero, so they're all going to be neutrally charged.

00:54 And we know that just because they normally only have one electron in their valence, and if they're forering one bond, then they have one.

01:03 So all the hydrogens that we have here are going to be neutrally charged, so let's just ignore those.

01:07 But now what about the non -hydrogen atom? so in the case of this carbon up top here, what i like to do is draw a valent shell going around it.

01:16 And it's not quite a valence shell, but at least the idea kind of holds.

01:22 And for each of these bonds, since this is a covalent bond, those are where the electrons are shared.

01:27 So there's two electrons in each of the bonds.

01:31 So that means if it's going to be shared, that means the carbon has at least one of them.

01:35 So this carbon has four electrons.

01:38 And it normally has four electrons, so that would be zero.

01:42 Actually, maybe i should write off on the side here, how many electrons these normally have.

01:46 So hydrogen normally has one, carbon normally has four, oxygen normally has six, and nitrogen normally has five.

01:58 So we'll just kind of keep that off on the side there.

02:01 Now let's move on to our nitrogen here.

02:06 So each of these four bonds will donate one electron.

02:10 To this nitrogen.

02:12 So this has four electrons, but it normally has five.

02:16 So it has one less of what it normally has.

02:19 So that means it's going to be positively charged or as a formal charge of positive one.

02:26 Now what about this oxygen off on the right here? so we'll do the same thing.

02:33 This bond here has one electron that's donated to the oxygen, adding all this up.

02:39 That has seven in total.

02:41 We said that oxygen normally has six.

02:44 So that means it has one more than what it normally has.

02:46 So that's going to be a negative charge.

02:49 So i have a formal charge of negative one.

02:52 What about our carbon over here? so we can do the same thing is that top carbon.

02:59 And you'll notice that it'll look exactly like what we have up there.

03:02 So this is actually going to be neutrally charged.

03:04 So a formal charge of zero...

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