Calculate formal charges for the nonhydrogen atoms in the following molecules: (a) Diazomethane,

Calculate formal charges for the nonhydrogen atoms in the...

Key Concepts

Multiple Bonds

Multiple bonds, such as double or triple bonds, represent the sharing of more than one pair of electrons between two atoms. Understanding the nature of multiple bonds is crucial in formal charge calculations because these bonds contribute more electrons to the bonding count, affecting the division of electrons between atoms and hence the formal charges assigned.

Valence Electron Counting

Valence electron counting involves determining the number of electrons in the outermost shell of an atom, which participate in bonding. This process is fundamental when constructing Lewis structures and calculating formal charges because it sets the baseline for each atom’s typical electron count in its isolated state.

Formal Charge

Formal charge is a concept that assigns a charge to an atom in a molecule based on a comparison between the number of valence electrons in the free atom and the electrons that 'belong' to the atom in the molecule. It is calculated using the formula: formal charge = (number of valence electrons) – (number of nonbonding electrons) – (½ × number of bonding electrons). This is key to understanding how electrons are distributed within a molecule.

Lewis Structures

Lewis structures are diagrams that show how atoms in a molecule are bonded and where lone pairs of electrons are located. They provide the framework for determining how electrons are shared among atoms and are essential for the calculation of formal charges, as they visually represent the bonding arrangement and lone pair distribution.

Transcript

00:01 They want us to calculate the formal charges for the non -hydrogen atoms in each of the polymolecules.

00:05 Now, i'm going to do it slightly differently from how they do it in the book.

00:09 They tell us to use this formula, but i think that formula is kind of cumbersome.

00:15 So what we're going to do instead is do this.

00:22 So we're going to do...

00:24 So formal charge, so fc is going to be the amount of electron.

00:31 We normally have, so normal electrons, then we minus how many we actually have for our electrons.

00:43 And it'll be a little bit, make more sense what i mean by normal and have in a second.

00:48 So let's go ahead and start with a.

00:50 So for this carbon here, let's go ahead and actually draw these two hydrogens out.

01:00 So what i like to do is draw a octet in some sense going around it.

01:06 And so now, since these are covalent bonds, that means each of the bonds is going to be sharing one carbon or one electron with each of those.

01:16 So we have one bond here, one bond here, one pond here, one pond here, and one pond here.

01:22 So this means this carbon here has four electrons, essentially for itself.

01:29 So we can come over here to our chart now.

01:32 And remember, this has one electron, two, three, four, four, five, six, seven, eight, and its neutral state as an atom.

01:42 So we would just compare.

01:43 What we have four? and this carbon over here, well, it should have four as well.

01:50 So the formal charge on this is going to be zero.

01:53 So formal charge is zero for this carbon.

01:59 Now what about this nitrogen here? well, let's do the same thing.

02:03 So we can make another little octet that surrounds it like this.

02:07 So each of the bonds is going to be one electron that it has.

02:14 And so that's going to be four.

02:17 So we come over here and we see that nitrogen normally has five.

02:21 So we would do five.

02:24 So it would be five minus four, which gives us one.

02:28 So the formal charge for that nitrogen there is going to be one.

02:33 And then last will we come over to here.

02:36 And so in our octet.

02:41 Notice that, or maybe i should be calling this octet in our orbitals, i should say, in some sense.

02:50 This is going to have, so the two bonds give us one electron each, and then we just count up the lone pairs.

02:57 So we'd have one, two, three, four, five, six.

03:00 So it has six, but nitrogen, or actually i put this in the opposite order.

03:07 So nitrogen normally has five, but it has six, so that's going to give us negative one.

03:16 So the formal charge for that nitrogen is negative one.

03:19 So i think just doing like this normally is a little bit quicker, as opposed to memorizing some formula.

03:27 So let's go ahead and do this the same for this other one down here.

03:31 So let's draw these hydrogens out.

03:35 So one, two, three...

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