Which has the greater bond lengths: NO2^- or NO3^- ? Explain.

Name: Problem 6, Chapter 8: Chemistry
Uploaded: 2019-08-17T22:45:38-08:00
Duration: 6 min 33 s
Channel: Lena Jake
Description: Which has the greater bond lengths: NO2^- or NO3^- ? Explain.

Which has the greater bond lengths: NO2^- or NO3^- ?...

Key Concepts

Bond Order

Bond order is the average number of chemical bonds between a pair of atoms. It is directly related to bond strength and inversely related to bond length; a higher bond order means shorter, stronger bonds, while a lower bond order indicates longer, weaker bonds.

Resonance Structures

Resonance involves drawing multiple valid Lewis structures for a molecule that differ only in the placement of electrons. This concept is crucial for understanding molecules like NO2? and NO3?, where the delocalization of electrons over different bonds provides an averaged bond order that governs bond lengths.

Electron Delocalization

Electron delocalization refers to the spread of electron density over multiple atoms, rather than being confined to a single bond pair. In polyatomic ions, delocalization results in uniform bond lengths that are intermediate between single and double bonds, affecting molecular stability and bond properties.

Relationship Between Bond Order and Bond Length

There is an inverse relationship between bond order and bond length. As bond order decreases, the bond length increases because fewer shared electrons in the bond lead to reduced attractive force between the bonded atoms, thereby resulting in longer bonds.

Transcript

00:01 So in this video we're going to work through question 6 from chapter 8 which asks us which has the greater bond length and no 2 minus or in 03 minus explain.

00:09 So let's go ahead and draw the lewish structures for in 02 minus and then do a little comparison of them.

00:17 So we know that nitrogen is going to bring five valence electrons and each of our two oxygen atoms will bring six valence electrons and then we have a minus one charge so we're going to have one extra electrons so we have a total of 18 valence electrons to work with when we're drawing our lewish structure.

00:35 Let's go ahead and put our nitrogen atom as our central atom and then we have our two oxygen atoms.

00:42 So one possibility that we could do would be to singly bond each oxygen atom to my central nitrogen atom and then fill in the octets.

00:56 So when i do that, i actually have two electrons left over.

01:02 Remember i have 18 valence electrons total and i've only used 16, so i'm going to put those two extra electrons on my central nitrogen atom.

01:09 So is this a good lewis structure? how do we know? well, we can look at the formal charges on each atom.

01:15 So the formal charge is equal to the number of valence electrons minus the number of electrons in lone pairs around the atom, minus half of the number of electrons in bonds that that atom is making.

01:26 So in oxygen, we have six minus six minus one.

01:31 That gives us a formal charge of minus one on both of our oxygen atoms.

01:35 And then what about our central nitrogen atom? we have five valence electrons minus two, minus two in bonds.

01:42 So that gives us a formal charge of plus one.

01:44 So we have formal charges of minus one, plus one, and minus one.

01:48 But we can do a little better than that.

01:50 So what if instead of both of our oxygen atoms being singly bonded, one of them was actually doubly bonded? and then we still have our two electrons on our central nitrogen atom.

02:02 What happens to the formal charges now? well, now the oxygen atom on the right has a formal charge of zero because we have 6 minus 4 minus 2.

02:13 So that has a formal charge of 0.

02:15 And the central nitrogen atom now has a formal charge of 5 minus 2 minus 3.

02:21 So that's a formal charge of 0.

02:23 And then we just have the formal charge of minus 1 on the oxygen atom on the left.

02:27 So by getting our formal charges on more atoms to be 0 ,000.

02:31 We came up with a better lewis structure.

02:35 But this is actually, this lewis structure is what we call resonant stabilized.

02:39 So there's a different way of writing this and an equivalent structure.

02:44 We could have the doubly bonded oxygen atom as the atom on the left rather than the atom on the right.

02:54 And these two structures are equivalent.

02:58 So which one is actually going to be the structure? which one's going to have a double bond and which one's going to have a double bond and which one's going to going to have a single bond.

03:06 Well, what actually happens, because these two structures are equivalent, the structure, the true structure will be an average of them.

03:15 So the true bond lengths for both of these no bonds will be somewhere between a single bond and somewhere between a double bond because of this resonant stabilization.

03:24 So what about no3 minus? well, we know our nitrogen brings five valence electrons, then we have three oxygen atoms, each bringing six valence electrons.

03:32 Our overall charge is minus one, so we have one extra...

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