Draw as many resonance structures as possible for each of...

Key Concepts

Formal Charge and Electron Delocalization

Formal charge is a bookkeeping tool used to determine the distribution of electrons in a molecule; it helps in choosing the most stable resonance structures by minimizing charges on atoms where possible. Electron delocalization refers to the spreading out of electrons over several atoms, which can lower the overall energy of the molecule and is explicitly illustrated by the resonance forms.

Lewis Structures

Lewis structures are diagrams that show the bonding between atoms of a molecule as well as the lone pairs of electrons that may exist. They serve as the starting point for understanding electron distributions in a molecule, facilitating the identification of possible resonance forms while considering both bonding and non-bonding electrons.

Octet Rule

The octet rule states that atoms (except hydrogen) tend to form bonds in such a way that they have eight electrons in their valence shell. In drawing resonance structures, special care is taken to ensure that all atoms (where applicable) achieve an octet, which is often a key criterion for the stability of the resulting structures.

Resonance Structures

Resonance structures are different valid Lewis representations of the same molecule or ion that differ only in the distribution of electrons, not the positions of the atoms. These structures illustrate the delocalization of electrons and help to explain the stability and properties of the molecule, as the true electronic structure is a hybrid of all the resonance forms.

Transcript

00:01 This question is in reference to resonant structures, and you're asked to draw as many resonant structures as possible for each of the following molecules or ions.

00:11 The first one is so2.

00:15 To draw the resonant structures, we must first draw the electron dot structure.

00:20 And before we can draw the electron dot structure, we need to know the number of valence electrons.

00:24 Sulfur has six, there's one of them.

00:27 Oxygen has six.

00:28 There are two of them.

00:29 So we have a total of 18 valence electrons.

00:31 So if we put sulfur in the middle and we put the three oxygens around it, we will end up, i'm sorry, the two oxygens around it, we will end up with four valence electrons having been used.

00:44 That means we have 12 left over.

00:46 So we've got one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve.

00:54 We've got, sorry, fourteen, four, off of the 18 is 14.

01:00 We just used up 12, so we got two more.

01:02 So we'll put those two there on sulfur.

01:04 The oxygens have an octet.

01:05 The sulfur does not.

01:07 So what we need to do is we need to take a lone pair off of one of the oxygens and have it become a bonding pair.

01:15 If we can take it off the oxygen on the right, we could have taken it off the oxygen on the left, and we would get this as our second resonant structure.

01:29 The second species is carbonate, co3 -2 -1.

01:35 Carbon has four valence electrons, there's one of them.

01:38 Oxygen has six, there are three of them, plus we have two more valence electrons from the two minus charge.

01:45 That gives us a total of 24 valence electrons.

01:49 So if we put carbon in the middle and put all three oxygens around it, that will give us, well, we would have consumed six valence electrons, so we have 18 left over.

02:00 So we could go 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.

02:05 13, 14, 15, 16, 17, 18.

02:08 We used up all the valence electrons.

02:10 All the oxygens have an octet, but the carbon does not.

02:14 So we need to take a lone pair of electrons from one of the oxygens and make it a bonding pair...

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