Classification of Ligands - Video Tutorials & Practice Problems
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concept
Ligand Classification
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In this video, we're gonna take a more in depth look at different types of ligands or ligands. Now recall they represent Lewis bases because they have at least one long pair that can be donated. And when it comes to their classification, they're classified by the number of donor atoms that can donate one lump pair to the central metal. When we talk about ligands or liking classifications, we have mono dentate bate and poly dentate in a Monod dentate ligand, we can donate only one lone pair from one donor atom in a bent A it's two donor atoms and polly, it's going to be more than two. Now, before we take a look at the list, let's just understand how do we find the number of donor atoms? Now, we're gonna say two or more atoms with lone pairs. OK. To find the number of donor atoms, two or more atoms with lone pairs. Rule one is donor atoms must be separated by two or more atoms and rule two atoms with a negative charge equal the donor atom, right. So let's come up here and see for the mono dentate ligands or ligands. It's pretty easy to see them because there's only one structure that can donate a long pair for hydroxide O has a negative chart. So what represents our donor atom X represents a halogen it's negatively charged. So here, it's the donor atom in ammonia. Only nitrogen has a lone pair. So it's a donor atom in water. It donates one of these lone pairs for cyanide, the negative charges on the carbon in terms of formal charge. So it is the donor atom. Now we're gonna say carbon monoxide here, remember carbon ideally wants to make four bonds and carbon monoxide, it's only making three bonds. So it would love to share this lone pair in order to make that fourth bond. So it is the donor atom. Next we have here cata coate in it, the oxygens are just making one bond. So their formal charges are minus one. We would say here, remember, donor atoms must be separated by two or more atoms. These two negatively charged oxygens are separated from each other by 12 atoms. So both of them can act as donor atoms. We have two donor atoms here. Obsolete here, this oxygen and this oxygen are negative in terms of formal charge. So there are the two donor atoms and they're separated by two atoms from each other. Next, we have ethyl ethylene diamine. Its abbreviation is en here, it's the nitrogens that have long pairs. They're the ones that can act as the donor atoms they're also separated from each other by two carbons, two atoms. Now poly dentate, we usually don't see very much of this in gen chem. For those of you who take higher advanced more chemistry such as organic chemistry or a local chemistry or even in organic chemistry, you'll come into more of a full view of these types of ligands for here. Just remember they're the ones that have more than two donor atoms. A good example here is uh di ethyl diy triamine. So we'd have one, 23 donor atoms and then finally, we have EDT A which is ethylene diamine tetra acetate. Now, here, this one actually has six donor atoms within it. You're not responsible in knowing its structure. Just realize that it's the most famous of all the poly dentate ligands or Lincolns that exists. If you look on different types of food packaging, you'll see EDT A as part of the ingredients. Um It works as a uh preservation agent for a lot of types of foods. Um It's pretty common in a lot of things. OK. So just remember EDT A is just a common type of poly dentate. You don't need to know the structure. It's poly dentate because it has more than two donor atoms in this case. Six. All right. So keep this in mind when we're looking at different types of ligands
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example
Classification of Ligands Example
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Here, it says classify the following anionic ligands as mono dentate, bent and poly dentate. For the first one here, this is called our army ion. It's nitrogen here. It's only making two bonds, but it's negatively charged. That happens when nitrogen has two lone pairs. It is the only structure with lone pairs. So there's only one donor atom here. So this would be mono dentate for the next one here. This structure, we have an oxygen that's double bonded. So it would have two would have two lone pairs on it. Remember when oxygen is single bonded, it has three lone pairs, one of which could be a donor element. And remember oxygen, when it's single bonded, it has a minus one formal charge. That's what give gives us the overall minus one charge here. So this oxygen at single bonded is one of the donor atoms, but it's not the only one nitrogen here is making three bonds. It's making one to the carbon and two more to the two hydrogen. So that's three bonds. So it has a long pair that we don't see, it also serves as a donor atom. So that's two donor atoms Now, what about this oxygen down here? That's double bonded, well, for us to have it act as a donor atom, it needs to be two more atoms away from the single bonded oxygen. It's not, it's only one carbon away. So it can't be counted as a donor. So in this structure, we'd say that we have two donor atoms. So this would be a bi dentate ligand, right? So this would be our answer for each of them. So we'd have mono dentate and bent as our answers.
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concept
Chelating Agents
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Here, we're gonna talk about chelating agents. Now, bent and poly dentate ligands or lions are considered chelating agents. Now a chelating agent, um they create ring structures in the complex ion when donor atoms bond to the central atom of metal, which we're gonna call m So here, what do we have? We have? This is Monod, this is Monod and this here is our bent liar Ln attached those two nitrogens, each had a lone pair which they used to connect to the metal. And as we can see, we've created a ring on the left side, this here would represent its overall complex ion structure formula. Now, here we're gonna say complex form with key lighting agents are more stable then with mono dentate li ans. And when we talk about stability of these rings, ideally, we're trying to make five or six membered rings. If we're to count this out with C 12345, five and six membered rings are pretty common when it comes to these bent and potty dentate ligands or ligands, right? So just keep that in mind, we're looking at different types of attachments that occur when they connect to our central metal.
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example
Classification of Ligands Example
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Chelating agents can be used to remove toxic heavy metals from the human body by forming stable complex ions with the metal identify a ligand or ligand that is capable of removing excess lead. So remember we learned earlier that bate and poly dentate ligands or ligands are the best type of uh ligands to use as chelating agents. If we take a look here, C is out because C is mono dentate because only sulfur here can donate its lone pairs at that time. If we take a look at the others, we're gonna say here that this oxygen is negative and this oxygen here is negative, but we can't count both of them as helping to be bated because they have to be separated by two or more atoms from one another. They're only separated by one carbon. So only one of them would actually act as a donor atom at a time. So this is out a is the answer because in a, we have this oxygen single bonded. So its charge is negative one, same with this sulfur and same with this oxygen and same with this sulfur, each of these negatively charged or negative one formal charged atoms is at least two atoms away from the next one. So they each connect as a donor atom. In this case, we have four donor atoms within this structure. So it'd be poly dentate so it could form or act as a chelating agent. So out of all the options, only option A is the correct choice.
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Problem
Problem
How many donor atoms are in each ligand?
A
a) 2 b) 2 c) 3
B
a) 1 b) 1 c) 2
C
a) 2 b) 1 c) 3
D
a) 1 b) 2 c) 4
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